Title of Invention

APPARATUS AND METHOD FOR LEVEL-DEPENDENT COMPANDING FOR WIRELESS AUDIO NOISE REDUCTION

Abstract THE PR4ESENT INVENTION PROVIDES APPARATUS AND METHOD THAT MITIGATE THE NOISE INCURRED ON WIRELESS COMMUNIATYIONS PATH BETWEEN AN ENCODER AND A DECODER OF A WIRELESS AUDIO NOISE REDUCTION SYSTEM THAT UTILIZES FREQUENCY MODULATION (FM). THE ENCODER COMPRISES A VARIABLE COMPRESSIOR THAT INVLKES CIMPRESSION WHENEVER THE INPUT SIGNAL IS ABOVE A FIRST THREWHOLE LEVEL. THE DECODER COMRISES A VRIABLE EXPANDER THAT INVOKES EXPANSION WHENEVER THE RECEIVED SIGNAL FROM THE DECODER IS ABOVE A SECOND THRESHOLD.
Full Text APPARATUS AND METHOD FOR LEVEL-DEPENDENT COMPANDING
FOR WIRELESS AUDIO NOISE REDUCTION
FIELD OF THE INVENTION
The invention relates to wireless audio microphone systems.
BACKGROUND OF THE INVENTION
In order to provide audio communication between a talker and those listening to the talker,
audio electronic equipment is often utilized to facilitate the communication. The term "talker"
can connote a variety of input sources, including a person articulating language or a musical
band playing a song. Moreover, the talker may require an untethered connection to the audio
electronic equipment for greater mobility. A wireless connection between the acoustical
speaker and the electronics equipment can be provided by frequency (FM) radio techniques in
which the audio electronics equipment comprises a transmitter (which includes an encoder) and
a receiver (which includes an decoder). In such an arrangement, the transmitter processes the
audio signal as provided by the talker and modulates the signal so that the transformed signal
can be conveyed over the wireless path to a receiver. The receiver demodulates the received
signal, and the processed received signal is then presented to circuitry that may amplify the
processed received signal. The corresponding signal may be recorded by additional recording
circuitry or may be converted into an audio signal with an acoustical speaker arrangement.
The quality of the processed received signal, and consequently the associated audio signal, can
be degraded by any "noise" that is generated in the wireless path between the encoder and the
decoder. (The term "noise" is associated with a randomly varying signal superimposed on the
desired, undistorted signal). There are a number of sources of noise with respect to the wireless
path, including transmitter VCO (voltage controlled oscillator) phase noise, transmitter
synthesizer stability, the quality of the FM detector in the receiver, receiver RF band pass
filtering, and the receiver"s local oscillator. Moreover, with FM radio techniques the wireless
path is susceptible to FM noise generated when a weak radio signal as received by the receiver.
The FM noise results in the audio signal (as provided to the listener) having "breathing"
characteristics because of the similar sound characteristics of someone breathing. The
"breathing" effect is caused by the dynamic noise in conjunction with the type of companding.
Moreover, the degree of the "breathing" effect increases with the dynamic noise level. The
resulting effect can be noticeable to the listener and is perceived as a degradation of the audio
signal. Thus, a solution that ameliorates the "breathing" effect is an advancement in wireless
microphone technology.
BRIEF SUMMARY OF THE INVENTION
The present invention mitigates the "breathing effect" associated with a wireless
communications path between an encoder and a decoder of a wireless audio noise reduction
system. Otherwise, the listener perceives a sound that is characteristic of someone breathing.
The "breathing" effect is caused by the dynamic noise in conjunction with the type of
companding. Moreover, the degree of the "breathing" effect increases with dynamic noise
level.
The present invention provides apparatus and method to mitigate the corresponding breathing
effect. According to the present invention, the wireless audio noise reduction system comprises
an encoder and a decoder. The encoder comprises a variable compressor that invokes
compression whenever the input signal is above a first input threshold, a frequency modulation
(FM) modulator, and a matching network that interfaces the modulator to a first antenna that
transmits over the wireless communications path. The decoder receives a signal from the
encoder over the wireless communications path through a second antenna. The decoder
comprises a FM detector and a variable expander that invokes expanding operation above a
second input threshold.
An exemplary embodiment of the present invention is presented illustrating an architecture of
the encoder and decoder having a communications path such as a radio path or a cable.
Moreover, an electrical design of the encoder and decoder is presented with commercially
available components.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
Figure 1 shows a system architecture of a wireless audio noise reduction system in accordance
with the present invention;
Figure 2 shows a relationship of the gain function of a variable compressor;
Figure 3 shows a functional diagram of a variable compressor;
Figure 4 shows a functional diagram of a variable expander;
Figure 5 shows an electrical schematic diagram for implementing a variable compressor in
accordance with Figure 3; and
Figure .6 shows an electrical schematic diagram for implementing a variable expander in
accordance with Figure 4.
DETAILED DESCRIPTION OF THE INVENTION
Figure 1 shows a system architecture of wireless audio noise reduction system 100 in
accordance with the present invention. Input source 101 generates an acoustical signal that is
processed by input device 103 over transmission path 102. While Figure 1 depicts input source
101 as being a person, one skilled in the art appreciates that input source 101 can a person, a
musical instrument, a compact disc (CD), or any generator of a audio frequency band signal.
Input device 103 processes the signal produced by input source 101. Consequently, the
selection of input device 103 is dependent upon the selection of input source 101. For example,
if input source 101 is a person, a microphone is applicable as input device 103. If input source
101 is a CD, then the electronics associated with a CD player is applicable as input device 103.
Transmission path 102 is dependent upon the selection the selection of 101 and 103. Some
examples of transmission path 102 include air or a cable connecting 101 and 103.
HPF 105 is a high pass filter that reduces unwanted noise (e.g. wind noise while talking in a
car) that can be generated through transmission path 102. However, the need for including HPF
105 is dependent upon the characteristics of input source 101, transmission path 102, and input
device 103. Pre-emphasis circuit 107 enhances the gain of the higher frequency component of
the presented signal. It is well known in the art that the inclusion of a pre-emphasis circuit
increases the resulting signal to noise ratio (S/N) with frequency modulation techniques. The
resulting signal is the input signal to variable compressor 109.
Variable compressor 109 has a gain characteristic that is dependent upon the level of the input
signal. The gain characteristic is discussed in relation to Figure 2, while the operation of
variable compressor 109 is discussed in more detail with Figure 3. Variable compressor 109
invokes compression only if the input signal to 109 is above a first input threshold. If not (i.e.
the input signal is below the first input threshold), variable compressor 109 has a fixed gain
(typically between 35 and 50 dB). In other words, the compression characteristic of variable
compressor 109 is disabled.
The output of variable compressor 109 is processed by modulator 111. Modulator 111 utilizes
frequency modulation (FM) techniques. The resulting output of 111 is processed by matching
network 113. Matching network 113 matches the impedance of the encoder to the impedance
of antenna 115 and provides the desired signal level for transmission. Communications is
established between antenna 115 and antenna 117 over radio frequency (RF) path 116.
Alternative embodiments can utilize other types of transmission media other than a radio
frequency medium. Alternative examples include an infrared transmission medium and a
visible light medium.
The received signal that is received by antenna 117 of a decoder is processed by FM detector
119. FM detector 119 utilizes FM techniques to convert a FM signal into a baseband audio
signal. Amplifier 121 amplifies the output signal of FM detector 119 to an appropriate level.
Depending upon the characteristics of the received signal, amplifier 121 may not be required.
The output from amplifier 121 is processed by LPF 123, which is a low pass filter. The
response of LPF 123 in conjunction with the response of HPF 105 creates an effective band
pass filter that reduces ultra-sonic and sub-sonic information that may impede the operation of
variable expander 125. The output of LPF 123 is then processed by variable expander 125.
Variable expander 125 has an inverse gain characteristic of variable compressor 109 in order to
recover the input signal from input source 101. Variable expander 125 invokes expanding
operation if the input signal is above a second threshold level. Below the second threshold
level, expander 125 has a fixed gain to compensate for the corresponding fixed gain of variable
compressor 109. The operation of expander 125 is discussed in greater detail with Figure 4.
The output of variable expander 125 is then processed to de-emphasis circuit 127. De-emphasis
circuit has an essentially inverse gain function of pre-emphasis circuit 105. Thus, de-emphasis
circuit 127 has a higher gain for the lower-frequency component of an input signal. The
processed signal is presented to output device 129. Examples of output device 129 include a
mixing console, an acoustical speaker, and a recording device.
Even though Figure 1 shows a wireless system, the present invention is applicable to a non-
wireless system in which RF path 116 is replaced with a non-wireless transmission path such as
a cable, infrared transmission medium, or a visible Jight medium as can be appreciated by one
skilled in the art. The degree of "breathing" is dependent upon the amount of signal degradation
incurred with the non-wireless path. Moreover, as can be appreciated by one skilled in the art,
the present invention is applicable to audio communications system utilizing modulation
schemes other than frequency modulation.
Figure 2 shows a relationship of the gain function of variable compressor 109 that is shown in
Figure 1. Compressor input 201 (in dB) is mapped to compressor output 202 (in dB).
Whenever compressor input 201 is above .11 206, variable compressor 109 invokes
compression operation as reflected by curve 203. Graphical point 205 corresponds to II 206 in
which the associated compressor output is Ol 207. If compressor input 201 is below II 206,
then variable compressor 109 has a gain of essentially one as represented by curve 204.
In engineering the gain function of variable compressor 109, the designer must consider the
voltage rails associated with 109. The associated voltage levels of the processed signal are
restrained by the voltage levels of the power supply. Graphical point 205 is chosen in order to
satisfy the restraints as imposed by the voltage rails and the dynamic range requirement of
wireless audio noise reduction system 100. The gain function of variable expander 125 can be
derived from Figure 2 by replacing compressor input 201 with the expander output and by
replacing compressor output 202 with the expander input. By increasing the compression ratio
(as reflected in curve 203), the greater the value of compression input I1 206. The increased
value of 11 206 is desirable because the "breathing" effect (that is induced by the noise
generated on RF path 116) is mitigated. However, increasing the compression ratio requires
that the expansion ratio increase accordingly. However, with increased compression and
expansion ratios, the component tolerances of variable compressor 109 and variable expander
125 become more critical. If the compression and the expansion ratios become too large, the
practicality of wireless audio noise reduction system 100 is compromised.
Figure 3 shows a functional diagram of variable compressor 109. The input signal from pre-
emphasis circuit 107 is connected to input 300 of VCA (voltage controlled amplifier) 301.
VCA 301 is an amplifier whose gain varies with control voltage 302. The output of VCA 301 is
processed by amplifier 303 and LPF 305. LPF 305 is a low pass filter and functions as an
integrator to provide a desired time constant to mitigate undesired transients. LPF 305 is
optional to the design in accordance with the required filtering characteristics of the encoder"s
feedback. Output 316 of variable compressor 109 is processed by modulator 111 as well as
processed by a feedback loop circuit configuration comprising RMS detector 307, compressor
ratio and threshold circuit 309, and amplifier 311. RMS detector 307 processes the output from
LPF 305 so that the output of RMS detector 307 is representative of the root mean square
(RMS) value of output 316. Circuit ratio and threshold circuit 309 processes the output of RMS
detector 307 in order to invoke compressor operation above compressor input I1 206.
Moreover, circuit 309 insures that the signal levels of VCA 301 and 307 are compatible. Bias
offset circuit 313 is incorporated to insure that the bias level of VCA 301 is compatible with the
bias level of RMS detector 307. Trim circuit 315 provides symmetry in the associated
waveform in order to reduce distortion of the output of VCA 301.
Figure 4 shows a functional diagram of variable expander 125 as shown in Figure 1. Input 400
is connected to the output of LPF 123 in Figure 1. Output 412 is connected to the input of de-
emphasis circuit 127 in Figure 1. The functionality of VCA 401, expansion ratio and threshold
circuit 405, RMS detector 407, bias offset circuit 409, and trim circuit 411 correspond to the
functionality of VCA 301, compressor ratio and threshold circuit 309, RMS detector 307, bias
offset circuit 313, and trim circuit 315 respectively as shown in Figure 3. The design of
expansion ratio and threshold circuit 405 must account for the fact that gain function of VCA
401 is essentially the inverse function of the gain function of VCA 301.
Figure 5 shows an electrical schematic diagram for implementing variable compressor 109 in
accordance with Figure 3. In the illustrative implementation, integrated circuit 501 and
integrated circuit 510 are THAT2181 and THAT2252, respectively. Both integrated circuits are
manufactured by THAT Corporation. (Product specifications are available on the Internet at
www.thatcorp.com.) Alternatively, THAT4311 RMS detector may be substituted for
THAT2252 as integrated circuit 510. Input 300 is connected to pin 502 (in) and pin 503 (out) is
connected to operational amplifier 507. Operational amplifier 507 and resistor 508 correspond
to amplifier 303 in Figure 3. Pin 504 (EC-) is connected to the feedback loop comprising
amplifier 311, compressor ratio and threshold circuit 309, and RMS detector 307. Pin 505
(TRIM) is connected to 315. Pin 506 (EC+) is grounded.
The output of operational amplifier 507 corresponds to output 316, which is the output of
variable compressor 109. Moreover, output 316 is processed by RMS detector 307, which
comprises integrated circuit 510, resistor 509, resistor 515, and capacitor 516. Resistor 509 is
connected to pin 511 (in) of integrated circuit 510. Resistor 515, which is connected to pin 513
(It), and capacitor 516, which is connected to pin 514 (CT), allow for tuning the time constant
of integrated circuit 510. Pin 512 (out) is connected to the input of compressor ratio and
threshold circuit 309, which comprises resistors 518, 519, 521, and 523, operational amplifier
517, and diode 522. The compression threshold is determined by the corresponding DC offset
as adjusted by resistors 518, resistor 519, and voltage source 520 (-Vee)- The compression ratio
is determined by the gain of operational amplifier 517.
The output of compressor ratio and threshold circuit 309 is processed by amplifier 311, which
comprises operational amplifier 524, resistor 525, and resistor 526. The output of amplifier 311
is connected to pin 504 (EC-) in order to control the voltage gain of integrated circuit 501.
The distortion of the output of integrated circuit 501 is reduced by adjusting the voltage level
presented to pin 505 (TRIM) by trim circuit 315. Trim circuit 315 comprises resistor 528 and
529. The resistor configuration acts as a voltage divider that is coupled with voltage sources
520 (-VEE) and 527 (+VCc).
Figure 6 shows an electrical schematic diagram for implementing variable expander 125 in
accordance with Figure 4. in the illustrative implementation, integrated circuit 602 and
integrated circuit 609 are THAT2181 and THAT2252, respectively. Alternatively, THAT4311
RMS detector may be substituted for THAT2252 as integrated circuit 609. Input 400 is
connected to pin 603 (in) of integrated circuit 602 through resistor 601. Pin 604 (out) is
connected to output 402 of variable expander 125.
A control loop, comprising RMS detector 407, expansion ratio and threshold circuit 405, and
amplifier 403 is configured between input 400 and pin 605 (EC+) of integrated circuit 602. Pin
606 (TRIM) is connected to trim circuit 625, and pin 607 (EC-) is grounded.
RMS detector 407 comprises resistor 608, integrated circuit 609, resistor 614, and capacitor
615. Resistor 614, which is connected to pin 612 (It), and capacitor 615, which is connected to
pin 613 (Ct) allows for tuning the time constant of integrated circuit 609. Pin 611 (out) is
connected to the input of expansion ratio and threshold circuit 405, which comprises resistors
616, 618, 619, and 622, operational amplifier 617, and diode 521. The expander threshold is
determined by the corresponding DC offset as adjusted by resistors 618, resistor 619, and
voltage source 620 (-VEE). The expansion ratio is determined by the gain of operational
amplifier 620.
The output of expansion ratio and threshold circuit 405 is processed by amplifier 403, which
comprises operational amplifier 623, resistor 624, and resistor 626 through voltage source 625
(+Vcc)- The output of amplifier 403 is connected to pin 605 (EC+) in order to control the
voltage gain of integrated circuit 602.
The distortion of the output of integrated circuit 602 is reduced by adjusting the voltage level
presented to pin 606 (TRIM) by trim circuit 411. Trim circuit 411 comprises resistor 627 and
628. The resistor configuration acts as a voltage divider that is coupled with voltage sources
620 (-V,:,:) and 625 (+VCC).
While the invention has been described with respect to specific examples including presently
preferred modes of carrying out the invention a those skilled in the art will appreciate that there
are numerous variations and permutations of the above described systems and techniques that
fall within the sprit and sdcopr of the invention as set forth in the appended claims.
WE CLAIM :
wireless
1 An audio noise reduction system providing communication between an input source and
an output device (129), the system comprising :
an encoder comprising :
a variable compressor (109), receiving a signal derived from the input source through an
input device(103), the variable compressor invoking a compression operation above a
first input threshold, the compression operation being associated with a compression
ratio greater than one to one;
a modulator (111) connected to the variable compressor; and
a matching network (113) connected to the modulator, the matching network being
coupled to a first antenna(115);
a decoder communicating with the encoder, the decoder comprising :
a signal detector (119) having an input driven from a second antenna (117), the second
antenna being in wireless communication with the first antenna; and
a variable expander (125) connected to the signal detector, the variable expander
invoking expanding operation above a second input threshold, the expanding operation
having an expansion ratio greater than one to one - When the variable compressor of
the encoder comprises feedback means including compression ratio and threshold
function.
2. The system of claim 1, wherein the modulator (111) and the sjgnal detector (119) utilize
frequency modulation (FM) techniques.
3. The system of claim 1 or 2, further comprising :
a pre-emphasis circuit (107) connected between the variable compressor (109) and the
input source.
4. The system as claimed in any one of the preceding claims, further comprising
a high pass filter (105) connected between the variable compressor (109) and the input
source.
5. The system as claimed in any one of the preceding claims, wherein the compression
ratio is between three to one and eight to one.
6. The system as claimed in any one of the preceding claims, wherein the variable
compressor comprises :
a voltage controlled amplifier (VCA) (301) having an input driven by the input source
a root mean square (RMS) detector (307) connected to an output of the VCA; and
a compression ratio and threshold circuit (309) responsive to an output of the RMS
detector to control a gain function of the VCA.
7 The system of claim 6, wherein the variable compressor (109) further comprises:
a bias offset circuit (313) for reducing a bias difference of the RMS detector (307) and
the VCA (301).
8 The system as claimed in any one of the preceding claims, wherein the first antenna
(115) is integrated with the noise reduction system.
9 The system as claimed in any one of the preceding claims, wherein the input device
(103) is integrated with the audio noise reduction system.
10 The system as claimed in any one of the preceding claims, wherein the input device
(103) is selected from the group consisting of a microphone and a recording device.
11 The system as claimed in any one of the preceding claims, wherein the input device
(103) comprises at least one transducer.
12 The system as claimed in any one of the preceding claims, further comprising :
a de-emphasis circuit (127) connected between the variable expander (125 and the
output device (129).
13 The system of claim 1, further comprising :
a low pass filter (123) connected between the variable expander (125) and the signal
detector (119).
14 The system of claim 1, wherein the expansion ratio is between one to three and one to
eight.
15 The system as claimed in any one of the preceding claims, wherein the variable
expander (125) comprises :
a second VCA (401) having an input driven by the signal detector (119);
a second detector (407) connected to an output of the second VCA; and
an expansion ratio and threshold circuit (405) responsive to an output of the second
RMS detector to control gain characteristics of the second VCA.
16 The system of claim 15, wherein the variable expander (125) further comprises "
a bias offset circuit (409) for reducing a bias difference of the second RMS detector
(407) and the second VCA (401).
17 The system as claimed in any one of the preceding claims, wherein the second antenna
(117) is integrated with the noise reduction system.
18 The system as claimed in any one of the preceding claims, wherein said communication
between the input source and the output device (129) comprises wireless
communication.
19 An encoder for transmitting on a wireless path from an input source to a de coder, the
encoder being provided with an input signal from the input source, the encoder
comprising :
a variable compressor (109) receiving a signal from the input source through an input
device (103), the variable compressor comprising feedback means including
compression ratio and threshold function in order to invoke compression operation
above a first input threshold, the compression operation having a compression ratio
greater than one to one;
a modulator (111) connected to the variable compressor; and
a matching network (113) connected to the modulator, the matching network coupled to
a first antenna(115)
20 The encoder of claim 19, wherein the modulator utilizes frequency modulation (FM)
techniques.
21 The encoder of claim 19 or 20, further comprising :
a pre-emphasis circuit (107) connected between the variable compressor (109) and the
input source.
22 The encoder as claimed in any one of claims 19 to 21, further comprising.
a high pass filter (123) connected between the variable compressor (109) and the input
source.
23 The encoder as claimed in any one of claims 19 to 22, wherein the compression ratio is
between three to one and eight to one.
24 The encoder as claimed in any one of claims 19 to 23, wherein the variiable compressor
comprises :
a voltage controlled amplifier (VCA) having an input driven by the input source;
a root mean square (RMS) detector connected to an output of the VCA; and
a compression ratio and threshold circuit to an output of the RMS detector to control a
gain function of the VCA.
25 The encoder of claims 19 to 24, wherein the variable compressor (109) further
comprises :
a bias offset circuit (313) for reducing a bias difference of the RMS detector (307) and
the VCA (301).
26 The encoder as claimed in any one of claims 19 to 25, wherein the first antenna (115) is
integrated with the encoder.
27 The encoder as claimed in any one of claims 19 to 25, wherein the input device (103) is
integrated with the encoder.
28 The encoder as claimed in any one of claims 19 to 26, wherein the input device (103)
is selected from the group consisting of a microphone and a recording device.
29 The encoder as claimed in any one of claims 19 to 25, wherein the input device (103)
comprises at least one transducer.
30 A decoder for receiving a signal from an encoder on a wireless path, the decoder
provided a received signal from the encoder, the decoder comprising :
a signal detector (119) having an input driven by the received signal from a second
antenna (117) and
a variable expander connected to the signal detector, the variable expander invoking
expanding operation above a second input threshold, the expanding operation having an
expansion ratio greater than one to one the variable expander having an output driving
an output device (129).
31 The decoder of claim 30, wherein the signal detector utilizes frequency modulation (FM)
techniques.
32 The decoder of claim 30 or 31, further comprising :
a de-emphasis circuit connected between the variable expander and the output device.
33 The decoder as claimed in any one of claims 30 to 32, further comprising :
A low pass filter (123) connected between the variable expander (125) and the signal
detector (119).
34 The decoder as claimed in any one of claims 30 to 33, wherein the expansion ratio is
between one to three and one to eight.
35 The decoder as claimed in any one of claims 30 to 34, wherein the variable expander
(125) comprises :
a voltage controlled amplifier (VCA) (401) having an input driven by the signal
detector(119)
a root mean square (RMS) detector (407) connected to the VCA; and
an expansion ratio and threshold circuit (405) responsive to an output of the RMS
detector to control gain characteristics of the VCA.
"36 The decoder as claimed in claim 35, wherein the variable expander (125) further
comprises :
a bias offset circuit (409) for reducing a bias difference of the RMS detector (407) and
the VCA(401).
37 The decoder as claimed in any one of claims 30 to 36, wherein the second antenna
(117) is integrated with the decoder.
38 A method for encoding an input signal for transmission on a wireless path in order to
support noise reduction associated with the wireless path, the method comprising the
steps of:
variably compressing the input signal in which compression operation is invoked above
an input threshold in order to produce a processed signal;
frequency modulating the processed signal in order to produce a modulates signal;
transmitting the modulates signal through a first antenna
wherein the step of variably compressing is carried out through feedback means
including compression ratio and threshold function.
39 The method as claimed in claim 38, wherein the step of variably compressing the input
signal comprises :
adjusting a voltage control input of a voltage controlled amplifier (VCA)
measuring a root mean square (RMS) value of a signal that is derived from the output of
the VCA.
determining a compression ratio and a threshold for the compression ratio and threshold
function to control a gain function of the VCA
frequency modulating the processed signal in order to produce a modulates signal;
transmitting the modulated signal through a first antenna.
40 A method for decoding a received frequency modulated signal that is received on a
wireless path to support noise reduction on the wireless path, comprising the steps of:
detecting the received signal, the received signal being provided by a second antenna
(117) and
variably expanding, in accordance with a signal level, a detected signal as provided by
the step of detecting.
41 The method as claimed in claim 40, wherein the step of variably expanding the detected
signal comprises :
detecting the received signal provided by the second antenna (117);
adjusting a voltage control input of a voltage controlled amplifier (VCA) (401);
measuring a root mean square (RMSW) value of a signal that is derived from an output
of the VCA and
determining an expansion ratio and a threshold based on the measured RMS value to
control a gain function of the VCA.
The present invention provides apparatus and method that mitigate the noise incurred on a
wireless communications path between an encoder and a decoder of a wireless audio noise
reduction system that utilizes frequency modulation (FM). The encoder comprises a variable
compressor that invokes compression whenever the input signal is above a first threshold level.
The decoder comprises a variable expander that invokes expansion whenever the received
signal from the decoder is above a second threshold.

Documents:

450-kolnp-2004-granted-abstract.pdf

450-kolnp-2004-granted-claims.pdf

450-kolnp-2004-granted-correspondence.pdf

450-kolnp-2004-granted-description (complete).pdf

450-kolnp-2004-granted-drawings.pdf

450-kolnp-2004-granted-examination report.pdf

450-kolnp-2004-granted-form 1.pdf

450-kolnp-2004-granted-form 18.pdf

450-kolnp-2004-granted-form 2.pdf

450-kolnp-2004-granted-form 3.pdf

450-kolnp-2004-granted-form 5.pdf

450-kolnp-2004-granted-letter patent.pdf

450-kolnp-2004-granted-pa.pdf

450-kolnp-2004-granted-reply to examination report.pdf

450-kolnp-2004-granted-specification.pdf


Patent Number 213797
Indian Patent Application Number 00450/KOLNP/2004
PG Journal Number 03/2008
Publication Date 18-Jan-2008
Grant Date 16-Jan-2008
Date of Filing 05-Apr-2004
Name of Patentee SHURE INCORPORATED
Applicant Address 222 HARTREY AVENUE EVANSTON IL 60202 3696 USA.
Inventors:
# Inventor's Name Inventor's Address
1 CERRA DAVID 1709 PADDINGTON AVENUE NAPERVILLE USA.
PCT International Classification Number H04B1/64
PCT International Application Number PCT/US02/30439
PCT International Filing date 2002-09-25
PCT Conventions:
# PCT Application Number Date of Convention Priority Country
1 09/970, 400 2001-10-03 U.S.A.