Abstract: An audio processor consisting of a "single-ended" dynamic noise reduction system cascaded and cross-coupled with a program-adaptive dynamic equalizer. The audio at the output has a consistent subjective spectral texture even if the spectral texture of the input audio varies widely. Further, although the system often adds high frquency energy to the audio, it does not increase the perceived noise level and is free from audible noise modulation.

Abstract: A receiver for receiving a transmitted signal comprising first and second bandwidth limited component signals modulating a single high frequency carrier in phase quadrature with the first component signal as originally transmitted including an identification signal has a source of a reference signal subject to phase error. Circuitry combines the received transmitted component signals with the reference signal to provide first and second demodulated signals characteristic of the first and second component signals respectively. A detector responds to the first and second demodulated signals to provide first and second detected components of the identification signal. Feedback circuitry responds to the detected components of the identification signal by providing a correction signal that is applied to the source of reference signal to reduce the phase error.

Abstract: A method and apparatus for signal companding is disclosed that incorporates a log-offset companding technique to provide both a high bandwidth over the dynamic range of the signal being processed as well as temperature stability. In addition, the incorporation of log-offset companding technique provides the capability of generating a family of transfer curves. The ability to provide a family of transfer curves is particularly useful, for example, in telecine machines adapted to scan more that one type of film.

Abstract: A system is provided for use with an electrical musical instrument for conditioning electrical signals generated by the instrument. The system includes an amplifier circuit having an input for responding to the signals and an output to provide a conditioned output signal. At least one compressor is operatively connected to the input for responding to the amplitude of the signals to provide a compressed signal to the amplifier circuit that is variable as a nonlinear function of the amplitude. Also provided are a pair of bandpass filters in parallel for frequency preemphasis of the compressed signal. Also provided is time modulation circuitry for permitted certain musical sound effects.

Abstract: A stereo FM radio transmission system with FMX transmission and reception capability includes a transmitter that transmits a pilot-coherent FMX-tone indicator signal at a frequency of an exact integer submultiple of the pilot frequency. The system also includes a receiver for dividing the frequency of the received pilot signal by various submultiples, nearly equal to the exact submultiple, toward quickly finding a match in phase of the received tone and the received pilot and finally dividing the pilot by the exact submultiple to establish an operational lock mode of the receiver tone detector to keep-on an FMX-indicator lamp, to change the receiver decoder to an FMX-reception operating mode and to stand by to quickly recapture the pilot and FMX-tone in the event of multipath or other interfering signals.

Abstract: In an amplitude expanding/compressing circuit for expanding, compressing, or expanding and compressing an amplitude of an input signal, the following are provided:a control signal generator which receives an input signal and generates a control signal from said input signal;a signal multiplier for multiplying the control signal and the input signal to generate a multiplied output;a first subtracter for subtracting the input signal from the multiplied output to generate a first subtracter output signal;a signal processor which receives the first subtracter output signal and generates a processed output from said first subtracter output; anda second subtracter for subtracting the processed output from the multiplied output to obtain an amplitude expanded, amplitude compressed, or amplitude expanded and compressed output signal.

Abstract: An audio compression circuit for limiting an audio television signal in a linear fashion at a pre-established maximum level is disclosed. The circuit includes a series resistance circuit for establishing a predetermined resistance on an amplifier to establish a supply voltage through a detection and level adjustment circuit. The detection and level adjustment circuit increases the supply voltage to a relatively higher reference voltage, which is shifted through a level adjustment circuit to a control voltage, which control voltage is greater than a threshold voltage of a field effect transistor. The field effect transistor is a significant aspect of a shunt circuit connected in parallel to the detection and level adjustment circuit. The shunt circuit acts in response to the control voltage to vary the resistance across the drain and source of the field effect transistor to prevent the outlet voltage to a loudspeaker from exceeding a predetermined level established by the level adjustment circuit.

Abstract: A line noise signal measurement system is provided with detecting circuitry for providing a sensed analog signal. Compression circuitry is coupled to the detecting circuitry for providing an amplitude compressed signal responsive to the applied sensed signal. The compression circuitry has a stepwise substantially linear transfer function responsive to a variable magnitude of the applied sensed signal. Signal processing circuitry is coupled to the compression circuitry for sequentially generating a digital signal representative of the sensed analog signal. Digital processing circuitry sequentially identifies a maximum peak signal for a predetermined time interval and provides linearity correction for the identified maximum peak signals and generates a display of the corrected peak signals.

Abstract: In circuits for generating rapidly changing, yet smooth and controlled, control signals in response to transient signals for use in audio compressors and expanders, a steady-state portion of the control circuit includes first and second smoothing stages (alternatively, a single stage may be employed) and an overshoot suppression portion of the control circuit rapidly charges the capacitor in the steady-state smoothing stage from which the control voltage is derived. A first additional overshoot suppression circuit provides further charging of the capacitor in response to low frequency signal components. Modulation control signals, which make the compressor or expander less susceptible to control by stop-band signal components, are combined in opposition to the signals in the steady-state and overshoot suppression portions of the control circuit.

Abstract: An FMX stereophonic receiver for receiving an FMX stereophonic broadcast signal, which includes a stereo sum signal, a stereo difference signal and a compressed stereo difference signal, is disclosed. When multipath interference takes place, noise signal will be produced, which adversely affects on a level control of an added signal of the stereo difference signal and the compressed stereo difference signal. The disclosed receiver includes a detector for detecting the multipath noise signal contained in the FMX stereophonic broadcast signal. When the multipath noise signal is detected, FMX receiving mode is automatically changed to FM receiving mode by a selecting means, so as to reduce the affect of the noise signal.

Abstract: The specification discloses an audio signal level control system including a center-tapped photocell incorporated into an attenuator bridge. The cell elements are monitored while processing the audio signal, and a control circuit regulates the light-emitting device in the cell in response to the monitored bridge values. Preferably, log compression and filtering are performed within the control means. Also preferably, a tracking subtraction principle is used in both the audio and control paths to expand the control dynamic range.

Abstract: A noise reduction system compresses an input signal at a constant ratio in response to a control signal derived from the compressed signal. Added to the derived control signal is a counterfeit control signal which causes the compressor to mistrack when the compressed signal falls below a preselected threshold level. Thus, low level compressor output signals are increasingly deemphasized. A constant counterfeit control signal produces a logarithmic decrease in compressor output signal levels below the threshold point. The resulting compressed signal is used to enhance system noise reduction. The input signal is fed to a filter having a variable bandwidth controlled by a signal derived from the compressed signal and responsive to compressed signal frequency and amplitude so that the filter is desensitized to input signal amplitude changes. A multistage filter control signal arrangement may be employed to provide variable cutoffs in more than one bandwidth.

Abstract: A voice control circuit controls the volume range of the voice signals in a communication terminal, such as a video telephone having a hands-free facility. In a hands-free facility, the signal-to-noise ratio is lower than in telephones with handset. To avoid audible feedback, hands-free facility conventionally includes a volume control circuit which decreases or increases the gain in the receive path as the gain in the set path increases or decreases. The problem to be solved is to utilize the maximum possible loop gain without reducing the gain in the receive path. The idea is to place behind the microphone (50) a controllable compandor (52) in which the signal voltages from the microphone (50) are A. compressed if they lie above a predetermined level, B. expanded if they lie below the predetermined level, and C. imparted maximum gain if they have the predetermined level.

Abstract: A programmable low voltage compressor circuit suitable for use with hearing aids is described. The compressor has a continuously variable compression ratio wherein the gain of the compressor may be programmably controlled over a wide range and the compressor may be powered from a power source as low as 1.1 volt. The compressor employs a variolosser wherein the gain is controlled by the ratio of the currents flowing out of first and second control terminals. A control circuit coupled to the variolosser controls the magnitude of the currents flowing out of the two control terminals. The control circuit includes a peak detector which generates a signal related to the peak positive envelope of the signal input to the compressor. A voltage to current converter is coupled to the peak detector for increasing the magnitude of the current flowing out of one of the control terminals of the variolosser as the voltage output of the peak detector increases.

Abstract: A programmable low voltage multi-band compression system suitable for use with hearing aids is described. Received audio signals are processed by a band split filter which separates the received audio signal into a plurality of frequency bands. A plurality of compressors coupled to the band split filter compresses each of the respective frequency bands. The output of the compressor are then summed to generate a composite audio signal. The compression ratio of each of the compressors is set, in response to a set of control signals, to a preselected independent value. The average gain of each of the compressors is set to a preselected level independently of the other compressors. In addition, the compression ratio of each compressor may vary with input signal level. Another set of control signals is employed for setting the gain of the compressor to provide a volume control function.

Abstract: To improve the fidelity of reproduction of automobile radios during conditions of extraneous in the passenger compartment, noise signals are derived, for example from a microphone installed in the engine compartment of the vehicle. The audio program signals are conducted through a multichannel equalizer; the program audio signals and the noise signals are separated into a plurality of frequency bands, for example three bands, the envelope of which are demodulated and the derived demodulation signals are instantaneously compared to then control the transfer characteristics of the respective bands of the equalizer in accordance with the derived comparison between the respective bands of the noise and program signals. Preferably, amplitude, change of transfer amplitude and rate of change is controlled by weighting the comparison signals and the rate of change thereof in relation to the frequency bands and the extent of change of the signals.

Abstract: A sound mixing control system applicable to recording, broadcast and sound reinforcement systems. The gain provided for each input channel through the system is monitored, and whenever the sum of all the gains exceeds a threshold the overall gain is reduced to limit the sum of the gains to the threshold. Simultaneously the output level of the mixer is measured, and whenever the level would otherwise exceed a threshold the gains of the input channels are reduced in proportion to their individual levels to limit the output level to the desired maximum. Signals may be divided into multiple frequency bands, processed in parallel and recombined.

Abstract: In a signal processing system used for recording and reproducing acoustic signals, a compressor comprises a first detector for detecting an output signal from an amplifier by a first time constant, a second detector for detecting the output signal from the amplifier by a second time constant which is shorter than the first time constant, a threshold means for detecting a signal from the second detector to output a signal component exceeding a threshold level, and a combining means for combining signals from both the first detector and the threshold to thereby generate an output to the amplifier.

Abstract: A teleconference system comprises a plurality of microphones and a plurality of expanders connected respectively thereto for expanding the outputs of the microphones. A summing ammplifier produces a sum of the output signals of the expanders and feeds a compressor to compress the sum for transmission to a distant conference location. A desired signal from a given microphone has a higher level than undesired signals which may be detected by adjacent microphones, so it is emphasized by the associated expander with respect to the undesired signals. The compressor provides compression of the high- and low-level components of the sum in equal proportions so that the former is converted to a replica of the desired signal and the latter is suppressed to acceptable levels.

Abstract: A lower threshold for dynamic range compression and clipping is allowed by sinusoidal estimation and phase adjustment of the original speech signal to obtain a lower Peak to RMS ratio. A sinusoidal speech representation system is applied to the problem of speech dispersion by pre-processing the waveform prior to transmission to reduce the peak-to-RMS ratio of the waveform. The sinusoidal system first estimates and then removes the natural phase dispersion in the frequency components of the speech signal. Artificial dispersion based on pulse compression techniques is then introduced with little change in speech quality. The new phase dispersion allocation serves to preprocess the waveform prior to dynamic range compression and clipping, allowing considerably deeper thresholding than can be tolerated on the original waveform.

Abstract: A digital signal processing method for real-time processing of narrow band signals to provide for reconstitution of dynamic amplitude and harmonics beyond the passband. The method utilizes a digital microprocessor implementing a digital algorithm upon a digitized sample of the analog signals. After processing digital-to-analog conversion circuitry may be used to reconvert the processed digital signal into a processed analog output signal for further use. The digital processing effectively provides a primary voltage compressor (PVC) function for processing signals in m different frequency sub-bands by gain factors, and a summing function for digitally summing the gain products so realized, to provide a primarily compressed signal. The processing method then further effectively provides a secondary dynamic voltage compressor (SDC) function for processing the PVC signal in within n different frequency sub-bands by digitally multiplying signals with each of such sub-bands by gain factors.

Abstract: An FMX stereophonic receiver receives an FMX stereophonic broadcast signal which includes a stereo sum signal, an uncompressed stereo difference signal, and a compressed stereo difference signal which is formed by modulating the uncompressed stereo difference signal by a quadrature modulation and being compressed.

Abstract: A multiband audio frequency signal limiting apparatus suitable for use in a wide range of applications is disclosed. An input signal is divided into discrete frequency bands (any practical number is suitable) which are each passed through a separate limited and subsequently summed to obtain an output signal. The summed output signal is fed into an automatic limit threshold circuit which generates a third signal, the Automatic Limit Threshold (ALT) signal, which modifies a common limiting threshold reference for the bands. This causes the bands to limit at a higher or lower threshold level and the band output levels to increase or decrease in direct proportion to the threshold level of limiting. The ALT signal cause the bands to limit at a lower threshold when the energy content of the various bands would combine toward higher values, which could thus generate a larger than desired output signal level.

Abstract: A stereophonic signal processing circuit is designed to be provided with a pair of level compression circuits compressing peak levels of a pair of stereophonic input signals into 1/2 power each, an arithmetic mean circuit determining an arithmetic mean between a pair of output signals issued from the level compression circuits, and a level expansion circuit expanding a peak level of an output signal from the arithmetic mean circuit into the 2nd power of the level so that an output signal from the level expansion circuit is reproduced midway between individual reproducing positions of the pair of stereophonic input signals. A delay circuit may be connected between the arithmetic mean circuit and the level expansion circuit. The stereophonic signal processing circuit makes it possible to cause more fully the lateralization of a reproduced sound and can be fabricated at a low cost.

Abstract: An improved compansion system that more effectively increases the dynamic range of other circuit elements. The system includes both a compression circuit to limit the input signal amplitude for a circuit element, such as a filter, and an expansion circuit to receive and modify the output of the circuit element. The expansion circuit restores a substantially linear input-output amplitude relationship and may prevent substantial overloading in the circuit element, thereby increasing the dynamic range of the circuit element.

Abstract: In a compressor for controlling the dynamic range of audio signals which comprises an operational amplifier and a gain-controlled amplifier connected in inverse parallel with the operational amplifier, the signal applied to a rectifier for producing the control signal for the gain-controlled amplifier is given an exponential waveform. This can be achieved by the use of two diodes connected in inverse parallel.

Abstract: The device comprises at least one correction circuit interposed in the electroacoustic system and comprising a band-pass filter receiving an input signal, a compressor limiter circuit connected to the output of the band-pass filter, a threshold detector circuit connected to the output of the compressor-limiter circuit and looped thereon in order to allow compression, by said compressor limiter circuit, of the signal issued from the band-pass filter, only if the input signal exceeds a predetermined threshold, and a summing-inverter circuit to which is applied, on the one hand, the signal issued from said compressor limiter circuit, and on the other hand, via an inverter circuit, the input signal applied to the input of the band-pass filter. According to the invention, a plurality of correction circuits can be cascade-mounted, said circuits comprising band-pass filters of which the pass-bands are different but do not necessarily overlap.

Abstract: An FM/FMX stereophonic receiver is capable of receiving an FM or an FMX stereophonic broadcast signal. The FM stereophonic broadcast signal includes a stereo sum signal and stereo difference signal, whereas the FMX stereophonic broadcast signal further includes a compressed stereo difference signal and an FMX ID signal indicating the FMX stereophonic broadcast signal. The FM/FMX stereophonic receiver has a stereo demodulator for receiving said broadcast signal and for producing left and right stereo signals, a detector for detecting the field strength of the receiving signal, and a noise reducer, which may be a circuit for changing the mode from stereophonic mode to monaural mode or a high cut circuit for attenuating the signals of high frequency region, for reducing noise signals contained in the left and right stereo signals.

Abstract: An amplification circuit for hearing aids performs independent amplification of different frequency bands of the signal generated by a microphone of the hearing aid, to match the loss of hearing of a user of the hearing aid. Prior to this multi-band amplification, however, the microphone output signal is passed through an optional filter having a characteristic which is the inverse of the spectrum of long term speech, and through a signal compressor. The signals from the multi-band amplification are combined using an adder and the combined signal is modified by a control signal derived from the envelope of the signal generated by the microphone. The result of this processing is to cause the range of spectral shapes present in received signals to be enlarged or exaggerated in the output signal, but to cause the range of overall levels present in the received signal to be decreased in the output signal.

Abstract: An FM stereophonic broadcasting system incorporating companding of the difference signal in which the broadcast signal includes both the usual difference signal and a compressed version of the difference signal which utilizes, in the transmitter, a circuit for simultaneously compressing the difference signal according to a desired characteristic and modulating the compressed difference signal onto a carrier and, in the receiver, essentially the same circuit for simultaneously demodulating and expanding an incoming compressed difference signal. Simultaneous compression/modulation is achieved by multiplying the difference signal, the carrier signal and a gain control signal, preferably derived from the output signal from the multiplier, for determining the compression characteristic, thereby producing at the output of the multiplier the carrier modulated with the difference signal compressed according to a desired characteristic.

Abstract: In the receiver of an FM stereo broadcasting system which transmits both the usual stereo difference signal S and a compressed version S' of the difference signal compressed according to a compression characteristic such that signals in a lower portion of the audio frequency spectrum are not compressed and signals having frequencies above said portion are compressed, according to a desired characteristic, instead of complementarily expanding the compressed difference signal, only those signal frequencies that have been compressed at the transmitter are expanded.

Abstract: A digital level detecting circuit for controlling amplitudes of digital audio signals is disclosed, which includes a circuit for generating an attack response of output control signals based on positive going waveforms of an incoming signal and attack response coefficients stored in a memory, and wherein the attack response coefficients stored in the memory are limited to a lower value than the theoretical value at the beginning of the attack response.

Abstract: A variable preemphasis/deemphasis network is disclosed which is coupled between audio input and output terminals. The network exhibits a family of transfer function response characteristics which vary between a full deemphasis characteristic H(f) and a full emphasis characteristic 1/H(f) in response to a control signal and exhibits complementary transfer function response characteristics in response to reciprocal valued control signals. The network includes a signal filter which determines the shape of the transfer function response characteristic, and a gain controlled amplifier which determines which one of the family of transfer function response characteristics is exhibited in response to the control signal.

Abstract: A noise elimination circuit, especially for a hearing aid, which removes all sound below a predetermined level and transmits a compressed sound range for all sounds above a predetermined level. The circuit uses a field effect transistor as a voltage variable resistor to transmit a signal when the sound signal is being compressed or is over a predetermined level and block the signal when the sound signal is not being compressed or is below the predetermined level. The field effect transistor drain to source resistance is varied by transmitting a signal indicative of the compression or signal level to the gate of the transistor, such that the gate voltage is higher than the source voltage when signal transfer is desired and the gate voltage is less than the source voltage when no signal transfer is desired. A switch is provided to defeat the noise elimination circuitry.

Abstract: In a stereophonic reproduction system, a true center-channel signal is derived by combining the left and right signals into a monophonic signal, and canceling and overriding this monophonic signal with a second modified monophonic signal, the latter derived by combining properly bandpassed left and right signals that have been compressed, combined, and expanded. True left-and true right-channel signals are subsequently derived by subtracting the true center-channel signal voltage from the left and right signal voltages.

Abstract: A mobile radiotelephone (120) includes a microcomputer (220), speakerphone control circuitry (106) and mobile radio (112). Mobile radio (112) includes a transmitter (242), receiver (244) and a duplexer (243) for coupling the transmitter (242) and receiver (243) to the mobile antenna. In the transmit voice path, speakerphone control circuitry (106) includes switch (201), variable gain amplifier (202), compressor amplifier (203), switch (204), variable gain amplifier (205), and two registers (212-213). In the receive voice path, speakerphone control circuitry (106) includes variable gain amplifier (232), expander amplifier (233), switch (234), variable gain amplifier (235), switch (236) and two registers (216-217). Speakerphone control circuitry (106) also includes rectifier/filter (224), a companding analog-to-digital (A/D) converter (225), two latches (218-219), rectifier/filter (226) and two registers (214-215).

Abstract: A signal processing system is disclosed for processing dynamically varying intelligence-carrying signals represented by different frequencies by transferring these signals within a pass band narrower than the range of the frequencies. The system, although not a compressor or compandor system, makes use of a compressor circuit for compressing only signals within a predefined pass band. Active filter circuits shape the compressed signals into a predetermined power envelope having fundamental frequency signal components and harmonically related constituents of the fundamental frequencies. Another compressor circuit is used for further compressing signal constituents of the power envelope. A negative feedback arrangement provides dynamic limiting of compression by the first compressor circuit as a function of increase of compression by the second compressor circuit.

Abstract: An automatic dynamic equalizer includes left and right input terminals, an input adder and left and right output adders. The left and right input terminals are connected to inputs of the input adder and inputs of the left and right output adder, respectively. The output of the input adder is connected to the input of a 2:1 compressor. The output of the 2:1 compressor is connected to the input of a bandpass filter having a transmission in the low bass frequency region centered at a frequency of about 60 Hz. The output of the bandpass filter is coupled to inputs of the left and right output adders.

Abstract: Circuits for modifying the dynamic range of signals, particularly compressors and expanders for use in noise reduction compander systems, in which the plurality of characteristics are superposed such that as dominant signal components appear, hidden characteristics are revealed and become active. The emergence of characteristics can also be described as "action substitution" in the sense that the action resulting from one, or perhaps more than one characteristic is substituted for one or more other characteristic actions that have the potential to operate in the same frequency and level regions when the level and spectral content of the input signal components change. One particularly useful combination of superposed characteristics is a fixed band characteristic (variable attenuation throughout all or part of the frequency band) and a sliding band characteristic (variable attenuation through part of the frequency band achieved by a variable pass filter).

Abstract: A MOSFET analog signal squaring circuit is disclosed. A first MOSFET has a source electrode coupled to a bias voltage source, a gate electrode coupled to an input terminal, and a drain electrode coupled to an output terminal. A signal inverter is also coupled to the input terminal. A second MOSFET has a source electrode coupled to the bias voltage source, gate electrode coupled to the signal inverter, and a drain electrode coupled to the output terminal. A load impedance is coupled between the output terminal and a supply voltage source.

Abstract: A method for electronically clarifying sound or picture information and an arrangement for carrying out the method. It is previously known to generate harmonics and subharmonics of a useful signal within an audio or video frequency band and to add these to the useful signal in order to improve the perceptibility. Undesirable intermodulation products are generated, however, particularly the difference intermodulation products and the non-linear amplitude ratio between generated harmonic components related to the input signal. The suggested method eliminates substantially all of these undesirable intermodulation products completely and provides a linear amplitude ratio by forming two orthogonal components (X.sub.S,X.sub.C) from the useful signal (X), compressing one or both of these components and multiplynig the result to form the harmonics (2f.sub.1, 2f.sub.2) which are thereafter mixed with the useful signal.

Abstract: A method of (and apparatus for) extending the useful dynamic range of an audio reproduction system. An input acoustic signal in the audible range is transduced to form an analog electric signal which is amplified along parallel paths to gain levels g.sub.1 and g.sub.2 (where g.sub.2 >g.sub.1), the amplified signals being sampled to provide two binary digital signals. The analog signal consists of a high amplitude portion and a low amplitude portion. The two binary digital signals are processed by a computer which provides a first binary output and a second binary output, the first binary output being a digital representation of the sequential samples of the audio signal taken at the respective gain setting g.sub.1 or g.sub.2. More precisely, the first binary digital output is a composite binary digital waveform consisting of a high amplitude portion at gain setting g.sub.1, a low amplitude portion at gain setting g.sub.2 and a transition or cross-fade portion therebetween.

Abstract: A hearing aid having signal compression characteristics that adapt to the environment of the sound field in which it is operative in which an automatic gain control signal processor is responsive to the magnitude, duration and frequency of the signals in a sound field to control a compression amplifier so that the gain thereof is proportional to said signals.

Abstract: A companding system for a television audio apparatus includes a compressor and an expander for stereo difference signals. The compressor provides variable preemphasis of high frequency signal components and the expander provides complementary variable deemphasis. At the receiver, unwanted signals are generated by a mixer that demodulates the stereo difference signal. The unwanted signals can cause mistracking of the expander relative to that of the compressor. A filter to eliminate the effect of these unwanted signals is placed in the expander control circuit, rather than the difference signal path. This eliminates the need and expense of an equalizing filter in the sum signal path.

Abstract: An FM transmission system and method in which a gain control signal is generated and used to encode the audio signal in accordance with a predetermined compression curve. At the receiver the gain control signal is recovered and used to decode the audio signal, thereby providing a faithful reproduction of the original signal regardless of which compression curve is used. The compression curve can be tailored for optimum results for receivers with and without the decoding circuitry, depending upon the program material. The audio signal is delayed in the encoder while the gain control signal is generated, allowing the control signal to fully respond to changes in the audio signal without clipping the audio signal. The gain control signal is segregated from interfering with the remainder of the transmitted signal by restricting it to a low frequency bandwidth centered on the 38 KHz subcarrier for the L-R signal, and placing it in phase quadrature relation to the remainder of the transmitted signal.

Abstract: A signal compression system includes a plurality of channels. A plurality of these channels include a bandpass filter (for filtering out all but a portion of an input signal), an intensity detector (for deriving a spectrally weighted estimate of the intensity of a broader spectral portion of the input signal than the bandpass filtered spectral portion), and a divider (for compressing the bandpass filtered spectral portion using a variable gain having a preselected functional relationship to the spectrally weighted intensity estimate). The signal compression system preserves cross-channel information.

Abstract: Circuits for modifying the dynamic range of signals, particularly compressors and expanders for use in noise reduction compander systems, in which the advantages of fixed band characteristics (variable attenuation throughout all or part of the frequency band) and sliding band characteristics (variable attenuation through part of the frequency band achieved by a variable pass filter) are provided, without the disadvantages normally inherent in each characteristic. Fixed band and sliding band circuit elements are operated either in parallel or in series, the elements operating in generally the same level range and at least a partial overlapping in frequency range.

Abstract: DC signals for controlling variably controlled filters for input audio frequency signals are derived by filtering the input signal to reduce its level in response to variations in intensity and frequency and then logarithmically compressing the filtered signal. An absolute value signal proportionately corresponding to the compressed signal is then derived and combined with an externally generated reference signal of variably selectable level. The combined signal is then converted to a dc variable filter control signal which is blocked when its level falls below the level corresponding to the preselected reference signal level.

Abstract: A noise reduction system which is unaffected by bandwidth limitations of the transmission system with which the noise reduction system is employed. The noise reduction system is of a type including a compressor, the transmission system, which receives a compressed signal from the compressor, and an expander for expanding a signal outputted by the transmission system. In accordance with the invention, a low-pass filter having a pass band corresponding to the transmission band of the transmission system is provided in the stage prior to the compressor. In another embodiment, a low-pass filter is provided in a stage prior to a level detector within the compressor.

Abstract: An audio signal transmission system having a noise reduction circuit, which includes a transmission medium such as a magnetic tape to be used to transmit a digital signal converted from an input audio signal and thereafter to output the audio signal reproduced from the digital signal, a digital signal transmitter having a pulse-code modulator and demodulator (MODEM). The noise reduction circuit includes a compressor for compressing the dynamic range of the input audio signal according to the detection level obtained by detecting at least the high-frequency components thereof in order to supply the output from the compression to the digital signal transmitter and an expander for expanding the dynamic range of the demodulated signal from the transmitter according to the detection level of at least the high-frequency components thereof.