U.S. patent application number 17/143848 was filed with the patent office on 2021-07-22 for pinna proximity detection.
This patent application is currently assigned to Cirrus Logic International Semiconductor Ltd.. The applicant listed for this patent is Cirrus Logic International Semiconductor Ltd.. Invention is credited to Jeffrey D. ALDERSON, Thomas I. HARVEY, Jon D. HENDRIX, Robert LUKE, Viral PARIKH, Nafiseh Erfanian SAEEDI, Vitaliy SAPOZHNYKOV.
Application Number | 20210225352 17/143848 |
Document ID | / |
Family ID | 1000005507288 |
Filed Date | 2021-07-22 |
United States Patent
Application |
20210225352 |
Kind Code |
A1 |
PARIKH; Viral ; et
al. |
July 22, 2021 |
PINNA PROXIMITY DETECTION
Abstract
An integrated circuit for implementing at least a portion of a
personal audio device may include an output for providing an output
signal to a transducer, wherein the output signal includes a pilot
signal, a microphone input for receiving a microphone signal from a
microphone indicative of an output of the transducer, and a
processing circuit. The processing circuit may be configured to
implement a pilot signal control to apply an adjustment to the
pilot signal as necessary to maintain the pilot signal at a
substantially constant magnitude regardless of proximity of the
transducer to a pinna and implement a proximity determination block
configured to determine proximity of the transducer to the pinna
based on the adjustment.
Inventors: |
PARIKH; Viral; (Austin,
TX) ; HENDRIX; Jon D.; (Wimberley, TX) ;
ALDERSON; Jeffrey D.; (Austin, TX) ; SAPOZHNYKOV;
Vitaliy; (Cheltenham, AU) ; SAEEDI; Nafiseh
Erfanian; (Bentleigh East, AU) ; HARVEY; Thomas
I.; (Northcote, AU) ; LUKE; Robert; (Richmond
East, AU) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Cirrus Logic International Semiconductor Ltd. |
Edinburgh |
|
GB |
|
|
Assignee: |
Cirrus Logic International
Semiconductor Ltd.
Edinburgh
GB
|
Family ID: |
1000005507288 |
Appl. No.: |
17/143848 |
Filed: |
January 7, 2021 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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16539092 |
Aug 13, 2019 |
10923097 |
|
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17143848 |
|
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62719767 |
Aug 20, 2018 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
G10K 2210/108 20130101;
H04M 1/0202 20130101; G10K 11/17853 20180101; G10K 2210/3056
20130101; G10K 2210/3028 20130101; G10K 2210/3044 20130101; G10K
11/17823 20180101 |
International
Class: |
G10K 11/178 20060101
G10K011/178 |
Claims
1.-42. (canceled)
43. An integrated circuit for proximity detection of a headset
comprising a headset speaker, comprising: a first input for
receiving a first signal from a first headset microphone, the first
signal indicative of headset ambient sound; a second input for
receiving a second signal from a second headset microphone, the
second signal indicative of sound present at an acoustic output of
the headset speaker; and circuitry for comparing a first sound
energy of the first signal and a second sound energy of the second
signal to determine whether the headset is on a user's ear.
44. The integrated circuit of claim 43, wherein the first sound
energy and the second sound energy are within a frequency band.
45. The integrated circuit of claim 44, wherein the frequency band
is 2 KHz to 5 KHz.
46. The integrated circuit of claim 43, further comprising: a
frequency-range isolating filter configured to receive and bandpass
filter the first signal; an envelope detector for detecting a
signal envelope of the first signal in the bandpass filter range;
and a linear-to-decibel converter configured to convert the
envelope detected, bandpass-filtered first signal into a value
given in terms of decibels relative to full-scale magnitude for the
first signal.
47. The integrated circuit of claim 43, further comprising: a
frequency-range isolating filter configured to receive and bandpass
filter the second signal; an envelope detector for detecting a
signal envelope of the second signal in the bandpass filter range;
and a linear-to-decibel converter configured to convert the
envelope detected, bandpass-filtered second signal into a value
given in terms of decibels relative to full-scale magnitude for the
second signal.
48. The integrated circuit of claim 43, further comprising: a first
frequency-range isolating filter configured to receive and bandpass
filter the first signal; a first envelope detector for detecting a
signal envelope of the first signal in the bandpass filter range; a
first linear-to-decibel converter configured to convert the
envelope detected, bandpass-filtered first signal into a value
given in terms of decibels relative to full-scale magnitude for the
first signal; a second frequency-range isolating filter configured
to receive and bandpass filter the second signal; a second envelope
detector for detecting a signal envelope of the second signal in
the bandpass filter range; and a second linear-to-decibel converter
configured to convert the envelope detected, bandpass-filtered
second signal into a value given in terms of decibels relative to
full-scale magnitude for the second signal.
49. The integrated circuit of claim 43, further comprising: a first
frequency-range isolating filter configured to receive and bandpass
filter the first signal; a first envelope detector for detecting a
signal envelope of the first signal in the bandpass filter range; a
first linear-to-decibel converter configured to convert the
envelope detected, bandpass-filtered first signal into a value
given in terms of decibels relative to full-scale magnitude for the
first signal; a second frequency-range isolating filter configured
to receive and bandpass filter the second signal; a second envelope
detector for detecting a signal envelope of the second signal in
the bandpass filter range; a second linear-to-decibel converter
configured to convert the envelope detected, bandpass-filtered
second signal into a value given in terms of decibels relative to
full-scale magnitude for the second signal; circuitry for comparing
a difference between the decibel values of the first and second
signals and comparing the difference to a threshold value and
outputting a control signal; and a proximity decision block
responsive to the control signal and configured to determine
whether the headset is on a user's ear.
50. A headset comprising: a headset speaker; a first headset
microphone; a second headset microphone; and an integrated circuit
for proximity detection of the headset, comprising: a first input
for receiving a first signal from the first headset microphone, the
first signal indicative of headset ambient sound; a second input
for receiving a second signal from the second headset microphone,
the second signal indicative of sound present at an acoustic output
of the headset speaker; circuitry for comparing a first sound
energy of the first signal and a second sound energy of the second
signal to determine whether the headset is on a user's ear.
51. The headset of claim 50, wherein the first sound energy and the
second sound energy are within a frequency band.
52. The headset of claim 51, wherein the frequency band is 2 KHz to
5 KHz.
53. The headset of claim 50, further comprising: a frequency-range
isolating filter configured to receive and bandpass filter the
first signal; an envelope detector for detecting a signal envelope
of the first signal in the bandpass filter range; and a
linear-to-decibel converter configured to convert the envelope
detected, bandpass-filtered first signal into a value given in
terms of decibels relative to full-scale magnitude for the first
signal.
54. The headset of claim 50, further comprising: a frequency-range
isolating filter configured to receive and bandpass filter the
second signal; an envelope detector for detecting a signal envelope
of the second signal in the bandpass filter range; and a
linear-to-decibel converter configured to convert the envelope
detected, bandpass-filtered second signal into a value given in
terms of decibels relative to full-scale magnitude for the second
signal.
55. The headset claim 50, further comprising: a first
frequency-range isolating filter configured to receive and bandpass
filter the first signal; a first envelope detector for detecting a
signal envelope of the first signal in the bandpass filter range; a
first linear-to-decibel converter configured to convert the
envelope detected, bandpass-filtered first signal into a value
given in terms of decibels relative to full-scale magnitude for the
first signal; a second frequency-range isolating filter configured
to receive and bandpass filter the second signal; a second envelope
detector for detecting a signal envelope of the second signal in
the bandpass filter range; and a second linear-to-decibel converter
configured to convert the envelope detected, bandpass-filtered
second signal into a value given in terms of decibels relative to
full-scale magnitude for the second signal.
56. The headset of claim 50, further comprising: a first
frequency-range isolating filter configured to receive and bandpass
filter the first signal; a first envelope detector for detecting a
signal envelope of the first signal in the bandpass filter range; a
first linear-to-decibel converter configured to convert the
envelope detected, bandpass-filtered first signal into a value
given in terms of decibels relative to full-scale magnitude for the
first signal; a second frequency-range isolating filter configured
to receive and bandpass filter the second signal; a second envelope
detector for detecting a signal envelope of the second signal in
the bandpass filter range; a second linear-to-decibel converter
configured to convert the envelope detected, bandpass-filtered
second signal into a value given in terms of decibels relative to
full-scale magnitude for the second signal; circuitry for comparing
a difference between the decibel values of the first and second
signals and comparing the difference to a threshold value and
outputting a control signal; and a proximity decision block
responsive to the control signal and configured to determine
whether the headset is on a user's ear.
57. The headset of claim 50, wherein the headset is a wired headset
for communicatively coupling to an audio device.
58. The headset of claim 50, wherein the headset is a wireless
headset for communicatively coupling to an audio device.
59. The headset of claim 50, wherein the headset is a wireless
earbud for communicatively coupling to an audio device.
60. An integrated circuit for proximity detection of a headset
comprising a first headset speaker and a second headset speaker,
comprising: a first input for receiving a first signal from a first
headset microphone, the first signal indicative of first headset
ambient sound; a second input for receiving a second signal from a
second headset microphone, the second signal indicative of sound
present at an acoustic output of the first headset speaker; a third
input for receiving a third signal from a third headset microphone,
the third signal indicative of second headset ambient sound; a
fourth input for receiving a fourth signal from a fourth headset
microphone, the fourth signal indicative of sound present at an
acoustic output of a second headset speaker; circuitry for
comparing a first sound energy of the first signal to a second
sound energy of the second signal and comparing a third sound
energy of the third signal and a fourth sound energy of the fourth
signal to determine whether the headset is on a user's ear.
61. The integrated circuit of claim 60, wherein the first sound
energy and the second sound energy are within a frequency band.
62. The integrated circuit of claim 61, wherein the frequency band
is 2 KHz to 5 KHz.
63. The integrated circuit of claim 60, further comprising: a
frequency-range isolating filter configured to receive and bandpass
filter the first signal; an envelope detector for detecting a
signal envelope of the first signal in the bandpass filter range;
and a linear-to-decibel converter configured to convert the
envelope detected, bandpass-filtered first signal into a value
given in terms of decibels relative to full-scale magnitude for the
first signal.
64. The integrated circuit of claim 60, further comprising: a
frequency-range isolating filter configured to receive and bandpass
filter the second signal; an envelope detector for detecting a
signal envelope of the second signal in the bandpass filter range;
and a linear-to-decibel converter configured to convert the
envelope detected, bandpass-filtered second signal into a value
given in terms of decibels relative to full-scale magnitude for the
second signal.
65. The integrated circuit of claim 60, further comprising: a first
frequency-range isolating filter configured to receive and bandpass
filter the first signal; a first envelope detector for detecting a
signal envelope of the first signal in the bandpass filter range; a
first linear-to-decibel converter configured to convert the
envelope detected, bandpass-filtered first signal into a value
given in terms of decibels relative to full-scale magnitude for the
first signal; a second frequency-range isolating filter configured
to receive and bandpass filter the second signal; a second envelope
detector for detecting a signal envelope of the second signal in
the bandpass filter range; and a second linear-to-decibel converter
configured to convert the envelope detected, bandpass-filtered
second signal into a value given in terms of decibels relative to
full-scale magnitude for the second signal.
66. The integrated circuit of claim 60, further comprising: a first
frequency-range isolating filter configured to receive and bandpass
filter the first signal; a first envelope detector for detecting a
signal envelope of the first signal in the bandpass filter range; a
first linear-to-decibel converter configured to convert the
envelope detected, bandpass-filtered first signal into a value
given in terms of decibels relative to full-scale magnitude for the
first signal; a second frequency-range isolating filter configured
to receive and bandpass filter the second signal; a second envelope
detector for detecting a signal envelope of the second signal in
the bandpass filter range; a second linear-to-decibel converter
configured to convert the envelope detected, bandpass-filtered
second signal into a value given in terms of decibels relative to
full-scale magnitude for the second signal; circuitry for comparing
a difference between the decibel values of the first and second
signals and comparing the difference to a threshold value and
outputting a control signal; and a proximity decision block
responsive to the control signal and configured to determine
whether the headset is on a user's ear.
67. The integrated circuit of claim 60, wherein the headset is a
wired headset for communicatively coupling to an audio device.
68. The integrated circuit of claim 60, wherein the headset is a
wireless headset for communicatively coupling to an audio
device.
69. The integrated circuit of claim 60, wherein the headset is a
pair of wireless earbuds for communicatively coupling to an audio
device.
Description
RELATED APPLICATION
[0001] The present disclosure claims priority to U.S. Provisional
patent Application Ser. No. 62/719,767, filed Aug. 20, 2018, which
is incorporated by reference herein in its entirety.
FIELD OF DISCLOSURE
[0002] The present disclosure relates in general to adaptive noise
cancellation in connection with an acoustic transducer, and more
particularly, to resetting filter coefficients of an adaptive noise
cancellation system in a manner that minimizes audible
artifacts.
BACKGROUND
[0003] Wireless telephones, such as mobile/cellular telephones,
cordless telephones, and other consumer audio devices, such as mp3
players, are in widespread use. Performance of such devices with
respect to intelligibility may be improved by providing noise
cancelling using a microphone to measure ambient acoustic events
and then using signal processing to insert an anti-noise signal
into the output of the device to cancel the ambient acoustic
events.
[0004] An active noise cancellation (ANC) system achieves the
suppression of noise by observing the ambient noise with one or
more microphones and processing the noise signal with digital
filters to generate an anti-noise signal, which is then played
through a loudspeaker. The application of active noise cancellation
to personal audio devices such as wireless telephones and
headphones is intended to enhance the users' listening experience
with respect to intelligibility and isolation from the ambient
noise. Because the acoustic environment around personal audio
devices may change depending on the noise sources that are present
and the position or fitting condition of the device itself, an
active noise cancellation system may be implemented with adaptive
filters in order to adapt the anti-noise to take such environmental
changes into account.
[0005] In many instances, it is beneficial to detect when a user
removes a headset from the user's ear(s). A pinna proximity
detector (PPD) may detect such an event. Pinna proximity detection
may have many applications and uses. For example, an audio system
may be configured to play back audio when a speaker is coupled to a
pinna and pause audio playback when the speaker is not coupled to
the pinna, to enhance user experience. As another example, an audio
system may be configured to power off a headset when not coupled to
a pinna in order to decrease power consumption and extend battery
life. Traditionally, pinna proximity detection has been performed
by playing a single low-frequency tone (e.g., 20 Hz) and measuring
the amplitude of this tone at a microphone that is located on the
headset between the speaker and the user's pinna. However, this
approach does not work well when low-frequency noise is present in
loud ambient audio environment, nor does such approach work well
when the playback audio is loud, nor does such approach work well
in an adaptive ANC system. Furthermore, this traditional solution
consumes significant power in order to transmit a low-frequency
tone continuously.
[0006] Accordingly, an approach is desired to detect an off-ear
situation reliably across all different acoustic scenarios, and to
do this in an ANC headset which presents challenges to pinna
proximity detection which a non-ANC headset does not.
SUMMARY
[0007] In accordance with the teachings of the present disclosure,
certain disadvantages and problems associated with existing
approaches to pinna proximity detection may be reduced or
eliminated.
[0008] In accordance with embodiments of the present disclosure, an
integrated circuit for implementing at least a portion of a
personal audio device may include an output for providing an output
signal to a transducer, wherein the output signal includes a pilot
signal, a microphone input for receiving a microphone signal from a
microphone indicative of an output of the transducer, and a
processing circuit. The processing circuit may be configured to
implement a pilot signal control to apply an adjustment to the
pilot signal as necessary to maintain the pilot signal at a
substantially constant magnitude regardless of proximity of the
transducer to a pinna and implement a proximity determination block
configured to determine proximity of the transducer to the pinna
based on the adjustment.
[0009] In accordance with these and embodiments of the present
disclosure, a method may include providing an output signal to a
transducer, wherein the output signal includes a pilot signal,
receiving a microphone signal from a microphone indicative of an
output of the transducer, applying an adjustment to the pilot
signal as necessary to maintain the pilot signal at a substantially
constant magnitude regardless of proximity of the transducer to a
pinna, determining proximity of the transducer to the pinna based
on the adjustment. Technical advantages of the present disclosure
may be readily apparent to one of ordinary skill in the art from
the figures, description and claims included herein. The objects
and advantages of the embodiments will be realized and achieved at
least by the elements, features, and combinations particularly
pointed out in the claims.
[0010] It is to be understood that both the foregoing general
description and the following detailed description are examples and
explanatory and are not restrictive of the claims set forth in this
disclosure.
BRIEF DESCRIPTION OF THE DRAWINGS
[0011] A more complete understanding of the present embodiments and
advantages thereof may be acquired by referring to the following
description taken in conjunction with the accompanying drawings, in
which like reference numbers indicate like features, and
wherein:
[0012] FIG. 1A is an illustration of an example wireless mobile
telephone, in accordance with embodiments of the present
disclosure;
[0013] FIG. 1B is an illustration of an example wireless mobile
telephone with a headphone assembly coupled thereto, in accordance
with embodiments of the present disclosure;
[0014] FIG. 2 is a block diagram of selected circuits within the
wireless mobile telephone depicted in FIG. 1A, in accordance with
embodiments of the present disclosure;
[0015] FIG. 3 is a block diagram of a system including selected
signal processing circuits and functional blocks within an adaptive
noise cancelling circuit and pinna proximity detection circuit of a
coder-decoder integrated circuit of FIG. 2, in accordance with
embodiments of the present disclosure;
[0016] FIG. 4 is a block diagram of the system of FIG. 3, with
additional detail showing selected functional components of a pilot
level adjustment block, in accordance with embodiments of the
present disclosure;
[0017] FIG. 5 depicts graphs of example waveforms illustrating how
a pinna proximity decision block may use a gain signal to determine
a proximity of a speaker to a pinna of an ear, in accordance with
embodiments of the present disclosure;
[0018] FIG. 6 is a block diagram of the system of FIG. 4, further
comprising a bandpass filter for isolating a sensed pilot signal,
in accordance with embodiments of the present disclosure;
[0019] FIG. 7 depicts graphs of example waveforms illustrating
operation of a pinna proximity decision block in the presence of a
source audio signal near the frequency range of a pilot signal
pilot both with bandpass filtering and without bandwidth filtering
of an error microphone signal err, in accordance with embodiments
of the present disclosure;
[0020] FIG. 8 depicts graphs of example waveforms illustrating
operation of a pinna proximity decision block having a delayed
detection of on-ear and off-ear events, in accordance with
embodiments of the present disclosure;
[0021] FIG. 9 is a block diagram of selected components of a PID
controller, in accordance with embodiments of the present
disclosure;
[0022] FIG. 10 depicts graphs of example waveforms illustrating
operation of a pinna proximity decision block in the presence of
clamping within a PID controller, in accordance with embodiments of
the present disclosure;
[0023] FIG. 11 is a block diagram of the system of FIG. 6,
depicting selected components of the system and the various control
loops present within the system, in accordance with embodiments of
the present disclosure;
[0024] FIG. 12 is a block diagram of the system of FIG. 6, further
comprising notch filters within an adaptive noise cancellation
circuit, in accordance with embodiments of the present
disclosure;
[0025] FIG. 13 is a block diagram of the system of FIG. 12, further
comprising an ambient noise estimator and a pilot reference
calculator, in accordance with embodiments of the present
disclosure;
[0026] FIG. 14 depicts a graph of an example waveform illustrating
calculation of a reference pilot signal as a function of ambient
noise, in accordance with embodiments of the present
disclosure;
[0027] FIG. 15 depicts a graph of example waveforms illustrating
calculation of proximity detection thresholds as a function of a
reference pilot signal, in accordance with embodiments of the
present disclosure;
[0028] FIG. 16 is a block diagram of the system of FIG. 6, further
comprising a programmable gain element for controlling a feedback
anti-noise gain, in accordance with embodiments of the present
disclosure;
[0029] FIGS. 17A and 17B each depict a graph of example waveforms
illustrating calculation of proximity detection thresholds as a
function of feedback anti-noise gain, in accordance with
embodiments of the present disclosure;
[0030] FIG. 18 is a block diagram of the system of FIG. 3, further
comprising circuitry for duty cycling pinna proximity detection, in
accordance with embodiments of the present disclosure;
[0031] FIG. 19 is a block diagram of the system of FIG. 18, further
comprising circuitry for pinna proximity detection based on forward
passive occlusion, in accordance with embodiments of the present
disclosure;
[0032] FIG. 20 is a block diagram of the system of FIG. 19, with
circuitry for pinna proximity detection based on reverse passive
occlusion added in lieu of circuitry for pinna proximity detection
based on forward passive occlusion, in accordance with embodiments
of the present disclosure;
[0033] FIG. 21 is a block diagram of the system of FIG. 19, with
circuitry for pinna proximity detection based on the active noise
cancellation effect added in lieu of circuitry for pinna proximity
detection based on forward passive occlusion, in accordance with
embodiments of the present disclosure;
[0034] FIG. 22 is a flow chart of an example method for selecting
and combining pinna proximity detection techniques according to
system operational parameters, in accordance with embodiments of
the present disclosure;
[0035] FIG. 23 is a block diagram of a system alternative to the
systems of the foregoing FIGURES including selected signal
processing circuits and functional blocks within an adaptive noise
cancelling circuit and pinna proximity detection circuit of a
coder-decoder integrated circuit of FIG. 2, in accordance with
embodiments of the present disclosure;
[0036] FIG. 24 is a block diagram of a system similar to that of
FIG. 24 without adaptive gain control elements, in accordance with
embodiments of the present disclosure; and
[0037] FIG. 25 is a block diagram of an example ambient noise
estimator, in accordance with embodiments of the present
disclosure.
DETAILED DESCRIPTION
[0038] The present disclosure encompasses noise cancelling
techniques and circuits that may be implemented in a personal audio
device, such as a wireless telephone. The personal audio device
includes an ANC circuit that may measure the ambient acoustic
environment and generate a signal that is injected into the speaker
(or other transducer) output to cancel ambient acoustic events. A
reference microphone may be provided to measure the ambient
acoustic environment and an error microphone may be included for
controlling the adaptation of the anti-noise signal to cancel the
ambient audio sounds and for correcting for the electro-acoustic
path from the output of the processing circuit through the
transducer.
[0039] Referring now to FIG. 1A, a personal audio device 10 as
illustrated in accordance with embodiments of the present
disclosure is shown in proximity to a human ear 5. Personal audio
device 10 is an example of a device in which techniques in
accordance with embodiments of this disclosure may be employed, but
it is understood that not all of the elements or configurations
embodied in illustrated personal audio device 10, or in the
circuits depicted in subsequent illustrations, are required in
order to practice the features recited in the claims. Personal
audio device 10 may include a transducer such as speaker SPKR that
reproduces distant speech received by personal audio device 10,
along with other local audio events such as ringtones, stored audio
program material, injection of near-end speech (i.e., the speech of
the user of personal audio device 10) to provide a balanced
conversational perception, and other audio that requires
reproduction by personal audio device 10, such as sources from
webpages or other network communications received by personal audio
device 10 and audio indications such as a low battery indication
and other system event notifications. A near-speech microphone NS
may be provided to capture near-end speech, which is transmitted
from personal audio device 10 to the other conversation
participant(s).
[0040] Personal audio device 10 may include ANC circuits and
features that inject an anti-noise signal into speaker SPKR to
improve intelligibility of the distant speech and other audio
reproduced by speaker SPKR. A reference microphone R may be
provided for measuring the ambient acoustic environment, and may be
positioned away from the typical position of a user's mouth, so
that the near-end speech may be minimized in the signal produced by
reference microphone R. Another microphone, error microphone E, may
be provided in order to further improve the ANC operation by
providing a measure of the ambient audio combined with the audio
reproduced by speaker SPKR close to ear 5, when personal audio
device 10 is in close proximity to ear 5. In some embodiments,
additional reference and/or error microphones may be employed. In
yet other embodiments, an ANC system may include error microphone
E, but no reference microphone R.
[0041] Circuit 14 within personal audio device 10 may include an
audio CODEC integrated circuit (IC) 20 that receives the signals
from reference microphone R, near-speech microphone NS, and error
microphone E and interfaces with other integrated circuits such as
a radio-frequency (RF) integrated circuit 12 having a wireless
telephone transceiver. In some embodiments of the disclosure, the
circuits and techniques disclosed herein may be incorporated in a
single integrated circuit that includes control circuits and other
functionality for implementing the entirety of the personal audio
device, such as an MP3 player-on-a-chip integrated circuit. In
these and other embodiments, the circuits and techniques disclosed
herein may be implemented partially or fully in software and/or
firmware embodied in computer-readable media and executable by a
controller or other processing device.
[0042] In general, ANC techniques of the present disclosure may
measure ambient acoustic events (as opposed to the output of
speaker SPKR and/or the near-end speech) impinging on reference
microphone R (in embodiments in which reference microphone R is
present), and by also measuring the same ambient acoustic events
impinging on error microphone E, ANC processing circuits of
personal audio device 10 adapt an anti-noise signal generated from
the output of reference microphone R to have a characteristic that
minimizes the amplitude of the ambient acoustic events at error
microphone E. Because acoustic path P(z) extends from reference
microphone R to error microphone E, ANC circuits may effectively
estimate acoustic path P(z) while removing effects of an
electro-acoustic path S(z) that represents the response of the
audio output circuits of CODEC IC 20 and the acoustic/electric
transfer function of speaker SPKR including the coupling between
speaker SPKR and error microphone E in the particular acoustic
environment, which may be affected by the proximity and structure
of ear 5 and other physical objects and human head structures that
may be in proximity to personal audio device 10, when personal
audio device 10 is not firmly pressed to ear 5. While the
illustrated personal audio device 10 includes a two-microphone ANC
system with a third near-speech microphone NS, some aspects of the
present disclosure may be practiced in a system that does not
include separate error and reference microphones, or a wireless
telephone that uses near-speech microphone NS to perform the
function of the reference microphone R. Also, in personal audio
devices designed only for audio playback, near-speech microphone NS
will generally not be included, and the near-speech signal paths in
the circuits described in further detail below may be omitted,
without changing the scope of the disclosure, other than to limit
the options provided for input to the microphone.
[0043] Referring now to FIG. 1B, personal audio device 10 is
depicted having a headphone assembly 13 coupled to it via audio
port 15. Audio port 15 may be communicatively coupled to RF
integrated circuit 12 and/or CODEC IC 20, thus permitting
communication between components of headphone assembly 13 and one
or more of RF integrated circuit 12 and/or CODEC IC 20. As shown in
FIG. 1B, headphone assembly 13 may include a combox 16, a left
headphone 18A, and a right headphone 18B. In some embodiments,
headphone assembly 13 may comprise a wireless headphone assembly,
in which case all or some portions of CODEC IC 20 may be present in
headphone assembly 13, and headphone assembly 13 may include a
wireless communication interface (e.g., BLUETOOTH) in order to
communicate between headphone assembly 13 and personal audio device
10.
[0044] As used in this disclosure, the term "headphone" broadly
includes any loudspeaker and structure associated therewith that is
intended to be mechanically held in place proximate to a listener's
ear canal, and includes without limitation earphones, earbuds, and
other similar devices. As more specific examples, "headphone" may
refer to intra-concha earphones, supra-concha earphones, and
supra-aural earphones.
[0045] Combox 16 or another portion of headphone assembly 13 may
have a near-speech microphone NS to capture near-end speech in
addition to or in lieu of near-speech microphone NS of personal
audio device 10. In addition, each headphone 18A, 18B may include a
transducer such as speaker SPKR that reproduces distant speech
received by personal audio device 10, along with other local audio
events such as ringtones, stored audio program material, injection
of near-end speech (i.e., the speech of the user of personal audio
device 10) to provide a balanced conversational perception, and
other audio that requires reproduction by personal audio device 10,
such as sources from webpages or other network communications
received by personal audio device 10 and audio indications such as
a low battery indication and other system event notifications. Each
headphone 18A, 18B may include a reference microphone R for
measuring the ambient acoustic environment and an error microphone
E for measuring of the ambient audio combined with the audio
reproduced by speaker SPKR close to a listener's ear when such
headphone 18A, 18B is engaged with the listener's ear. In some
embodiments, CODEC IC 20 may receive the signals from reference
microphone R and error microphone E of each headphone and
near-speech microphone NS, and perform adaptive noise cancellation
for each headphone as described herein. In other embodiments, a
CODEC IC or another circuit may be present within headphone
assembly 13, communicatively coupled to reference microphone R,
near-speech microphone NS, and error microphone E, and configured
to perform adaptive noise cancellation as described herein. As in
FIG. 1A, in some embodiments the configuration shown in FIG. 1B may
include error microphones E, but no reference microphones R.
[0046] Referring now to FIG. 2, selected circuits within personal
audio device 10 are shown in a block diagram, which in other
embodiments may be placed in whole or in part in other locations
such as one or more headphones or earbuds. In embodiments in which
a reference microphone R is present, CODEC IC 20 may include an
analog-to-digital converter (ADC) 21A for receiving the reference
microphone signal from microphone R and generating a digital
representation ref of the reference microphone signal. CODEC IC 20
may also include an ADC 21B for receiving the error microphone
signal from error microphone E and generating a digital
representation err of the error microphone signal, and an ADC 21C
for receiving the near speech microphone signal from near speech
microphone NS and generating a digital representation ns of the
near speech microphone signal. CODEC IC 20 may generate an output
for driving speaker SPKR from an amplifier A1, which may amplify
the output of a digital-to-analog converter (DAC) 23 that receives
the output of a combiner 26. Combiner 26 may combine audio signals
is from internal audio sources 24, a pilot signal PILOT generated
by pinna proximity detector (PPD) 32, the anti-noise signal
generated by ANC circuit 30, which by convention has the same
polarity as the noise in reference microphone signal ref and is
therefore subtracted by combiner 26, and a portion of near speech
microphone signal ns so that the user of personal audio device 10
may hear his or her own voice in proper relation to downlink speech
ds, which may be received from radio frequency (RF) integrated
circuit 22 and may also be combined by combiner 26. Near speech
microphone signal ns may also be provided to RF integrated circuit
22 and may be transmitted as uplink speech to the service provider
via antenna ANT.
[0047] Referring now to FIG. 3, details of a system 40 including
selected components of CODEC IC 20, including ANC circuit 30 and
PPD 32, are shown in accordance with embodiments of the present
disclosure. ANC circuit 30 as shown in FIG. 3 does not include an
input for a reference microphone signal, and thus, relies on
feedback ANC based on an error microphone signal from error
microphone E.
[0048] ANC circuit 30 may include an adaptive filter 34 to estimate
the response of path S(z), which may have coefficients controlled
by SE coefficient control block 33 that may compare a source audio
signal (e.g., downlink audio signal ds and/or internal audio signal
ia) and a playback-corrected error signal PBCE to generate such
coefficients. Playback corrected error signal PBCE may include
error microphone signal err after removal of the source audio
signal downlink audio signal ds and/or internal audio signal ia,
that has been filtered by adaptive filter 34 to represent the
expected downlink audio delivered to error microphone E, and which
is removed from the output of adaptive filter 34 by a combiner 36
to generate playback-corrected error signal PBCE. SE coefficient
control block 33 may correlate the source audio signal (e.g.,
actual downlink speech signal ds and/or internal audio signal ia)
with the components of the source audio signal. In operation, SE
coefficient control block 33 may implement an adaptive algorithm,
such as a least-means-square algorithm, which may accept the source
audio signal as a training signal and playback-corrected error
signal PBCE as another input, and may adapt coefficients of
adaptive filter 34 in an attempt to minimize playback-corrected
error signal PBCE (e.g., in a mean-square sense). In the process of
minimizing playback-corrected error signal PBCE, adaptive filter 34
may approach the transfer function of the electro-acoustic path
S(z), which may be a function of coupling between speaker SPKR and
the pinna of ear 5. Thus, adaptive filter 34 and SE coefficient
control block 33 in effect implement an adaptive speaker-to-pinna
model to aid the feedback loop including feedback filter 44 to not
cancel the playback audio, but rather to cancel only the ambient
noise that makes its way through the headset and to the inside of
the pinna of ear 5, as observed by error microphone E.
[0049] Adaptive filter 34 may thereby be adapted to generate a
signal from the source audio signal, that when subtracted from
error microphone signal err, includes the content of error
microphone signal err that is not due to the source audio signal in
order to generate playback-correct error signal PBCE.
[0050] In FIG. 3, the function of combiner 26 of FIG. 2 is
performed by combiners 26A and 26B. Combiner 26A may combine the
source audio signal (e.g., downlink audio signal ds and/or internal
audio signal ia) with pilot signal PILOT generated by PPD 32. It is
such source audio signal as combined with pilot signal PILOT that
may be processed by ANC circuit 30. Combiner 26B may combine the
resulting signal of combiner 26A with anti-noise signal ANTI-NOISE
to generate an audio output signal to be played back to speaker
SPKR.
[0051] As depicted in FIG. 3, ANC circuit 30 may also comprise
feedback filter 44. Feedback filter 44 may receive the playback
corrected error signal PBCE and may apply a response FB(z) to
generate a feedback anti-noise signal ANTI-NOISE based on the
playback corrected error. Feedback signal ANTI-NOISE may be
combined by combiner 26B with the source audio signal and pilot
signal PILOT to be reproduced by speaker SPKR.
[0052] Pinna proximity detection performed by PPD 32 may begin with
a pilot signal generator 52 generating a raw pilot signal, which
may include a single low-frequency tone, a group of tones, or a
narrow band of non-playback audio having amplitude changes
significant enough when speaker SPKR is near the pinna as opposed
to away from the pinna. A gain element 54 may apply a gain to the
raw pilot signal to generate an ideally human-inaudible pilot
signal PILOT that may be combined with the source audio signal via
combiner 26A and subsequently added to anti-noise signal ANTI-NOISE
via combiner 26B. The resulting audio output signal, including
pilot signal PILOT, may be converted into the analog domain by DAC
23, amplified by amplifier A1, and reproduced by speaker SPKR.
Error microphone E may receive the combined acoustic signal
reproduced by speaker SPKR (which may include pilot signal PILOT),
and after conversion of the combined acoustic signal into the
digital domain to generate error microphone signal err, a pilot
tracker 56 of PPD 32 may isolate pilot signal PILOT from error
microphone signal err to generate sensed pilot signal PILOT'.
[0053] A pilot level adjustment block 58 may receive sensed pilot
signal PILOT' and generate a gain control signal GAIN to control a
gain of gain element 54 in order to maintain sensed pilot signal
PILOT' at a predetermined constant level. A pinna proximity
decision block 60 may receive the gain control signal GAIN
generated by pilot level adjustment block 58 and compare the gain
indicated by gain control signal GAIN to a gain needed to maintain
a constant pilot level when speaker SPKR is not near the pinna of
ear 5. Based on such comparison, pinna proximity decision block 60
may determine a proximity between the pinna of ear 5 and speaker
SPKR. To illustrate, when speaker SPKR is near the pinna, an
acoustic load allows speaker SPKR to efficiently drive pilot signal
PILOT, and gain element 54 does not need to provide much (if any)
gain to maintain the pilot level at a desired predetermined level.
However, when speaker SPKR is not near the pinna, the acoustic load
is different and speaker SPKR may be inefficient, meaning gain
element 54 must provide more gain in order to preserve the desired
predetermined level of pilot signal PILOT as observed at error
microphone E.
[0054] FIG. 4 is a block diagram of the system 40 depicted in FIG.
3, with additional detail showing selected functional components of
pilot level adjustment block 58, in accordance with embodiments of
the present disclosure. Pilot level adjustment block 58 may
implement a proportional-integral-derivative (PID) based adaptive
gain control (AGC) loop to automatically and robustly maintain a
constant pilot level.
[0055] To protect the AGC loop of pilot level adjustment block 58
from direct-current signal components that may falsely driver PID
control, a high-pass filter 62 (e.g., with a cutoff frequency of
one-tenth of the center of pilot signal PILOT), may filter out
low-frequency components of pilot signal PILOT.
[0056] In addition, the high-pass filtered pilot signal PILOT may
be decimated by decimator 64, to allow the AGC loop of pilot level
adjustment block 58 to be operated at a significantly reduced rate,
which may reduce processing requirements of the AGC loop.
[0057] Pilot level adjustment block 58 may include a
linear-to-decibel converter 66 to convert sensed pilot signal
PILOT' into a value PILOT.sub.dB' given in terms of decibels
relative to full-scale magnitude for sensed pilot signal PILOT'.
Operation in the decibel domain may enable for compression of the
dynamic range of pilot signal PILOT and preservation of the signal
for a reasonable number of fixed-point bits.
[0058] A combiner 68 may subtract a reference pilot signal
PILOT.sub.REF from sensed pilot signal PILOT.sub.dB' to generate an
error signal ERROR. A PID controller 70 may receive the error
signal and generate a gain signal GAIN.sub.dB in decibels based on
the error signal in order to adaptively minimize error signal
ERROR. A decibel-to-linear converter 72 may convert the
decibel-domain gain signal GAIN.sub.dB into a linear scale
equivalent, and such converted linear scale equivalent may be
interpolated by interpolator 74 to have the same sample frequency
as ADC 21B, in order to generate gain signal GAIN.
[0059] FIG. 5 depicts graphs of example waveforms illustrating how
pinna proximity decision block 60 may use decibel-domain gain
signal GAIN.sub.dB to determine a proximity of speaker SPKR to the
pinna of ear 5, in accordance with embodiments of the present
disclosure. The top waveform of FIG. 5 depicts decibel-domain gain
signal GAIN.sub.dB versus time for a time period, the beginning of
which a user has a headset on ear, then removes it briefly, then
places it back on ear. Pinna decision proximity block 60 may
determine whether speaker SPKR is on ear or off ear by comparing
decibel-domain gain signal GAIN.sub.dB to a pair of thresholds: (i)
speaker SPKR may be declared "on ear" when decibel-domain gain
signal GAIN.sub.dB exceeds an upper threshold; and (ii) speaker
SPKR may be declared "off ear" when decibel-domain gain signal
GAIN.sub.dB falls below a lower threshold.
[0060] FIG. 6 is a block diagram of system 40 as shown in FIG. 4,
further comprising a bandpass filter 76 for isolating sensed pilot
signal PILOT' from the source audio signal, in accordance with
embodiments of the present disclosure. Because source audio
reproduced by speaker SPKR and captured by error microphone E may
have signal content near the frequency region of pilot signal
PILOT, bandpass filter 76 may filter error microphone signal err in
a frequency range near the frequency region of pilot signal PILOT,
in order to minimize the influence of the source audio signal on
the functionality of PPD 32, and in order to allow pilot tracker 56
to focus on pilot signal PILOT. FIG. 7 depicts graphs of example
waveforms illustrating operation of pinna proximity decision block
60 in the presence of a source audio signal near the frequency
range of pilot signal pilot both with bandpass filtering and
without bandpass filtering of error microphone signal err, in
accordance with embodiments of the present disclosure. As shown in
FIG. 7, without bandpass filtering of error microphone signal err,
pinna proximity detector block 60 may have difficulty in
distinguishing sensed pilot signal PILOT' from the source audio
signal, and may be able to effectively track sensed pilot signal
PILOT' with bandpass filtering of error microphone signal err.
[0061] As speaker SPKR is pulled away from the pinna of ear 5,
often there is a brief moment in time when the headset comprising
speaker SPKR forms a tighter seal, and the speaker forms an even
stronger acoustic coupling to error microphone E. In this case, the
gain needed within gain element 54 to maintain pilot signal PILOT
at a desired level may be exceedingly small. Similarly, when the
headset comprising speaker SPKR is again pushed back onto ear 5, a
tighter seal may be briefly formed. In these cases, PPD 32 may take
longer to make the correct decision regarding proximity of speaker
SPKR to pinna of ear 5 because gain signal GAIN may be temporarily
pushed further away from the value at which it will settle, and
thus pushed away from the threshold it must cross to indicate an
off-ear event. FIG. 8 depicts graphs of example waveforms
illustrating this phenomenon, in accordance with embodiments of the
present disclosure.
[0062] To mitigate this phenomenon, PID controller 70 may include
features, in particular a signal clamp, not present in a typical
PID controller. FIG. 9 is a block diagram of selected components of
PID controller 70, in accordance with embodiments of the present
disclosure. As shown in FIG. 9, a clamp 78 may be added to an
integral component of a typical PID controller, such that if an
input signal INPUT falls below a threshold value CLAMP_THRESHOLD,
an output signal OUTPUT of PID controller 70 (which may correspond
to decibel-domain gain signal GAIN.sub.dB) is maintained at the
level of CLAMP_THRESHOLD, as depicted in FIG. 10. As shown in FIG.
10, the clamped decibel-domain gain signal GAIN.sub.dB may enable
reduced settling time at the off-ear value of decibel-domain gain
signal GAIN.sub.dB as compared to if decibel-domain gain signal
GAIN.sub.dB was unclamped, as shown in FIG. 8, thus enabling
quicker detection of off-ear and on-ear events.
[0063] FIG. 11 is a block diagram of system 40 as shown in FIG. 6,
depicting selected components of system 40 and the various control
loops present within the system, in accordance with embodiments of
the present disclosure. In particular, FIG. 11 depicts a
speaker-to-error microphone modeling loop, an anti-noise feedback
loop, and an adaptive gain control loop. Some components of system
40 present in FIG. 6 are not shown in FIG. 11, for the purposes of
clarity and exposition.
[0064] It may be desirable that the level of pilot signal PILOT be
controlled only by the adaptive gain control of PPD 32. However,
the level of pilot signal PILOT as seen by error microphone E may
also be affected by the interaction of the anti-noise feedback loop
and the speaker-to-error microphone modeling loop. As the adaptive
speaker-to-error microphone modeling loop attempts to model the
acoustic coupling between speaker SPKR and error microphone E, it
may do a very poor job of such modeling at low frequencies in a
narrow band near that of pilot signal PILOT. This poor modeling in
turn may cause the pilot signal at the output of combiner 36 to
vary significantly. This varying remnant of pilot signal PILOT may
end up within a feedback loop, where it may be cancelled or boosted
in a varying manner as it is reproduced by speaker SPKR and is
sensed by error microphone E. The AGC loop, in turn, may attempt to
automatically adjust the level of pilot signal PILOT. In this case,
the AGC loop may not be the sole mechanism controlling pilot signal
PILOT, and the AGC loop may accordingly overcompensate or
undercompensate, and the AGC loop may become unstable. As a result,
not only may PPD 32 make an incorrect decision, but also the
adaptive speaker-to-error microphone modeling loop may adapt to a
strong pilot signal, and the mis-adaptation that results may cause
the adaptive speaker-to-error microphone modeling loop to also
become unstable.
[0065] To mitigate this problem, a band-rejection or notch filter
80A with response SE_NOTCH(z) and centered on the center frequency
of pilot signal PILOT may be added at the output of adaptive filter
34 as shown in FIG. 12. In addition, due to least-mean-squares
stability criteria, an equivalent phase effect of notch filter 80A
should be placed inline with the training signal input to SE
coefficient control block 33, and thus a copy 80B of notch filter
80A may be placed prior to the training signal input of SE
coefficient control block 33. With the presence of notch filters
80A and 80B as shown in FIG. 12, the adaptive speaker-to-error
microphone modeling loop and the anti-noise feedback loop may not
interact to change the level of pilot signal PILOT, and only the
AGC loop implemented by PPD 32 may control the level of pilot
signal PILOT. Accordingly, the level of pilot signal PILOT may only
change in response to changes in the speaker-to-error microphone
coupling as a headset is adjusted on or off the pinna of ear 5.
Furthermore, the adaptive speaker-to-error microphone loop may not
adapt to pilot signal PILOT itself, as pilot signal PILOT is not
part of the speaker-to-error microphone loop's training signal.
[0066] In the case when the ambient noise (e.g., outside a headset
comprising speaker SPKR) is loud, pilot tracker 56 may struggle to
follow the pilot signal, and thus PPD 32 may make incorrect
decisions regarding the proximity of speaker SPKR to pinna of ear
5. To solve this problem, as shown in FIG. 13, an ambient noise
estimator 82 of PPD 32 may estimate an amount of ambient noise
present in the sensed pilot signal PILOT'. Approaches to generating
an estimate of ambient noise are described elsewhere in this
disclosure. Based on the amount of ambient noise present in sensed
pilot signal PILOT', a pilot reference calculator 84 of PPD 32 may
determine the reference pilot signal PILOT.sub.REF. For example, in
some embodiments, once the ambient noise has increased beyond a
minimum noise threshold, reference pilot signal PILOT.sub.REF may
be increased decibel-per-decibel along with increasing ambient
noise, for example as shown in FIG. 14. In addition, pinna
proximity decision block 60 may be configured to modify decision
thresholds for detecting off-ear and on-ear events to account for
the fact that any increase in gain signal GAIN will be at least
partly caused by increase in reference pilot signal PILOT.sub.REF,
for example as shown in FIG. 15.
[0067] FIG. 16 is a block diagram of the system of FIG. 6, further
comprising a programmable gain element 46 for controlling a
programmable feedback anti-noise gain, in accordance with
embodiments of the present disclosure. As depicted in FIG. 16, a
path of the feedback anti-noise may have a programmable gain
element 46 in series with feedback filter 44 such that the product
of response FB(z) and a gain of programmable gain element 46 is
applied to playback corrected error signal PBCE in order to
generate anti-noise signal ANTI-NOISE. The gain of programmable
gain element 46 may be modified according to user settings input by
a user of personal audio device 10. Although feedback filter 44 and
gain element 46 are shown as separate components of ANC circuit 30,
in some embodiments some structure and/or function of feedback
filter 44 and gain element 46 may be combined. For example, in some
of such embodiments, an effective gain of feedback filter 44 may be
varied via control of one or more filter coefficients of feedback
filter 44. To the extent that gain element 46 has variable gain,
feedback filter 44 in combination with gain element 46 may be
considered an adaptive filter wherein the gain of gain element 46
is analogous to filter coefficients of feedback filter 44.
[0068] The varying anti-noise resulting from varying the
programmable feedback anti-noise gain may affect the level of pilot
signal PILOT detected at error microphone E by either partially
cancelling pilot signal PILOT and/or amplifying pilot signal PILOT.
Because the programmable feedback anti-noise gain may be modified
by a user and may not be anticipated at product design time, pinna
proximity decision block 60 may dynamically compensate for the
programmable feedback anti-noise gain in order to make the correct
speaker-to-ear proximity decision regardless of the programmable
feedback anti-noise gain, as shown by the programmable feedback
gain being communicated to pinna proximity decision block 60, as
shown in FIG. 16.
[0069] Adjusting the proximity detection thresholds used by pinna
proximity decision block 60 responsive to changes to the
programmable feedback anti-noise gain may be based on whether
increasing the programmable feedback anti-noise gain partially
cancels or boosts pilot signal PILOT. For example, at product
design time of personal audio device 10, testing equipment may
measure how much effect (if any) the anti-noise feedback loop has
on pilot signal PILOT when the programmable feedback anti-noise
gain is set to its maximum. In the case that the anti-noise
feedback loop partially cancels pilot signal PILOT, decision
thresholds of pinna proximity decision block 60 may increase with
increasing the programmable feedback anti-noise gain, as shown in
FIG. 17A. On the other hand, in the case that the anti-noise
feedback loop partially boosts pilot signal PILOT, decision
thresholds of pinna proximity decision block 60 may decrease with
increasing programmable feedback anti-noise gain, as shown in FIG.
17B.
[0070] FIG. 18 is a block diagram of system 40 as shown in FIG. 3,
further comprising circuitry for duty cycling pinna proximity
detection, in accordance with embodiments of the present
disclosure. In cases in which there is no playback audio and no
anti-noise, it may remain desirable to use PPD 32. However, to
reduce power consumption and maximize battery life, it may be
desirable to duty cycle functionality of PPD 32.
[0071] As shown in FIG. 18, PPD 32 may include a ramp scaler 86 and
a duty-cycle timer 88. In operation, duty-cycle timer 88 may go
active for a brief amount of time at regular intervals (e.g., is
active for one second out of each ten second period). Duty-cycle
timer 88 may generate control signals for enabling operation of
pilot level adjustment block 58 (indicated by "Adjustment Enable"
in FIG. 18), enabling operation of pinna proximity decision block
60 (indicated by "Decision Enable" in FIG. 18), and enabling
operation of ramp scaler 86 (indicated by "Ramp Enable" in FIG.
18). Thus, as shown in the waveforms depicted at the bottom of FIG.
18, when duty-cycle timer 88 is active, it may enable operation of
pilot level adjustment block 58, pinna proximity decision block 60,
and ramp scaler 86. When enabled, ramp scaler 86 may, at the
beginning of each duty cycle active period, ramp a gain to be
applied to the signal generated by pilot signal generator 52 from a
minimum gain (e.g., zero) to a maximum gain (e.g., unity), and at
the end of each duty cycle active period, ramp a gain to be applied
to the signal generated by pilot signal generator 52 from the
maximum gain to the minimum gain. Such ramping may minimize the
occurrence of audio artifacts caused by application of the periodic
pilot signal.
[0072] During the durations in which ramp scaler 86 is ramping up
and ramping down its gain, the AGC loop of PPD 32 is not
responsible for the pilot level, and thus pinna proximity detection
should be frozen, and adjustments to the pilot level should be
disabled, as shown in FIG. 18. When pilot signal PILOT is muted by
ramp scaler 86, the most recent proximity decision may be held
until the next active period of duty-cycle timer 88.
[0073] Accordingly, pilot signal PILOT may be non-zero for a brief
amount of time at regular intervals, and power savings may be
achieved by not having the drive amplifier A1 and speaker SPKR with
a continuous signal.
[0074] FIG. 19 is a block diagram of system 40 as shown in FIG. 18,
further comprising circuitry for pinna proximity detection based on
forward passive occlusion, in accordance with embodiments of the
present disclosure. As mentioned above in reference to FIGS. 1A,
1B, and 2, personal audio device 10 may include a reference
microphone for sensing ambient sound. The addition of reference
microphone R to system 40 may enable an additional pinna proximity
detection by a technique known as forward passive occlusion. By
comparing the sound energies in a specific frequency band at both
reference microphone R and error microphone E, PPD 32 may take
advantage of physical properties of a headset (e.g., headphone 18A,
18B of FIG. 1B) and the fact that higher frequencies (e.g., in the
band from 2 KHz to 5 KHz) may show a significant difference when
the headset is on ear (due to the sound-blocking effect of the
headset) and off ear. This extra information may be used in lieu of
the pilot signal-based decision, or it may supplement the pilot
signal-based decision to build more confidence in the final
decision.
[0075] As shown in FIG. 19, PPD 32 may also include a
frequency-range isolating filter 90 configured to receive and
bandpass filter reference microphone signal ref, an envelope
detector 92 for detecting a signal envelope of reference microphone
signal ref in the bandpass filter range, and a linear-to-decibel
converter 94 configured to convert the envelope detected,
bandpass-filtered reference microphone signal into a value
REF.sub.dB given in terms of decibels relative to full-scale
magnitude for reference microphone signal ref. Similarly, PPD 32
may also include a frequency-range isolating filter 96 configured
to receive and bandpass filter error microphone signal err, an
envelope detector 98 for detecting a signal envelope of error
microphone signal err in the bandpass filter range, and a
linear-to-decibel converter 100 configured to convert the envelope
detected, bandpass-filtered error microphone signal into a value
ERR.sub.dB given in terms of decibels relative to full-scale
magnitude for error microphone signal err. A supplementary decision
block 102 may compare a difference between value REF.sub.dB and
ERR.sub.dB, compare such difference to a threshold TH_FPO, and
communicate a signal to pinna proximity decision block 60 that may
override or supplement the proximity decision made by pinna
proximity decision block 60.
[0076] FIG. 20 is a block diagram of system 40 as shown in FIG. 19,
with circuitry for pinna proximity detection based on reverse
passive occlusion added in lieu of circuitry for pinna proximity
detection based on forward passive occlusion, in accordance with
embodiments of the present disclosure. Presence of reference
microphone R in system 40 may enable an additional pinna proximity
detection by a technique known as reverse passive occlusion. By
comparing the sound energies in a specific frequency band at both
reference microphone R and error microphone E, PPD 32 may take
advantage of physical properties of a headset (e.g., headphone 18A,
18B of FIG. 1B) and the fact that lower frequencies (e.g., below
100 Hz) may show a significant difference when the headset is on
ear (e.g., due to bone conduction resulting jaw movement, joint
vibrations within a head due to neck movement) and off ear. For
instance, error microphone E may receive bone conduction effects
while reference microphone R may not, and bone conduction effects
may only occur during an on-ear condition. Accordingly, this extra
information may be used in lieu of the pilot signal-based decision
and/or forward passive occlusion-based decision, or it may
supplement the pilot signal-based decision and/or forward passive
occlusion-based decision to build more confidence in the final
decision.
[0077] As shown in FIG. 20, PPD 32 may also include a
frequency-range isolating filter 104 configured to receive and
low-pass filter reference microphone signal ref, an envelope
detector 106 for detecting a signal envelope of reference
microphone signal ref in the low-pass filter range, and a
linear-to-decibel converter 108 configured to convert the envelope
detected, low-pass-filtered reference microphone signal into a
value REF.sub.dB given in terms of decibels relative to full-scale
magnitude for reference microphone signal ref. Similarly, PPD 32
may also include a frequency-range isolating filter 110 configured
to receive and low-pass filter error microphone signal err, an
envelope detector 112 for detecting a signal envelope of error
microphone signal err in the low-pass filter range, and a
linear-to-decibel converter 114 configured to convert the envelope
detected, low-pass-filtered error microphone signal into a value
ERR.sub.dB given in terms of decibels relative to full-scale
magnitude for error microphone signal err. A supplementary decision
block 116 may compare a difference between value REF.sub.dB and
ERR.sub.dB, compare such difference to a threshold TH_RPO, and
communicate a signal to pinna proximity decision block 60 that may
override or supplement the proximity decision made by pinna
proximity decision block 60 and/or supplementary decision block
102.
[0078] FIG. 21 is a block diagram of system 40 as shown in FIG. 19,
with circuitry for pinna proximity detection based on active noise
cancellation effect added in lieu of circuitry for pinna proximity
detection based on forward passive occlusion, in accordance with
embodiments of the present disclosure. Presence of reference
microphone R in system 40 may enable an additional pinna proximity
detection by a technique known as the active noise cancellation
effect. By comparing the sound energies in a specific frequency
band at both reference microphone R and error microphone E, PPD 32
may take advantage of physical properties of a headset (e.g.,
headphone 18A, 18B of FIG. 1B) and the fact that middle frequencies
(e.g., from 300 Hz to 2 KHz) may show a significant difference when
the headset is on ear (e.g., due to active noise cancellation
effects) and off ear. Accordingly, this extra information may be
used in lieu of the pilot signal-based decision, forward passive
occlusion-based decision, and/or reverse passive occlusion-based
decision, or it may supplement the pilot signal-based decision,
forward passive occlusion-based decision, and/or reverse passive
occlusion-based decision to build more confidence in the final
decision.
[0079] As shown in FIG. 21, PPD 32 may also include a
frequency-range isolating filter 118 configured to receive and
bandpass filter reference microphone signal ref, an envelope
detector 120 for detecting a signal envelope of reference
microphone signal ref in the bandpass filter range, and a
linear-to-decibel converter 122 configured to convert the envelope
detected, bandpass-filtered reference microphone signal into a
value REF.sub.dB given in terms of decibels relative to full-scale
magnitude for reference microphone signal ref. Similarly, PPD 32
may also include a frequency-range isolating filter 124 configured
to receive and bandpass filter error microphone signal err, an
envelope detector 126 for detecting a signal envelope of error
microphone signal err in the bandpass filter range, and a
linear-to-decibel converter 128 configured to convert the envelope
detected, bandpass-filtered error microphone signal into a value
ERR.sub.dB given in terms of decibels relative to full-scale
magnitude for error microphone signal err. A supplementary decision
block 130 may compare a difference between value REF.sub.dB and
ERR.sub.dB, compare such difference to a threshold TH_ANCE, and
communicate a signal to pinna proximity decision block 60 that may
override or supplement the proximity decision made by pinna
proximity decision block 60, supplementary decision block 102,
and/or supplementary decision block 116.
[0080] By employing multiple pinna proximity methods (pilot
signal-based, forward passive occlusion, reverse passive occlusion,
and active noise cancellation effect) according to the ambient
and/or listening scenario (e.g., whether source audio is present or
not, whether ANC is ON or not), PPD 32 may use the best detector
for the scenario. Furthermore, PPD 32 may combine detector
decisions to a product for a potentially more robust pinna
proximity decision. FIG. 22 is a flow chart of an example method
132 for selecting and combining pinna proximity detection
techniques according to system operational parameters, in
accordance with embodiments of the present disclosure. In some
embodiments, method 132 may be executed by pinna proximity decision
block 60 or another component of PPD 32.
[0081] Method 132 may start at step 134, in which PPD 32 may
determine if a source audio signal is present. If a source audio
signal is present, method 132 may proceed to step 146. If no source
audio signal is present, method 132 may proceed to step 136.
[0082] At step 136, PPD 32 may determine if ambient sound has
content at higher frequencies (e.g., between 2 KHz and 5 kHz). If
ambient sound has content at higher frequencies, method 132 may
proceed to step 138. Otherwise, if ambient sound does not have
content at higher frequencies, method 132 may proceed to step
140.
[0083] At step 138, PPD 32 may activate forward passive occlusion
detection. After completion of step 138, method 132 may proceed to
step 148.
[0084] At step 140, PPD 32 may determine whether adaptive noise
cancellation is active in system 40. If adaptive noise cancellation
is active, method 132 may proceed to step 142. If adaptive noise
cancellation is inactive, method 132 may proceed to step 146.
[0085] At step 142, PPD 32 may determine if ambient sound has
content at middle frequencies (e.g., between 300 Hz and 2 kHz). If
ambient sound has content at middle frequencies, method 132 may
proceed to step 144. Otherwise, if ambient sound does not have
content at middle frequencies, method 132 may proceed to step
146.
[0086] At step 144, PPD 32 may activate active noise cancellation
effect detection. After completion of step 144, method 132 may
proceed to step 148.
[0087] At step 146, PPD 32 may activate pilot signal-based
detection. After completion of step 146, method 132 may proceed to
step 148.
[0088] At step 148, PPD 32 may activate reverse passive occlusion
detection. After completion of step 148, method 132 may proceed to
step 150.
[0089] At step 150, PPD 32 may combine the detector decisions of
the activated proximity detection methods to render a pinna
proximity detection decision. After completion of step 150, method
132 may end.
[0090] In addition to the approach described above for selecting
and combining pinna proximity detection methods, other parameters
may be used to select which pinna proximity detection methods to
employ. For example, some detection methods may consume more
battery power than others (e.g., when a pilot detector plays a
strong pilot in a case where there is no source audio or
anti-noise, such approach consumes a fair amount of power to drive
pilot signal PILOT through speaker SPKR). In such case, if there is
another detection approach well-suited to the ambient/listening
scenario, PPD 32 may select it instead.
[0091] FIG. 23 is a block diagram of a system 40A including
selected components of CODEC IC 20, including ANC circuit 30 and
PPD 32A, in accordance with embodiments of the present disclosure.
System 40A of FIG. 23 is similar in many respects to system 40 of
FIG. 3, and thus, only the key differences between systems 40A and
40 are described below. One key difference between system 40A and
system 40 is that system 40A includes PPD 32A in lieu of PPD 32.
Unlike PPD 32, PPD 32A may perform pinna proximity detection
without use of a pilot signal. Instead, when source audio is
present, the source audio signal may provide the training signal
for an adaptive gain-based pinna proximity detector. As shown in
FIG. 23, PPD 32A may include low-pass filters 152 and 154. Low-pass
filters 152 and 154 may respectively low-pass filter error
microphone signal err and the source audio signal in order to focus
on analysis on the lower-frequency response of acoustic coupling
between speaker SPKR and error microphone E. PPD 32A may also
include two filters 156 and 158, each having a response S_OE_LP(z)
that may represent an a priori low-frequency speaker SPKR to error
microphone E coupling when a headphone is not near pinna of ear 5
(off ear). Filter 158 may be needed to maintain phase balance for
both inputs to gain control block 160.
[0092] A gain control block 160 (which may use a least-mean-squares
approach) may adaptively control a gain of a gain element 162 in an
attempt to minimize a difference signal (as generated by combiner
164) between the low-pass filtered error microphone signal and the
output of filter 156. When the output of combiner 164 is minimized,
the combination of the adaptive gain of gain element 162 and filter
158 may adequately model a low-frequency coupling response between
speaker SPKR and error microphone E. When speaker SPKR is off-ear,
this gain may be near unity. When speaker SPKR is on ear, this gain
may be much smaller than unity. Pinna proximity decision block 60A
may use this gain to make a decision regarding proximity between
speaker SPKR and pinna of ear 5.
[0093] When source audio is available, proximity detection may be
performed by removing adaptive gain-based components from PPD 32A.
FIG. 24 is a block diagram of a system 40B including selected
components of CODEC IC 20, including ANC circuit 30 and PPD 32B, in
accordance with embodiments of the present disclosure. System 40B
of FIG. 24 is similar in many respects to system 40A of FIG. 23,
and thus, only the key differences between systems 40B and 40A are
described below. One key difference between system 40B and system
40A is that system 40B includes PPD 32B in lieu of PPD 32A. Unlike
PPD 32A, PPD 32B may perform pinna proximity detection without use
of adaptive gain control circuitry. When speaker SPKR is off ear,
the difference (as generated by combiner 164) between the energy of
the low-pass filtered error microphone signal and the output of
filter 156 may be small, and when speaker SPKR is on ear, such
difference may be significantly larger. Accordingly, pinna
proximity decision block 60B may utilize this difference to render
a pinna proximity decision.
[0094] Turning back to FIG. 13, system 40 is shown there using an
ambient noise estimator 82. FIG. 25 is a block diagram of an
example ambient noise estimator 82, in accordance with embodiments
of the present disclosure. To effectively estimate ambient noise,
it may be necessary to remove the sensed pilot signal PILOT', as
much as possible, from the bandpass-filtered error microphone
signal. Such removal may be performed by pilot tracker 56 depicted
in FIG. 13, or by an additional pilot tracker 166, as shown in FIG.
25, in order to predict sensed pilot signal PILOT'. Combiner 168
may subtract this predicted pilot signal from the bandpass-filtered
error microphone signal, resulting in a pilot-less
bandpass-filtered error microphone signal. An envelope detector 170
and linear-to-decibel converter 172 may further process the
pilot-less bandpass-filtered error microphone signal to generate an
estimate of ambient noise, which ambient noise estimator 82 may
communicate to pilot reference calculator 84.
[0095] As used herein, when two or more elements are referred to as
"coupled" to one another, such term indicates that such two or more
elements are in electronic communication or mechanical
communication, as applicable, whether connected indirectly or
directly, with or without intervening elements.
[0096] This disclosure encompasses all changes, substitutions,
variations, alterations, and modifications to the example
embodiments herein that a person having ordinary skill in the art
would comprehend. Similarly, where appropriate, the appended claims
encompass all changes, substitutions, variations, alterations, and
modifications to the example embodiments herein that a person
having ordinary skill in the art would comprehend. Moreover,
reference in the appended claims to an apparatus or system or a
component of an apparatus or system being adapted to, arranged to,
capable of, configured to, enabled to, operable to, or operative to
perform a particular function encompasses that apparatus, system,
or component, whether or not it or that particular function is
activated, turned on, or unlocked, as long as that apparatus,
system, or component is so adapted, arranged, capable, configured,
enabled, operable, or operative. Accordingly, modifications,
additions, or omissions may be made to the systems, apparatuses,
and methods described herein without departing from the scope of
the disclosure. For example, the components of the systems and
apparatuses may be integrated or separated. Moreover, the
operations of the systems and apparatuses disclosed herein may be
performed by more, fewer, or other components and the methods
described may include more, fewer, or other steps. Additionally,
steps may be performed in any suitable order. As used in this
document, "each" refers to each member of a set or each member of a
subset of a set.
[0097] Although exemplary embodiments are illustrated in the
figures and described below, the principles of the present
disclosure may be implemented using any number of techniques,
whether currently known or not. The present disclosure should in no
way be limited to the exemplary implementations and techniques
illustrated in the drawings and described above.
[0098] Unless otherwise specifically noted, articles depicted in
the drawings are not necessarily drawn to scale.
[0099] All examples and conditional language recited herein are
intended for pedagogical objects to aid the reader in understanding
the disclosure and the concepts contributed by the inventor to
furthering the art, and are construed as being without limitation
to such specifically recited examples and conditions. Although
embodiments of the present disclosure have been described in
detail, it should be understood that various changes,
substitutions, and alterations could be made hereto without
departing from the spirit and scope of the disclosure.
[0100] Although specific advantages have been enumerated above,
various embodiments may include some, none, or all of the
enumerated advantages. Additionally, other technical advantages may
become readily apparent to one of ordinary skill in the art after
review of the foregoing figures and description.
[0101] To aid the Patent Office and any readers of any patent
issued on this application in interpreting the claims appended
hereto, applicants wish to note that they do not intend any of the
appended claims or claim elements to invoke 35 U.S.C. .sctn. 112(f)
unless the words "means for" or "step for" are explicitly used in
the particular claim.
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