U.S. patent number 3,730,995 [Application Number 05/199,228] was granted by the patent office on 1973-05-01 for voice switched microphone control system.
This patent grant is currently assigned to Bell Telephone Laboratories, Incorporated. Invention is credited to Max Vernon Mathews.
United States Patent |
3,730,995 |
Mathews |
May 1, 1973 |
VOICE SWITCHED MICROPHONE CONTROL SYSTEM
Abstract
Voice activated control apparatus selectively connects one of a
plurality of microphones to an audio line and inhibits all other
microphones from capturing the line while the initial connection is
maintained. Each microphone is connected to an associated speech
detector and relay. In response to voice signals from a microphone,
the associated speech detector activates a relay which connects the
microphone to the line and generates a signal which inhibits the
other relays. Other users cannot interrupt the present speaker
because their relays remain inhibited as long as the speaker
continues. The same circuitry can accommodate any number of
microphones.
Inventors: |
Mathews; Max Vernon (New
Providence, NJ) |
Assignee: |
Bell Telephone Laboratories,
Incorporated (Murray Hill, NJ)
|
Family
ID: |
22736711 |
Appl.
No.: |
05/199,228 |
Filed: |
November 16, 1971 |
Current U.S.
Class: |
381/110;
704/E11.003 |
Current CPC
Class: |
G10L
25/78 (20130101) |
Current International
Class: |
G10L
11/00 (20060101); G10L 11/02 (20060101); G10l
001/04 () |
Field of
Search: |
;179/1CN,1VC,1HF,30,31,32,33 ;340/148,415,295,217 |
References Cited
[Referenced By]
U.S. Patent Documents
Other References
IBM Technical Disclosure Bulletin, Vol. 5, No. 11, April 1963, p.
79..
|
Primary Examiner: Claffy; Kathleen H.
Assistant Examiner: Olms; Douglas W.
Claims
What is claimed is:
1. A voice activated switching system for selectively connecting
one of a plurality of speech circuits to an output line and for
inhibiting the connection of all others of said speech circuits to
the line while the connection is maintained, which comprises:
a plurality of circuits for conveying speech,
a speech detector associated with each of said circuits for
generating a first signal coincident with speech signals applied
from that one of said speech circuits associated therewith,
an output line for conveying speech,
generating means for developing control signals,
switching means associated with each of said speech circuits and
its associated speech detector wherein each of said switching means
is deactivated by control signals and activated, in the absence of
said control signals, by said first signal generated by said
associated speech detector,
a control line connected to each of said switching means for
conveying control signals, and
switching contacts associated with each of said switching means
which when activated by said associated switching means connect
with associated speech circuit to said output line, disconnect said
associated switching means from said control line, and connect said
generating means to said control line.
Description
FIELD OF THE INVENTION
This invention relates to audio systems and, more specifically, to
systems for selectively connecting speech circuits to an audio line
in response to voice signals.
BACKGROUND OF THE INVENTION
In classrooms and auditoriums it has been customary to employ a
number of microphones in various locations within the room in order
that questions and comments by members of the audience may be heard
by others. The voice signals input into the microphones are
amplified and conveyed through loud speakers to the immediate
audience. If desired, the signals may also be transmitted to select
individuals via the telephone system, or to the public at large via
the broadcast media.
In such systems, difficulties arise when more than one user speaks
at the same time. Since all the microphones have equal access to a
central amplifying system, more than one set of voice signals is
concurrently amplified. Thus, an unintelligible combination of
speech is often transmitted to the audience. To avoid this
difficulty, human monitors are often employed to insure that only
one member of the audience is afforded access to a microphone at a
given time.
In order to overcome this problem, other systems employ
sophisticated speech detectors and complicated logical gating
arrangements to first determine which micro-phones are being used
and then to selectively connect one of these microphones to the
audio line. The selection is made by comparing signal strengths in
a centralized logic arrangement. The microphone used by the loudest
talker is connected to the line. Such systems are a great
improvement over those previously used since the speech of a single
user rather than from a multitude of users is conveyed to the
audience at a given time. However, since the loudest user gains
access to the audio line even if he interrupts one who is presently
talking, there is a great tendency for an anxious questioner to
interrupt the present user before he has concluded his discussion.
It is conceivable that a shouting match might develop when several
users, each wishing to be heard, speak successively louder in order
to capture the system's output.
Furthermore, since these systems are fairly complex, they are not
as flexible as prior systems since the central logic has to be
altered when a microphone is added to the system. Such alterations
require adding additional logic.
It is an object of this invention to selectively connect a
microphone to an audio line in response to voice signals and to
inhibit all other microphones from capturing the line as long as
the present speaker continues to speak.
It is a further object of this invention to connect or disconnect
any number of microphones from the system without either
interrupting system operation or requiring an alteration in system
logic.
SUMMARY OF THE INVENTION
The present invention stems from the recognition that by
decentralizing the decision making apparatus the versatility of
simpler microphone systems is retained while gaining an additional
inhibiting feature. Each microphone is connected to an associated
device which autonomously determines whether to connect that
microphone to the audio line given the information specifying
whether one of the other microphones is presently connected to the
line.
In accordance with one illustrative embodiment of the principles of
this invention, control apparatus selectively connects one of a
plurality of microphones to an audio line and inhibits all other
microphones from capturing the line while the initial connection is
maintained. Each microphone is connected to an associated speech
detector and relay. The microphone, speech detector and relay form
a self-contained module which may be plugged in or out of a single
cable without interfering with the operation of the other
modules.
When a user speaks into his microphone, the associated speech
detector detects the speech and activates the associated relay. The
relay connects the microphone to the audio line and grounds a
control line which inhibits the other relays. As long as the user
continues talking, his microphone remains connected to the audio
line and the other relays are deactivated by the grounded control
line. When the user completes his talk, his microphone is
disconnected from the audio line and the ground is removed from the
control line. Other users are then able to capture the audio line.
The speech detectors have a built-in time delay to bridge the
pauses between spoken words.
GENERAL DESCRIPTION
The single FIGURE is a schematic block diagram of an illustrative
microphone control system embodying the principles of this
invention. When spoken into, each of the microphones M.sub.1, . . .
M.sub.i bids for access to audio line 10. When a microphone is
subsequently connected to the audio line, the voice signals input
into the microphone are conveyed to amplifier 11 which amplifies
the signals for transmission and subsequent conversion to audible
speech. The other microphones are inhibited from capturing the
audio line while the initial connection is maintained.
Each of microphones M is connected to an associated speech detector
SD.sub.1, . . . SD.sub.i. Each of speech detectors SD comprises
filters for distinguishing voice frequencies and a logical
arrangement for outputting a predetermined positive voltage over
its respective output lead A.sub.1, . . . A.sub.i when it detects
speech. When no speech is detected, each of the speech detectors
grounds its respective output lead A. To allow for pauses which
occur in normal speech, each of the speech detectors has sufficient
hysteresis so that the output signals remain at the positive
voltage during gap between words.
Bus 1 which houses control line 14, audio line 10, power line 12,
and ground line 15 may be a single cable with access ports at
conveniently spaced distances. Each of the microphone units
MU.sub.1, . . . MU.sub.i preferably is a self-contained module
which may be easily plugged in or out of bus 1. The bus may be
positioned along an arbitrary path in a room and the microphone
units plugged in where they are needed.
It should be noted that the Figure employs a type of notation
referred to as "detached contact" in which an "X" represents a
normally open contact of a relay, and a bar, shown intersecting a
conductor at right angles, represents a normally closed contact of
a relay; "normally" referring to the unoperated condition of the
relay.
SPECIFIC DESCRIPTION
The operation of the control system shown in the Figure is best
understood by considering three illustrative cases. In the first
case, voice signals are input into one of the microphones at a time
when all of the microphones are disconnected from the audio line.
In the second situation, a microphone user attempts to access the
line while another microphone remains connected to the line.
Finally, a microphone connected to the line is disconnected when
voice signals are no longer input into the microphone.
Turning now to the first situation, all of the microphones M are
disconnected from audio line 10. Since speech is not detected by
any of speech detectors SD, output leads A are all at ground
potential. Current flows from power source 13 over power line 12
through each of resistors R.sub.1, . . . R.sub.i and through each
of diodes D.sub.1, . . . D.sub.i to ground (via output leads A).
Diodes D are forward biased and each of the points X.sub.1, . . .
X.sub.i is at a voltage equal to the voltage drop across its
respective diode D (normally about 0.7 volts). Diodes DA.sub.1, . .
. DA.sub.i are substantially not in conduction and control line 14
floats.
The user of microphone M.sub.1 wishing to capture the audio line
speaks into his microphone. Speech detector SD.sub.1 in response to
the voice signals places a positive potential on the previously
grounded lead A.sub.1. The positive potential reverse biases diodes
D.sub.1. The current from resistor R.sub.1 flows through relay
winding W.sub.1 activating the relay. Relay contact W.sub.1 -B
closes connecting microphone M.sub.1 to audio line 10 via line
L.sub.1. Contacts W.sub.1 -A also operate both disconnecting diode
DA.sub.1 from control line 14 and grounding control line 14. As
long as speech detector SD.sub.1 detects speech from microphone
M.sub.1, a positive potential is conveyed over lead A.sub.1 and
relay W.sub.1 remains operative.
While control line 14 remains grounded by relay W.sub.1, the other
relays W.sub.2, . . . W.sub.i are inhibited from operating. Current
flows through resistors R.sub.2, . . . R.sub.i through forward
biased diodes DA.sub.2, . . . DA.sub.i to grounded control line 14.
Thus points X.sub.2, . . . X.sub.i are slightly above ground
potential and insufficient current flows through relay windings
W.sub.2, . . . W.sub.1 to activate these relays.
Now consider the second situation which illustrates the inhibiting
feature of the control system. The user of microphone M.sub.2
speaks into his microphone and attempts to interrupt the user of
microphone M.sub.1 who has previously captured audio line 10.
Speech detector SD.sub.2 in response to the voice signals from
microphone M.sub.2 places a positive potential on lead A.sub.2
reverse biasing diodes D.sub.2. Relay W.sub.2 does not operate
because point X.sub.2 still remains just above ground potential
because diode DA.sub.2 is forward biased through relay contact
W.sub.2 -A to grounded control line 14. Control line 14 remains
grounded by the continuing activation of relay W.sub.1 in response
to speech signals from microphone M.sub.1. Thus, as long as control
line 14 remains grounded in response to voice signals from a
microphone, all the other microphones are inhibited from capturing
audio line 10 since their associated relays are inhibited from
operating.
In the third case, the user of microphone M.sub.1 completes talking
and thereby relinquishes his grasp over audio line 10. Speech
detector SD.sub.1, when it no longer detects voice signals from
microphone M.sub.1, grounds lead A.sub.1. Diode D.sub.1 goes into
forward conduction, the voltage at point X.sub.1 drops, and relay
W.sub.1 deactivates due to insufficient current through relay
winding W.sub.1. Relay contacts W.sub.1 -A and W.sub.1 -B return to
their normal positions. Relay contact W.sub.1 -B opens
disconnecting microphone M.sub.1 from audio line 10. Control line
14 floats when contact W.sub.1 -A disconnects the ground from the
line. Now each of the users of microphone M is afforded an equal
opportunity to access audio line 10.
* * * * *