U.S. patent application number 10/430863 was filed with the patent office on 2004-11-11 for associative noise attenuation.
Invention is credited to Cox, Stephen, Dutton, Drew J., MacDonald, James R..
Application Number | 20040222908 10/430863 |
Document ID | / |
Family ID | 33416333 |
Filed Date | 2004-11-11 |
United States Patent
Application |
20040222908 |
Kind Code |
A1 |
MacDonald, James R. ; et
al. |
November 11, 2004 |
ASSOCIATIVE NOISE ATTENUATION
Abstract
A system may include a memory configured to store an attenuation
waveform and control logic. The control logic is configured to
receive a synchronizing signal indicative of an operating
characteristic of a noise source. In response to a value of a
characteristic (e.g., frequency) of the synchronizing signal, the
control logic is configured to output the attenuation waveform from
the memory if the attenuation waveform is associated with that
value of the characteristic of the synchronizing signal. An
attenuating noise generated dependent on the attenuation waveform
attenuates a noise generated by the noise source.
Inventors: |
MacDonald, James R.; (Buda,
TX) ; Dutton, Drew J.; (Austin, TX) ; Cox,
Stephen; (Lakeway, TX) |
Correspondence
Address: |
Jeffrey C. Hood
Meyertons, Hood, Kivlin, Kowert & Goetzel PC
P.O. Box 398
Austin
TX
78767
US
|
Family ID: |
33416333 |
Appl. No.: |
10/430863 |
Filed: |
May 6, 2003 |
Current U.S.
Class: |
341/144 |
Current CPC
Class: |
G10K 2210/3033 20130101;
G11B 20/10009 20130101; G10K 11/1785 20180101; G10K 11/17883
20180101; G10K 2210/11 20130101 |
Class at
Publication: |
341/144 |
International
Class: |
H03M 001/66 |
Claims
1. A system, comprising: a memory configured to store a plurality
of attenuation waveforms; control logic configured to receive a
synchronizing signal indicative of an operating characteristic of a
noise source, wherein the control logic is configured to output
multiple attenuation waveforms from the memory if the multiple
attenuation waveforms are associated with a value of a
characteristic of the synchronizing signal; wherein attenuating
noise generated dependent on the multiple attenuation waveforms
attenuates a noise generated by the noise source.
2. The system of claim 1, further comprising a DAC (Digital to
Analog Converter) configured to generate an analog attenuation
signal from a digital representation of the plurality of
attenuation waveforms stored in the memory.
3. The system of claim 2, further comprising an actuator configured
to generate the attenuating noise in response to the analog
attenuation signal from the DAC.
4. The system of claim 1, wherein the memory is configured to store
digital representations of the plurality of attenuation waveforms,
wherein each of the digital representations is associated with a
respective value of the characteristic of the synchronizing
signal.
5. The system of claim 1, wherein the attenuation waveforms are
associated with ranges of values of the characteristic of the
synchronizing signal, and wherein the control logic is configured
to output the multiple attenuation waveforms from the memory if the
value of the operating characteristic is within the range of values
of the characteristic.
6. The system of claim 5, further comprising a processing device
configured to modify the multiple attenuation waveforms dependent
on the value of the characteristic prior to generation of the
attenuating noise dependent on the multiple attenuation
waveforms.
7. The system of claim 6, wherein the processing device is
configured to adjust amplitudes of the multiple attenuation
waveforms dependent on the value of the characteristic.
8. The system of claim 6, wherein the processing device is
configured to adjust a frequencies of the multiple attenuation
waveforms dependent on the value of the characteristic.
9. The system of claim 1, wherein the control logic is configured
to output the multiple attenuation waveforms from the memory if an
associated value of the characteristic associated with the multiple
attenuation waveforms is closer to the value of the characteristic
of the synchronizing signal than any other associated value of the
characteristic associated with other attenuation waveforms stored
in the memory; wherein the control logic is configured to perform
interpolation on the multiple attenuation waveforms dependent on a
relationship between the value of the characteristic of the
synchronizing signal and the associated value of the characteristic
associated with the multiple attenuation waveforms and to generate
a new attenuation waveform based on interpolation results.
10. The system of claim 1, wherein the characteristic of the
synchronizing signal is a frequency, wherein the synchronizing
signal is a tachometer signal indicative of revolutions per unit
time of a rotating component included in the noise source.
11. The system of claim 1, wherein the synchronizing signal is
indicative of an air density measured proximate to the noise
source.
12. The system of claim 1, wherein the synchronizing signal is
indicative of a system load of the noise source, wherein the noise
source includes a power supply.
13. The system of claim 1, wherein the synchronizing signal is a
non-acoustic signal.
14. The system of claim 1, wherein the memory and the control logic
are implemented on an integrated circuit, and wherein the
integrated circuit includes logic configured to perform additional
environmental control and monitoring functions.
15. A method, comprising: a memory storing a plurality of
attenuation waveforms; receiving a synchronizing signal indicative
of an operating characteristic of a noise source; if multiple of
the attenuation waveforms is associated with a value of a
characteristic of the synchronizing signal, outputting the multiple
attenuation waveforms from the memory in response to receiving the
synchronizing signal; an actuator generating an attenuating noise
dependent on the attenuation waveforms in response to said
outputting.
16. The method of claim 15, further comprising converting a digital
representation of the multiple attenuation waveforms stored in the
memory to an analog attenuation signal and providing the analog
attenuation signal to the actuator.
17. The method of claim 15, wherein said storing comprises the
memory storing digital representations of the plurality of
attenuation waveforms, wherein each of the digital representations
is associated with a respective value of the characteristic of the
synchronizing signal.
18. The method of claim 15, wherein the multiple attenuation
waveforms are associated with a range of values of the
characteristic of the synchronizing signal.
19. The method of claim 18, further comprising modifying the
multiple attenuation waveforms according to the value of the
characteristic of the synchronizing signal.
20. The method of claim 19, wherein said modifying comprises
adjusting amplitudes of the multiple attenuation waveforms
dependent on the value of the characteristic of the synchronizing
signal.
21. The method of claim 19, wherein said modifying comprises
adjusting frequencies of the multiple attenuation waveforms
dependent on the value of the characteristic of the synchronizing
signal.
22. The method of claim 15, further comprising: outputting the
multiple attenuation waveforms from the memory if an associated
value of the characteristic of the synchronizing signal associated
with the multiple attenuation waveforms is a closest one of a
plurality of associated values to the value of the characteristic
of the synchronizing signal, wherein each of the plurality of
associated values is associated with multiple respective
attenuation waveforms stored in the memory; and performing
interpolation on the multiple attenuation waveforms dependent on a
relationship between the value of the characteristic of the
synchronizing signal and the associated value of the operating
characteristic associated with the multiple attenuation
waveforms.
23. The method of claim 15, wherein the synchronizing signal is a
tachometer signal indicative of a number of revolutions per unit
time of a rotating part of the noise source, and wherein the
characteristic of the synchronizing signal is a frequency.
24. The method of claim 15, wherein the synchronizing signal is
indicative of an air density measured proximate to the noise
source.
25. The method of claim 15, wherein the synchronizing signal is
indicative of a system load of the noise source, wherein the noise
source includes a power supply.
26. The method of claim 15, wherein the synchronizing signal is
indicative of a non-acoustic operating characteristic of the noise
source.
27. The method of claim 15, further comprising: operating a
development system to generate the attenuation waveforms; and
writing the attenuation waveforms to the memory, wherein the memory
is included in an integrated circuit configured to perform said
receiving and said outputting.
28. The method of claim 27, wherein said operating the development
system comprises: operating the noise source over a range of values
of the operating characteristic indicated by the synchronizing
signal; and the development system generating multiple respective
attenuation waveforms for each of a plurality of values of the
operating characteristic indicated by the synchronizing signal;
wherein said writing comprises writing each of a plurality of
attenuation waveforms generated by the development system to the
memory included in the integrated circuit.
29. The method of claim 27, wherein said operating the development
system comprises a digital signal processor included in the
development system performing an algorithmic operation on a noise
signal indicative of noise generated by the noise source to
generate the digital representations of the attenuation
waveforms.
30. The method of claim 15, further comprising: receiving a
plurality of synchronizing signals, wherein each of the plurality
of synchronizing signals is indicative of an operating
characteristic of a respective noise source; selecting multiple
associated attenuation waveforms from the memory for each of the
plurality of synchronizing signals; combining a plurality of
associated attenuation waveforms selected by said selecting; the
actuator generating an attenuating noise dependent on a compound
attenuation waveform generated by said combining.
31. The system of claim 1, wherein the control logic updates one or
more of the attenuation waveforms stored in the memory based on the
synchronizing signals.
32. The system of claim 1, wherein the system and the noise source
are included in a computer system.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] This invention relates to the reduction of noise in consumer
electronics and, more particularly, to active noise
cancellation.
[0003] 2. Description of the Related Art
[0004] Active noise cancellation techniques are often used to
reduce noise. Typically, active noise cancellation involves
detecting the noise generated by a system and generating a
responsive cancellation wave that will reduce or even eliminate the
noise. Noise detection is typically performed using a microphone.
The analog signal detected by the microphone is converted into a
digital signal by an ADC (Analog to Digital Converter), which is
processed by a DSP (Digital Signal Processor) to generate a
compensating digital signal. The compensating digital signal is
provided to a DAC (Digital to Analog Converter), which converts the
digital signal into an analog signal for input to a speaker. While
often effective, active noise cancellation techniques require
expensive processing components and extensive hardware (e.g.,
microphones, ADC, DSP, DAC, speakers).
[0005] Consumer electronics contain numerous noise sources. For
example, computer systems include components such as fans, power
supplies, and disk drives, each of which may generate noise as it
operates. However, these components may be critical to system
functionality. Furthermore, given the size and/or cost of consumer
electronics, it may be impractical or uneconomical to include
typical active noise cancellation devices in consumer electronics.
If conventional noise cancellation techniques are unavailable,
designers of many consumer electronics are forced to balance
necessary functionality such as cooling against noise. This
trade-off may affect the performance, placement, size, life,
serviceability, and support cost of the product if less
functionality is provided in an attempt to reduce noise. For
example, product improvements may be limited by the lack of a
cooling fan in products in which a cooling fan is not currently an
option due to the unacceptability of its noise. Many products that
include fans are not optimal designs, have reduced features, or
cost significantly more in order to keep fan noise within customer
acceptable limits. Accordingly, new active noise cancellation
devices are desirable for use in consumer electronics.
SUMMARY
[0006] Various embodiments of a method and apparatus for providing
associative noise attenuation are disclosed. In one embodiment, a
system may include a memory configured to store an attenuation
waveform and control logic. The control logic is configured to
receive a synchronizing signal indicative of an operating
characteristic of a noise source. In response to a value of a
characteristic (e.g., frequency) of the synchronizing signal, the
control logic is configured to output the attenuation waveform from
the memory if the attenuation waveform is associated with that
value of the characteristic of the synchronizing signal. An
attenuating noise generated dependent on the attenuation waveform
attenuates a noise generated by the noise source.
[0007] In some embodiments, the system may also include a DAC
(Digital to Analog Converter) configured to generate an analog
attenuation signal from a digital representation of the attenuation
waveform stored in the memory. The system may also include an
actuator configured to generate the attenuating noise in response
to the analog attenuation signal from the DAC.
[0008] The memory may be configured to store digital
representations of a plurality of attenuation waveforms. Each of
the digital representations may be associated with a respective
value of the characteristic of the synchronizing signal.
[0009] The attenuation waveform may be associated with a range of
values of the characteristic of the synchronizing signal. The
control logic may be configured to output the attenuation waveform
from the memory if the value of the operating characteristic is
within the range of values of the characteristic. The control logic
may be configured to output the attenuation waveform from the
memory if an associated value of the characteristic associated with
the attenuation waveform is closer to the value of the
characteristic of the synchronizing signal than any other
associated values of the characteristic associated with other
attenuation waveforms stored in the memory. The control logic may
be configured to perform interpolation on the attenuation waveform
dependent on a relationship between the value of the characteristic
of the synchronizing signal and the associated value of the
characteristic associated with the attenuation waveform.
[0010] The system may include a processing device configured to
modify the attenuation waveform dependent on the value of the
characteristic of the synchronizing signal prior to generation of
the attenuating noise dependent on the attenuation waveform. For
example, the processing device may be configured to adjust an
amplitude of the attenuation waveform dependent on the value of the
characteristic. Similarly, the processing device may be configured
to adjust a frequency of the attenuation waveform dependent on the
value of the characteristic of the synchronizing signal.
[0011] In one embodiment, the characteristic of the synchronizing
signal may be the frequency of the synchronizing signal. The
synchronizing signal may be a tachometer signal indicative of
revolutions per unit time of a rotating component included in the
noise source. Alternatively, the synchronizing signal may be
indicative of an air density measured proximate to the noise
source. In other embodiments, the synchronizing signal may be
indicative of a system load of the noise source, wherein the noise
source includes a power supply. The synchronizing signal may be a
non-acoustic signal (e.g., the synchronizing signal may be
indicative of a non-acoustical operating characteristic of the
noise source).
[0012] An embodiment of a method may include: a memory storing an
attenuation waveform; receiving a synchronizing signal indicative
of an operating characteristic of a noise source; if the
attenuation waveform is associated with a value of a characteristic
of the synchronizing signal, outputting the attenuation waveform
from the memory in response to receiving the synchronizing signal;
and an actuator generating an attenuating noise dependent on the
attenuation waveform in response to said outputting.
BRIEF DESCRIPTION OF THE DRAWINGS
[0013] Other aspects of the invention will become apparent upon
reading the following detailed description and upon reference to
the accompanying drawings in which:
[0014] FIG. 1 shows a noise attenuation device 100, according to
one embodiment.
[0015] FIG. 2 illustrates an exemplary system that may include a
noise attenuation device, according to one embodiment.
[0016] FIG. 3 shows a development system that may be used to
generate the attenuation waveforms for storage in the noise
attenuation device, according to one embodiment.
[0017] FIG. 4 illustrates one embodiment of a method of performing
associative noise attenuation to reduce the noise generated by a
noise source.
[0018] While the invention is susceptible to various modifications
and alternative forms, specific embodiments thereof are shown by
way of example in the drawings and will herein be described in
detail. It should be understood, however, that the drawings and
description thereto are not intended to limit the invention to the
particular form disclosed, but, on the contrary, the invention is
to cover all modifications, equivalents, and alternatives falling
with the spirit and scope of the present invention as defined by
the appended claims.
DETAILED DESCRIPTION OF EMBODIMENTS
[0019] FIG. 1 shows a noise attenuation device 100, according to
one embodiment. Noise attenuation device 100 is configured to
perform associative noise attenuation for a noise source based on a
synchronizing signal generated by or associated with the operation
of that noise source. Based on one or more characteristics of the
synchronizing signal, noise attenuation device 100 selects a
pre-defined attenuation waveform associated with those
characteristics. Application of the selected attenuation waveform
to an actuator generates an attenuating noise that may attenuate
the noise generated by the noise source.
[0020] As shown in FIG. 1, a noise attenuation device may include:
one or more signal detectors 40 (here, four signal detectors
40A-40D are shown); one or more DACs (Digital to Analog Converters)
and/or amplifiers (Amps) 80 (here, four DAC/Amp units 80A-80B are
shown); control logic 20; attenuation waveform storage 30; output
control, sequencing, and clocking unit 50; and waveform processing
unit 60. The noise attenuation device 100 may be coupled to receive
one or more synchronizing signals via signal detectors 40 and,
based on those synchronizing signals, select one or more
pre-defined attenuation waveforms from attenuation waveform storage
30 to output to one or more actuators such as speakers
100A-100D.
[0021] The attenuation waveform storage 30 may be implemented using
various memory technology (e.g., flash memory, ROM (Read Only
Memory)). Storage 30 may store digital representations of several
pre-defined attenuation waveforms. Information indicative of the
synchronizing signal and synchronizing signal characteristic(s)
with which each pre-defined attenuation waveform is associated may
also be stored in storage 30. In some embodiments, the attenuation
waveform storage 30 may be updated at various times. For example, a
large set of pre-defined attenuation waveforms and/or information
associating pre-defined attenuation waveforms with synchronizing
signal characteristics may be stored externally to the noise
attenuation device 100 (e.g., in a less expensive mass storage
device). At any given time, a subset of these pre-defined
attenuation waveforms may be loaded into the attenuation waveform
storage 30. If any of various system characteristics change (e.g.,
if the type, age, or orientation of the noise source changes), new
pre-defined attenuation waveforms may be loaded from the external
storage into attenuation waveform storage 30. Noise attenuation
device 100 may include data inputs/outputs (not shown) to
facilitate reading and/or writing data in attenuation waveform
storage 30.
[0022] Control logic 20 may be configured to access information
stored in storage 30 (e.g., to access information indicating which
pre-defined attenuation waveform is associated with a particular
synchronizing signal characteristic) and to cause information from
storage 30 to be output to an actuator (e.g., via waveform
processing unit 60 and/or DAC/Amp units 80). Control logic 20 may
generate control signals to output unit 50 to control the output of
attenuation waveforms from storage 30 (e.g., by controlling the
rate at which data is clocked out of storage 30).
[0023] A synchronizing signal may be a signal that is generated by
a noise source during operation of that noise source. In some
embodiments, the synchronizing signal may not be an actual
measurement of the noise currently being generated by the noise
source. Instead, the synchronizing signal may be a non-acoustic
signal such as a tachometer signal indicative of a current
rotational speed (e.g., of a fan or disk drive), a signal
indicative of system load (e.g., if the noise source is a power
supply), a signal indicative of jitter (e.g., if the noise source
is a power supply), etc. In some embodiments, the synchronizing
signal may be a signal indicative of a condition, such as
vibration, air density, or pressure, measured at or near the noise
source during operation of the noise source. A synchronizing signal
for a given noise source may vary over the noise source's operating
range such that variations in a characteristic of the synchronizing
signal correlate to variations in the noise generated by the noise
source over its operating range.
[0024] Noise attenuation device 100 may receive several
synchronizing signals from a single noise source, a single
synchronizing signal from a single noise source, and/or single
synchronizing signals from each of several noise sources. In
response to receiving a synchronizing signal, a pre-defined of an
attenuation waveform associated with that synchronizing signal may
be output to one or more DAC/Amp units 80. In some embodiments,
noise attenuation device 100 may be programmable to select which
signal detector(s) 40 to associate with each DAC/Amp unit 80. For
example, noise attenuation device 100 may be programmed to receive
two synchronizing signals associated with a single noise source via
signal detectors 40A and 40B and to responsively output a
pre-defined attenuation waveform associated with the current values
of those synchronizing signals via DAC/Amp unit 80A. Noise
attenuation device 100 may be programmed to receive an additional
synchronizing signal associated with a different noise source via
signal detector 40C and to responsively output an associated
pre-defined attenuation waveform via DAC/Amp unit 80B. Noise
attenuation device 100 may also be programmed to receive a fourth
synchronizing signal associated with yet another noise source may
be received via signal detector 40D and to responsively output an
associated pre-defined attenuation waveform via DAC/Amp units 80C
and 80D. A noise attenuation device 100 may have many other
programmable or non-programmable configurations.
[0025] The control logic 20 may be configured to receive each
synchronizing signal detected by a signal detector 40 and to
determine whether a pre-defined attenuation waveform stored in
attenuation waveform storage 30 is associated with that
synchronizing signal. For example, various attenuation waveforms
stored in attenuation waveform storage 30 may be associated with
respective frequencies of the synchronizing signal. Dependent on
the current frequency of the synchronizing signal detected by a
signal detector 40, the control logic 20 may determine which of
several attenuation waveforms stored in attenuation waveform
storage is associated with the current frequency and cause the
attenuation waveform storage 30 to output the associated
attenuation waveform. For example, noise sources such as fans,
power supplies, and transformers may generate noise that is
periodic in nature. Synchronizing signals for such noise sources
may have frequencies that are often related to the frequency of the
noise. In such situations, the noise attenuation device 100 may
select the attenuation waveform that is associated with the current
frequency of the synchronizing signal.
[0026] Note that the control logic 20 selects a pre-defined
waveform to output based on whether that pre-defined waveform is
associated with the current synchronizing signal instead of
algorithmically calculating a waveform from the current
synchronizing signal. The pre-defined waveforms stored in
attenuation waveform storage 30, as well as information indicative
of the association between each pre-defined waveform and a
synchronizing signal, may be generated by a system such as the one
shown in FIG. 3 and programmed into the noise attenuation device
100 prior to operation of noise attenuation device 100. In other
words, the control logic 20 may perform little or no real-time
algorithmic processing of the synchronizing signal to obtain an
attenuation waveform. Instead, the algorithmic processing needed to
generate an attenuation waveform may be performed by a development
system like the one shown in FIG. 3. Accordingly, in some
embodiments, control logic 20 and waveform processing unit 60 may
be implemented using less complex hardware than is needed to
algorithmically generate attenuation waveforms from synchronizing
signals. In some such embodiments, this implementation may reduce
the cost, size, and/or power consumption of noise attenuation
device 100 relative to that of a device that algorithmically
generates attenuation waveforms.
[0027] In some embodiments, pre-defined digital representations of
attenuation waveforms may be stored for various points in a range
of synchronizing signal characteristics. For example, if a
synchronizing signal's frequency is capable of varying over a
range, pre-defined attenuation waveforms may be associated with
various frequency points within that range. When the frequency of
the synchronizing signal is not equal to one of the frequencies
with which a pre-defined waveform is associated, the control logic
20 may select the pre-defined waveform associated with the closest
frequency to the actual frequency of the synchronizing signal. The
control logic 20 may then provide control signals to waveform
processing unit 60 indicative of how the selected pre-defined
waveform should be adjusted to correspond with the actual
synchronizing signal frequency. For example, the waveform
processing unit 60 may perform frequency and/or amplitude
adjustment on the pre-defined waveform based on the relationship
between the actual synchronizing signal frequency and the
synchronizing signal frequency associated with that pre-defined
waveform. The waveform processing unit 60 may operate to
interpolate between pre-defined waveforms associated with discrete
points on the range of values of a synchronizing signal
characteristic to obtain a modified waveform appropriate for an
intermediate value of the synchronizing signal characteristic. For
example, if the attenuation waveform for different fan speeds is
identical other than the rate at which the waveform is sent to the
output device or the waveform's amplitude, then a reduced number of
attenuation waveforms may be stored in the memory 30. The
attenuation waveforms may then be adjusted or interpolated between
known points of operation and attenuation. This process of
adjustment and/or interpolation may be similar to how sampling
music synthesizers operate.
[0028] In some embodiments, interpolation or modification of a
selected attenuation waveform may be used to adjust for one or more
of various known or measurable factors, such as temperature, noise
source age, or barometric pressure. For example, as a fan ages, the
noise generated by that fan may change due to bearing wear or
dirt/dust accumulation. A noise attenuation device 100 configured
to attenuate noise generated by that fan may select a predefined
attenuation waveform based on the frequency of the tachometer
signal generated by that fan. The noise attenuation device 100 may
also track or receive an indication of the current age of the fan.
The noise attenuation device 100 may then modify the selected
attenuation waveform dependent on the current age of the fan.
[0029] In some embodiments, the noise attenuation device 100 may
combine and/or interpolate between several selected pre-defined
attenuation waveforms to form a compound attenuation waveform. The
noise attenuation device 100 may output such a combination waveform
via one or more DAC/Amp units 80. For example, the noise source may
include several fans. Each fan may generate a tachometer signal
that is input to a respective signal detector 40. The control logic
20 may select an associated pre-defined attenuation waveform in
memory 30 for each tachometer signal and combine the selected
attenuation waveforms (e.g., by adding, scaling, and/or performing
other operations on the selected attenuation waveforms) to form a
compound attenuation waveform, which may then be output to a
speaker or other actuator via a DAC/Amp unit 80.
[0030] Alternatively, in an embodiment configured to attenuate
noise generated by multiple noise sources, each pre-defined
attenuation waveform may be associated with a combination of
different synchronizing signals (as opposed to each attenuation
waveform being associated with a single synchronizing signal). For
example, a given attenuation waveform may be associated with a set
of tachometer frequencies, with each frequency in the set
corresponding to a different fan's tachometer signal (e.g., a
particular attenuation waveform may be associated with a set of
three fans in which one fan is running at 2200 RPM, another fan is
running at 1600 RPM, and yet another fan is running at 2800
RPM).
[0031] Output control, sequencing, and clocking unit 50 may select
the rate at which waveforms are output from attenuation waveform
storage 30. In one embodiment, output unit 50 may be used to adjust
the frequency of the waveform being output from attenuation
waveform storage 30. The output unit 50 may also allow multiple
attenuation waveforms to each be output to a different DAC/Amp unit
80 at substantially the same time by alternating between which of
the different waveforms is output in any given output cycle (e.g.,
dependent on the sample rate of the different waveforms).
[0032] FIG. 2 illustrates an exemplary system that may include a
noise attenuation device 100 that is configured to perform
associative noise attenuation. Here, a noise source 200 generates
noise while operating. Examples of different types of noise sources
200 include fans and other cooling devices, monitors (e.g., plasma
monitors, LCDs (Liquid Crystal Displays), CRTs (Cathode Ray
Tubes)), power supplies, and storage devices that include rotating
media such as hard drives, CD (Compact Disc) drives, and DVD
(Digital Versatile Disc) drives. These noise sources may be
included in products such as computer systems, televisions, and
projectors. For example, one or more fans may be included in a
projector in order to remove heat generated by a bulb used in the
projector. Similarly, noise sources may be included in consumer
electronics like DVD players, standalone or rack-mounted receivers,
and set-top boxes. Other noise sources include disk drives in
set-top-boxes (PVR/DVRs) and transformers that produce "hum" in
various consumer products.
[0033] In FIG. 2, a noise source 200 generates a synchronizing
signal. Different types of synchronizing signals may be generated
by different types of noise sources. For example, as mentioned
above, a fan noise source may generate a tachometer signal as its
synchronizing signal. Other noise sources with rotating parts such
as disk drives may also generate tachometer signals as their
synchronizing signals. As noted above, some noise sources may not
generate synchronizing signals. Instead, synchronizing signals may
be generated by sensors located around the noise source. Such
sensors may be configured to detect conditions such as air density,
vibration, and pressure and to provide synchronizing signals
indicative of the detected conditions to the noise attenuation
device 100.
[0034] The synchronizing signal is provided to the noise
attenuation device 100. Based on one or more characteristics (e.g.,
frequency and/or amplitude) of the synchronizing signal, the noise
attenuation device 100 selects a pre-defined attenuation waveform
and outputs the selected waveform to an actuator such as speaker
110. The noise attenuation device 100 may, in some embodiments,
modify the selected pre-defined waveform prior to outputting the
waveform to the speaker 110.
[0035] When the selected attenuation waveform is output to the
speaker 110, the speaker 110 generates noise. This noise may cancel
out all or part of the noise generated by noise source 200.
Placement of the speaker 110 may be selected relative to placement
of noise-generating component 200 and the expected placement of a
user (or users) such that the speaker's output will attenuate the
noise heard by the user (or users) due to the operation of noise
source 200.
[0036] Note that the attenuation waveform for a given noise source
may differ from one environment to another. The same type of noise
source may be associated with different attenuation waveforms
depending on the placement and/or orientation of the noise source
within an enclosure and/or relative to a user or the actuator that
outputs the attenuating noise. For example, a fan running at 2500
RPM in one enclosure (or in one position) may have a different
noise profile than the same fan in another enclosure (or position).
Accordingly, the attenuation waveforms generated by the development
system of FIG. 3 may vary depending on the overall system
configuration.
[0037] In some embodiments, the source of the synchronizing signal
(e.g., the noise source itself) and the speaker 110 may already be
part of the system that includes the noise source 200. For example,
the system may be a computer system that includes a fan noise
source. The fan may generate a tachometer signal that is used by
the computer system to detect whether the fan is operating
correctly. The computer system may include speakers that provide
multimedia functionality for the computer system. The noise
attenuation device 100 may be configured to receive the tachometer
signal and output attenuation waveforms to the pre-existing
speakers. Accordingly, the noise attenuation device 100 may be
incorporated in such a computer system without requiring additional
sensors or actuators to perform noise attenuation.
[0038] FIG. 3 shows a development system that may be used to
generate the attenuation waveforms for storage in the attenuation
waveform storage 30 of the noise attenuation device 100, according
to one embodiment. In this example, a noise source 200 is coupled
to provide a synchronizing signal to a computer system 300. A
microphone 120 or other sensor is configured to detect the noise
generated by the noise source 200 and to provide a signal
indicative of the detected noise to computer system 300.
[0039] The computer system 300 includes a processor 320 and a
memory 310. The processor 320 may be a digital signal processor
(DSP). The processor 320 may perform an algorithmic operation on
the noise signal detected by the microphone 120 to generate an
attenuation waveform. The processor 320 may store the attenuation
waveform generated by the algorithmic operation along with an
indication of one or more characteristics of the synchronizing
waveform at the time the noise signal was detected in memory
310.
[0040] The computer system 300 may output the generated attenuation
waveform to an actuator such as speaker 110. By measuring the noise
detected by the microphone 120 while the attenuation waveform is
being output to the speaker 110, the computer system 300 may
determine the effectiveness of the noise attenuation provided by
using the generated attenuation waveform. Based on this
determination, the processor 320 may modify the generated
attenuation waveform or generate a new attenuation waveform to
improve the attenuation of the noise generated by noise source 200.
The updated or new attenuation waveform may be stored with the
current characteristic(s) of the synchronizing waveform in memory
310.
[0041] The computer system 300 may generate attenuation waveforms
and store attenuation waveform/synchronizing signal characteristic
pairs in memory 310 for each of several different synchronizing
signal characteristics over the operating range of the noise source
200. For example, if the noise source 200 is or includes a fan, the
fan may be operated at several different speeds. If the
synchronizing signal for the fan is a tachometer signal, the
tachometer signal may have a different frequency at each of the
different speeds. For each of several different tachometer signal
frequencies, the computer system 300 may generate a new attenuation
waveform and store the generated attenuation waveform and its
association with that particular tachometer signal frequency in
memory 310.
[0042] The computer system 300 may continue to generate attenuation
waveforms until the computer system 300 has generated satisfactory
waveforms for each desired point within the noise source's
operating range. The final attenuation waveforms and their
respective associations with different synchronizing signal
characteristics may be used to program the noise attenuation device
100. For example, the synchronizing signal
characteristic/attenuation waveform pairs may be stored in
attenuation waveform memory 30 of noise attenuation device 100.
[0043] FIG. 4 illustrates one embodiment of a method of performing
associative noise attenuation to reduce the noise generated by a
noise source. At 401, a synchronizing signal is received. The
synchronizing signal may be generated by the noise source in some
embodiments. The synchronizing signal may not be an acoustic
signal. For example, the synchronizing signal may be a tachometer
signal indicative of how fast a rotating part within the noise
source is rotating.
[0044] The synchronizing signal may have various characteristics,
such as frequency and amplitude. Each value (or range of values) of
one or more of these characteristics may be associated with a
pre-defined attenuation waveform. Based on the current value of the
characteristic(s) of the synchronizing signal, the associated
pre-defined attenuation waveform may be selected, as shown at
403.
[0045] In some embodiments, the attenuation waveform selected at
403 may be additionally processed before being provided to an
actuator, as shown at 405. For example, the selected attenuation
waveform may be frequency- or amplitude-adjusted based on one or
more characteristics of the synchronizing signal. Note that
function 405 may not be implemented in some embodiments,
however.
[0046] At 407, the selected attenuation waveform may be output to
an actuator such as a speaker. In response, the speaker may output
a noise that attenuates all or part of the noise generated by a
noise source with which the synchronizing signal received at 401 is
associated.
[0047] Note that at least a portion of the system shown in FIG. 1
may be implemented as an integrated circuit. Additionally, the
system shown in FIG. 1 may be incorporated into a larger system
that implements additional functionality. For example, in one
embodiment, the noise attenuation device 100 may be incorporated in
an existing EMC (Environmental Monitoring and Control) integrated
circuit.
[0048] Numerous variations and modifications will become apparent
to those skilled in the art once the above disclosure is fully
appreciated. It is intended that the following claims be
interpreted to embrace all such variations and modifications.
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