Abstract: An audio processing method is described wherein an audio input signal is delayed and then submitted for signal processing. The signal is sampled prior to the delay and control parameters for speech compression, voice gating, and voice activation of ancillary equipment generated. The delayed audio is then processed according to the parameters determined prior to the delay to eliminate poor transient response and signal clipping.

Abstract: Three related embodiments of audio signal dynamic range circuits for consumer and semi-professional audio signal compressors, expanders, and compressor/expander noise reduction systems incorporate certain basic features of professional Spectral Recording (SR) while adapting SR for use with consumer recording media (particularly audio cassette tape) and reducing the cost and complexity of the SR circuitry. In addition, the three embodiments, and particularly the preferred embodiment, provide substantial compatibility with the existing B-type and C-type consumer and semi-professional noise reduction systems. Subjective performance substantially equivalent to 16-bit PCM audio systems is achieved with analog audio cassette tape media.

Abstract: A compandor system is provided that uses integrated circuitry in combination with fully external controlling devices for unity gain level adjustment without affecting the dynamic range. In addition, the system's stability is maintained. The external control is provided, for instance, by replaceable discrete resistors.

Abstract: An input signal representing speech is preamplified, filtered, and fed foward in parallel to Automatic Gain Control (AGC) circuitry and to a gain controllable amplifier. The AGC detects the peak absolute value of the input signal, charing a capacitor in accordance with such detections. The capacitor is discharged at a faster rate (variable down to 1 msec) when a greater charge value is stored but at a slower rate (variable up to 4 seconds) when a lower charge value is stored. The gain controllable amplifier is controlled for gain inversely to the charge value stored on the capacitor. The AGC captures greater than 60 dB of allowable input signal range, compressing such input signal into a (controllable) limited amplitude dynamic range.

Abstract: Data communication nodes in a network comprising a plurality of nodes linked together to form communication paths negotiate by passing messages to identify to one another the maximum supportable degree of data compression capability. Logical comparisons are made at each node between indications received from upstream and downstream nodes, if any, regarding their own or their received indications of data compression capability with the present node's own degree of compression capability. This enables logical decisions to be made to suport the maximum degree of compression capability over each link or portion of a link between terminal nodes which define the ends of the overall link, thus improving data transmission by providing the highest degree of supportable compression over the longest path length.

Abstract: A composite signal processor and single-ended noise reduction system uses a split input to the single-ended noise reduction circuit in such a manner that the audio signal from the output of the signal processor circuit is dynamically filtered in response to a control signal derived from the unaltered audio signal prior to signal processing. User selective switching is also provided to permit the signal processor and the noise reduction circuit to be used simultaneously or independently.

Abstract: An audio signal compression device which utilizes both a broad band compressor and a high frequency expander. The level of the compression provided by the compressor and the level of expansion provided by the high frequency expander are both controlled by a voltage or other signal that is output by signal level detection circuitry within the device. The broadband compressor provides a variable level of amplification (or attenuation) that is relatively uniform as a function of frequency. The high frequency expander provides a variable level of expansion wherein the high frequency components are expanded more than the mid and low frequency components.

Abstract: A linked compressor-expander (Lincompex) system and method varies the power of the control tone signal to maintain the power of the signal supplied to the transmitter substantially constant. The system measures a parameter related to the power level of the compressed information signal output from the compressor and varies the power of the control tone such that the sum of compressed information signal power and control tone power is substantially constant. When the input information signal drops below the compression range of the compressor, the control tone amplitude is thereby boosted to maintain the combined information signal and control tone signal power more nearly constant, and thus improve performance during low input information signal power levels. During these low input information signal power levels, the power of the control tone S/N is boosted so as to maintain higher control tone at the receive, thereby improving demodulator performance.

Abstract: A decoding arrangement for decoding audio signals previously encoded in accordance with the dbx format, includes a wideband expander instead of a full dbx expander. The wideband expander employs a relatively simple, and therefore inexpensive, peak detector in place of the true RMS detector of a full dbx expander, and does not include apparatus for spectral expansion of the audio signal. Although the decoding is noncomplementary with respect to the encoding, the stereo audio reproduction as perceived by a listener, is surprisingly good.

Abstract: A linked compressor-expander (Lincompex) circuit for use in telecommunications utilizes a frequency compensation circuit to frequency shift the total bandwidth of the whole communication channel to eliminate single side band "duck-talk" and data distortion in the transmitting of a complex waveform due to frequency drift or the detuning of the transmitter/receiver system. The demodulator includes an expander for expanding the compressed voice or data signal and a control tone conversion circuit for converting the received control tone into a frequency signal to be used by the expander. The control tone conversion circuit also determines the frequency error of a combination information waveform so that the frequency compensation circuit can carry out the proper frequency shifting process. A fading regulator is also provided to remove any audible level variations not removed by the automatic gain control circuitry in the receiver.

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 desired non-linear, monotonic compression function is performed substantially symmetrically upon both polarities of an AC signal by a circuit having a plurality of limiting stages, each having input circuitry with like terminals connected in parallel to one another, and providing an output current proportional to the stage input voltage, with a gain constant decreasing for an increasing stage number. Each stage has output circuitry connected in parallel with one another and providing an output current proportional to the stage input voltage, with a gain constant decreasing for an increasing stage number. A single output stage converts the total current provided by the limiter stages to an output voltage.

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: 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: A method and apparatus for reducing noise fluctuation in a linked compressor-expander (Lincompex) telecommunications system in which an artificial tone signal is injected into a demodulator of the communication system to bias the output toward self quieting. The artificial tone is developed to have a level that is effective below a threshold level of Lincompex demodulation such that during normal communication transmission, the artificial tone has no deleterious effect, while below the demodulation threshold, random noise inputs are effectively biased to a constant level to produce a quieting effect on the demodulator output.

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: A method and circuitry are disclosed for suppressing additive transient disturbances in a data channel; e.g., due to thermal transients caused by an MR transducer contacting moving a storage surface. Positive and negative envelope detectors each have their inputs connected to the channel, and provide respective outputs which are summed and contain an envelope component and a residue component. A buffer interconnects the detectors to allow both detectors to follow rapid positive excursions of the data channel signal. A nonlinear signal-adaptive filter is connected to the summed output to further reduce the residue component. The data channel signal (or preferably the output from a delay means connected to the channel) is summed with the output from the filter. The relative amplitudes of these two outputs is set such that the resulting summed output signal is free of additive disturbances.

Abstract: A system is provided for use with an electrical musical instrument for conditioning electrical signals generated by said instrument. Said system comprises an amplifier circuit having input means for responding to said signals and output means for providing a conditioned output signal, and at least one compressing means operatively connected to said input means for responding to the amplitude of said electrical signals to provide a compressed signal to said amplifier circuit that is variable as a nonlinear function of said amplitude.

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 digital non-linear pre-emphasis/de-emphasis apparatus is arranged such that a frequency band of a high-pass filter for extracting a high frequency component signal of an input signal is varied according to the input signal by feeding back the output signal of the high-pass filter through a first non-linear input/output circuit. The first non-linear input/output circuit multiplies the output signal of the high-pass filter by a coefficient which is a function of the output signal of the high-pass filter to obtain a feedback signal. The output signal of the high-pass filter is also applied to a second non-linear input/output circuit which multiplies the output signal of the high-pass filter by a coefficient which is a function of the output signal of the high-pass filter. An output signal of the second non-linear input/output circuit is mixed with the input signal by an operation circuit to obtain an output signal which is non-linearly emphasized or de-emphasized.

Abstract: In storing digital tone waveshape data in a waveshape memory, sampled tone waveshape data is stored in the memory by previously elevating the level of frequency components in a predetermined high frequency region. This predetermined high frequency region corresponds to a frequency region to which quantization noise components belong. The tone waveshape data stored in the waveshape memory in this manner has the signal level of the component of the region including the quantization noise components reinforced as compared with the original tone waveshape. The tone waveshape data read out from the waveshape memory is applied to a filter of a characteristic which restrains the level of the component in the predetermined high frequency region. The level of the quantization noise components belonging to the predetermined high frequency region contained in the tone waveshape data thereby is restrained.

Abstract: A digital linked compressor-expander telecommunications system (Lincompex), is implemented using a general purpose digital signal processor wherein the compression and expansion functions are performed by blocks of programmed code. Input audio analog signals are converted to parallel data digital signals thereupon the digitial signals are input for processing. After processing, the resultant signals are passed to a 16-bit digital-to-analog converter where either the compressed or expanded digital voice data signal is converted back into an audio frequency analog signal for either transmission or communication on an output device.

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: 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. The outputs of fixed band and sliding band circuit elements variably selected by a combining means operated by a control circuit which senses signal frequencies and/or levels, the elements operating in generally the same level range and at least a partial overlapping in frequency range.

Abstract: When impedance elements such as FETs are used in attenuators, the elements have linear responses only when the signals attenuated are below certain signal levels. When signal conditions causing the element to operate non-linearly are detected, bootstrapping is applied to reduce the voltage across the element so that the element will operate linearly. The control signal at the gate of the element is then modified to compensate for the increase in effective impedance of the element caused by bootstrapping. The improved attentuators are especially useful in signal compressors and expanders.

Abstract: A variable resolution system for a potentiometer converts the analog output of the potentiometer to digital steps which are multiplied to provide a number of digital output steps dependent upon the extent of potentiometer movement since last reversal. Upon each reversal, the number of output steps per input step is reduced to provide greater resolution.

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: The drain-source conductance of a wide variety of FETs can be made to conform to a predetermined function of a control signal. The control signal is multiplied by a factor and an offset is added or subtracted therefrom to derive a modified control signal. The modified control signal is then applied to the gate of a FET. The factor and the offset are such that the drain-source conductance of the transistor is substantially the predetermined function of the control signal. When a desired attenuator characteristic defined with respect to a FET is to be provided using a FET having characteristics different from those of the reference FET, the control signal to the FET used can be similarly modified so that the desired attenuator characteristics are obtained.

Abstract: A gateway circuit which exchanges information between a leased-line information transmission system and a power line carrier information transmission system includes a control circuit which receives and formats information transmitted over the leased-line information system and a separate control circuit which receives and formats information received over the power line carrier system. The formatted information is provided to a third control circuit which buffers the information and converts between the leased-line format and the power line carrier format to enable signal exchange between the two information transmission systems. The general control circuit responds to load control commands generated by manual switches located on the control unit and to load control commands forwarded over the leased-line system.

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: The clipping suppression arrangement for a compandorized communication system, includes a limiter peak level detector for causing the gain of an input amplifier to be reduced quickly when a compressed output is driven toward a clipping output condition.

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 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 non-linear signal processing apparatus used in a video tape recorder or a video disk player is disclosed. The time variation of an input signal or a processed version thereof is non-linearly processed by a differential circuit and a closed loop including a non-linear circuit. The non-linearly processed time variation of the signal or a processed version thereof is arithmetically combined with the input signal. Thus, the same non-linear characteristic as that obtained by the prior art analog signal technique is attained by the digital signal processing technique, which is superior in integrity and stability. By appropriately selecting the characteristic of the non-linear circuit, better results than those obtainable by the analog signal processing technique are achieved.

Abstract: A logarithmic compression circuit comprising an operational amplifier and a transistor for logarithmic compression. One of the emitter and collector of the transistor is connected to the inverting input of the amplifier and the other of the emitter and collector of the transistor is connected to the output of the amplifier. A switching device is selectively connected between the base of the transistor and the non-inverting input of the amplifier and between the base and the said one of the emitter and collector of the transistor in accordance with the magnitude of a signal current input.

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: 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: 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: The complementary pre-processing and post-processing circuits of this inventiona re advantageous for reducing noise introduced into a signal by a process or medium where the noise introduced rises with the signal level. The pre-processing circuit analyzes the spectral composition of an input signal and generates an emphasis control signal to so indicate. The emphasis control signal is limited by a limitation circuit to a desired bandwidth. The pre-processing circuit includes an emphasis applying circuit for amplifying or attenuating the input signal as a function of the emphasis control signal. A delay circuit delays the input signal relative to the emphasis control signal so that the input signal reaches the emphasis applying circuit when the emphasis control signal is available for controlling the amplification or attenuation applied.The post-processing circuit restores the spectral composition of the signal.

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 voice switched gain system is disclosed for loudspeaking telephone and hearing aid applications involving electret microphones. A voice switched gain circuit comprises an audio pre-conditioning circuit for providing a conditioned audio input referenced to an unconditioned audio input to a compandor circuit. A linear gain level reference generator circuit generates a level for comparison with the audio input level. A decision circuit then controls the compandor operation based on the result of the comparison. The decision circuit either maintains the audio output of the compandor in a compressed state or expands the audio input signal to a higher level expanded state for transmission. Two such circuits are provided in a loudspeaking telephone system, one circuit for maintaining a preemptive near end control through appropriate timing of the dual decision process. Far end control is provided by the other voice switched gain circuit.

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.

Abstract: A non-linear digital emphasis circuit for non-linearly emphasizing a high frequency component of an input digital video signal in accordance with an amplitude of the digital video signal. This emphasis circuit comprises: a digital filter for emphasizing the high frequency component of the digital video signal; and a memory in which a data conversion table to non-linearly compress the amplitude of the digital video signal is written and to which the digital video signal is supplied as an address input. The respective polarities of the address input of the memory and of the readout output therefrom are inverted by a polarity inverter in accordance with the polarity of the digital video signal. With this emphasis circuit, an error of the frequency characteristic and time and temperature changes thereof are not caused and no adjustment of the characteristic is needed. Also, this circuit can be formed as an integrated circuit by utilizing only digital circuits.