Abstract: This invention relates to an arrangement (14) for protecting a transducer (2) which converts an electric signal into an acoustic or a mechanic signal against overload and destruction. The arrangement is connected to the electric terminals of the transducer and changes the electric input signal under overload condition. This protection arrangement comprises a controller (15), a monitor (16) and an envelope detector (17). The monitor (16) provides a signal indicating the electric or mechanic load of the transducer (2). The peak value of the signal is anticipated by using a predictive filter in the envelope detector (17) or a delay element in the controller (15). If the predicted peak value exceeds an defined limit an attenuation element in the controller (15) is activated and the input signal is changed in time to prevent an overload of the transducer.

Abstract: A digital audio gain control system has an operator interface with a CPU, RAM storage, and input devices for a user to store transfer characteristics relating gain to be applied to an incoming audio signal to the signal strength of that incoming signal. A communication link allows the transfer characteristic function to be sent to a RAM in a separate patchable amplifier unit having a DSP and RAM, and level detection circuitry for monitoring the signal strength of an incoming audio signal and applying gain according to the transfer characteristic communicated to the on-board RAM. The amplifier unit also sends operating information back to the operator interface, where operation may be displayed to aid an operator in adjusting the function.

Abstract: An electronic audio processing system for insertion into the line prior to power amplification and a related method are disclosed which component and method render a frequency response in which undesirably strong frequency bands are flattened relative to the total frequency response by up to 10 dB, thereby providing enhanced dynamic audio reproduction. The audio signal is split into a plurality of frequency bands, each of which is actively, dynamically limited to a predetermined level related to the overall level of the unprocessed signal. The frequency bands are then recombined into a single processed signal which has an overall response which is as much as 10 dB more linearity than the unprocessed signal.

Abstract: An amplifier circuit having a pre-amplifier responsive to a program input signal, a filter circuit, and an absolute value circuit. The pre-amplifier provides automated balancing between the high frequency channel signals and the mid range channel signals to provide a compensated signal. The filter circuit is coupled to receive and automatically filter the compensated signal to provide an output signal and a modified compensated signal. The filter circuit has an adjustable bandwidth that is automatically adjusted in response to the control signal for automatically reducing the bandwidth of the filter circuit in response to lower values of the control signal to obtain the output signal. The filter circuit uses a voltage controlled amplifier or a photo cell in combination with an integrator. An absolute value circuit senses the modified compensated signal and provides a control signal proportional to the average peak value of the amplitude of the modified compensated signal.

Abstract: A hearing compensation system for the hearing impaired comprises an input transducer for converting acoustical information at an input to electrical signals at an output, an output transducer for converting electrical signals at an input to acoustical information at an output, a plurality of bandpass filters, each bandpass filter having an input connected to the output of said input transducer, a plurality of AGC circuits, each individual AGC circuit associated with a different one of the bandpass filters and having an input connected to the output of its associated bandpass filter and an output connected to the input of the output transducer.

Abstract: A signal processing circuit includes two analog signal processors, an operational amplifier, a rectifier, and a reference potential generator. Each analog signal processor has four input terminals and two output terminals, and is designed to operate such that the first and second output terminals are set at the same potential and that a current difference between the first and second output terminals is proportional to a product of a potential difference between the first and second input terminal and a potential difference between the third and fourth input terminal. The first, second, third and fourth input terminals of the first analog signal processor are connected to receive an input signal, a first reference potential, a second reference potential, and a third reference potential, respectively. The output terminals of the first analog signal processor are connected to the negative and positive input terminals of the operational amplifier, respectively.

Abstract: In a dynamic noise reduction system, the release time versus frequency bandwidth is exponentially related and well beyond that achievable with a simple RC circuit.A dc control signal is derived from an input audio frequency signal by peak detecting the input signal, filtering the peak detected signal and controlling the release time of the filtered signal so that its release time is fast when the frequency is within a predetermined high range, its release time is moderate when the frequency is within a predetermined intermediate range and its release time is slow when the frequency is within a predetermined low range.

Abstract: An improved audio compressor of the type which is used in a hearing aid and having a programmable compression ratio is disclosed. In the preferred embodiment, the compressor includes a variable gain limiter which provides variable gain amplification of the input signal and as a further function of a programmable control signal. A feedforward circuit is disposed in parallel to the variable gain limiter and provides a fixed gain signal. The output of the limiter and the feedforward circuit are combined at a summing node, which serves as an output. The gain curve of the compressor defines a sigmoid function having a pivot midway between the upper and lower break points.

Abstract: An audio compressor using interactive layered time constants to create an easy to use compressor which self adapts to the program characteristics and provides a desirable and pleasing effect over a wide range of audio program material. The audio compressor includes an adaptable filter connected between an output signal path and a control feedback signal path of a voltage control amplifier. The adaptable filter comprises a first resistor-capacitor circuit connected to the output signal path and producing a charging/discharging voltage which is more dependent on a transient peak value of the audio signals and a second resistor-capacitor circuit working under the charging/discharging voltage of the first resistor/capacitor circuit for producing a charging/discharging voltage which is more dependent on an average value of the audio signals.

Abstract: An audio signal has its dynamic range compressed by a system which first samples a block of the audio signal (10), typically several seconds long. The level of the signal in this block is analyzed (12, 14) and an ideal signal level is calculated for the block (16, 18, 20). A gain control signal is then derived which adjusts the gain applied to that block towards that required to give the calculated ideal signal level.

Abstract: Selectively compressing the signal supplied to a loudspeaker based upon the volume setting for the sound level to be produced by the loudspeaker improves the intelligibility of human speech produced by a loudspeaker at high volume levels. Compression of the signal to the loudspeaker prevents the loudspeaker from overloading. The level of compression may be adjusted based upon the volume setting. The amplitude of an audio signal sent to a loudspeaker may be increased if below a preselected pivot point and increased if above the pivot point. The amount of increase or decrease in the amplitude may be proportional to the difference between the amplitude of the audio signal and the pivot point. This difference may also be raised to the power of a shape factor to determine the amount of increase or decrease in the amplitude of the audio signal.

Abstract: A peak accelerated compressor comprising a voltage controlled amplifier, a level detector and a peak accelerated filter circuit. The voltage controlled amplifier circuit is utilized for processing an input audio signal and producing an output audio signal. The level detector circuit is utilized for processing a sample audio signal which contains transient peaks and average waveforms. The peak accelerated filter circuit is coupled between the level detector circuit and the voltage controlled amplifier circuit for producing a control output signal to change the gain of the voltage controlled amplifier circuit in response to the transient peaks in the sample audio signal. The peak accelerated compressor effectively enhances the compression for transient peaks without adversely affecting the normal compression of average waveforms.

Abstract: An audio compressor having both a feedback compressor and a feedforward compressor. The feedback compressor operates so as to provide envelope detection. A sidechain processor which receives an input from the feedback path includes a non-linear low-pass filter and a non-linear amplifier. The output of this processor provides the gain-control signal for the feedforward compressor. The main audio path is through the feedforward compressor.

Abstract: An analog signal to be delayed thereby is compressed according to a monotonously increasing, convex compression function and sent to a delay circuit constituted digitally. Data of a digital value stored in a memory is read out after a constant delay time and converted into an analog signal by a D/A converter. The analog signal is expanded according to a reverse function of the compression function to restore it as an echo signal.

Abstract: A circuit and method for mixing signals from audio sources provide noise reduction by employing a noise gate to selectively attenuate one of the source signals. The noise gate has a low gain state and a unity gain state. The noise gate switches to its unity gain state when a control signal reaches a predefined threshold voltage. The control signal is generated by rectifying and integrating the noisy source audio signal, so that the noise gate enters the unity gain state only when a useful sound occurs. Thus, the noise in the combined audio signal is reduced, without attenuating useful components of the source signals.

Abstract: The present invention relates to a correcting apparatus of sound signal distortion by way of an audio frequency pass segmentation, the apparatus comprising: frequency band segmentation means for segmenting an audio frequency band sampled by a predetermined frequency into a plurality of bands; decimation means for performing a decimation in respectively different ratios in accordance with a sound data band band-segmented by the frequency band segmentation means; distortion correcting means for performing a distortion correcting on the sound data decimated from the decimation means per band; and data output means for synchronizing the sound data distortion-corrected at the distortion correcting means so that the sound data can be in the same order as the sound data when input to the frequency band segmentation means to thereby b output in synthesis.

Abstract: An audio electronic volume controller (100; consisting of a ladder resistance and a CMOS switch group) and an output buffer (B2) are formed within an identical semiconductor substrate 10S, and nodes (N.sub.31 and N.sub.31) are directly connected by a wiring layer (31). An input differential circuit element of an operational amplifying element which is a main unit of the output buffer (B2) is configured using MOSFETs. Accordingly, input bias current and floating impedance can be decreased which leads to a decrease in the generation of click noise.

Abstract: A sound gain control device for automatically controlling a gain by which an output signal from a sound CODEC is multiplied is provided. Sound signals from a sound input device are processed by a non-linear conversion circuit so that the sound signals with small amplitudes are enlarged by extending the amplitudes and the time axis thereof, thereby to average the incidence probabilities of amplitudes. Then, a proper amplitude for a gain control is calculated based on the averaged signals by an amplitude calculating circuit, and a gain corresponding to the calculated amplitude is determined by a gain determining circuit and sent as a amplitude coefficient to a multiplier to which the sound signals from the sound input device are input through a sound CODEC.

Abstract: A circuit automatically adjusts in response to an input audio signal to provide a dc control signal having the release characteristics of the input audio signal. The circuit has an input reference node for receiving a reference signal which is a function of the input signal, an output reference node for providing the dc control signal and an intermediate reference node between the input and output reference nodes. One or more diodes connected between the input and intermediate nodes permit forward conduction from the input node to the intermediate node. Components of a first signal path connected between the intermediate and output nodes provide a slow release time when the reference signal has a slow decay envelope.

Abstract: A headset amplifier, adapted for use with a voltage source such as a battery, includes a time-out-timer circuit for deactivating the headset amplifier after a first predetermined period of time and for reactivating the amplifier in response to a signal fed to an input port of the time-out-timer circuit.

Abstract: Method and device for transposing the frequency of an input signal, in particular for hearing aids, comprising:an analytical circuit (AS) with which are produceable a momentary frequency signal w(t) whose strength is proportional to the momentary frequency of the input signal u.sub.i (t) and a momentary amplitude signal A(t) whose strength is proportional to the momentary amplitude of the input signal u.sub.i (t);a voltage-controlled oscillator (VCO) which is connected to the output of the analytical circuit (AS) that supplies the frequency signal w(t);a multiplier (M) with two inputs, of which one of them is connected to the output of the voltage-controlled oscillator (VCO) and the other to the output of the analytical circuit (AS) supplying the amplitude signal A(t).

Abstract: This invention includes a compression circuit for compress one of an audio signal and a mixture of the audio signal and an echo signal, a delay circuit for delaying an output signal of the compression circuit by a predetermined time and an expansion circuit having a conversion rate controlled by a DC voltage generated correspondingly to a regulation of the volume controller, for expanding the output signal of the delay circuit according to a reverse conversion function to the compression conversion function to generate the echo signal.

Abstract: An expander circuit for decoding audio signals which were encoded in accordance with the BTSC multichannel sound system standard including DBX commanding is presented. A wideband expander circuit is utilized and a DBX expander can be accommodated. The wideband expander circuit is provided with a signal path having an input LPF (low pass filter), a stereo difference signal (L-R) demodulator, a second LPF, and a voltage controlled amplifier (VCA), the gain of which is controlled by a control signal derived from the demodulated difference signal which has been operated on by a bandpass filter (BPF) and an integrating peak detector. The output of the VCA is provided to a deemphasis network before being fed to a decoder matrix for combining with the sum stereo signal (L+R) for reconstructing the original L and R signals.

Abstract: An expander circuit for decoding audio signals which were encoded in accordance with the BTSC multichannel sound system standard including DBX companding is presented. A wideband expander circuit is utilized and a DBX expander can be accommodated. The wideband expander circuit is provided with a signal path having an input LPF (low pass filter), a stereo difference signal (L-R) demodulator, a second LPF, and a voltage controlled amplifier (VCA), the gain of which is controlled by a control signal derived from the demodulated difference signal which has been operated on by a bandpass filter (BPF) and an integrating peak detector. The output of the VCA is provided to a deemphasis network before being fed to a decoder matrix for combining with the sum stereo signal (L+R) for reconstructing the original L and R signals.

Abstract: A device for enhancing the bass frequency components in an audio signal while avoiding overload problems associated with fixed levels of bass frequency enhancement. The device divides the input signal into two parts, the first of which passes through to the output of the device. The second part of the input signal is input into a low pass filter which passes only the bass components of the input signal and imparts a frequency dependent phase shift to the bass components. The bass components then pass through a variable gain amplifier which may or may not invert the polarity of the bass components and then are recombined with the first part of the audio signal. The gain of the variable gain amplifier is varied in accord with the level of the bass components.

Abstract: In a hearing aid having a switched amplifier, an amplifier circuit is provided so that the pulse amplitude of the switched output signal is adjusted as a function of the envelope of the audio signal to be amplified. A controllable amplifier is switched in series ahead of the switched amplifier, whereby its control by the audio signal to be amplified proceeds in such a manner that the product of the amplifications of the two amplifiers remains constant for all audio signal levels.

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: An audio frequency compressing system for amplifying an input signal to produce a power output signal while removing high-level signals which could harm a listener. Gain control in the feedback path of an amplifier includes both a gain controller circuit for supplying a constant feedback impedance and a plurality of resistors which can be coupled to the gain controller circuit to increase or decrease the feedback impedance. Coupling of the resistors to the gain controller circuit is controlled by a feedback control circuit having both an automatic gain control circuit and a continuous high-level protection circuit.

Abstract: The invention relates to a compressor and an expander for use in a compander realized in CMOS-technology which is used to improve speech quality in mobile phone systems AMPS (NAMPS), NMT and TACS (JTACS, ETACS, NTACS). The compander is integrated with other functions of the mobile phone. The compressor and expander have SC-amplifiers controlled by a control logic. A double comparator XOR-block is used in the control of the amplifiers.

Abstract: An automatic gain controller uses a voltage controlled amplifier coupled to an averaging circuit that feeds back into the amplifier. The averaging circuit supplies a controlling voltage that keeps the amplifier output voltage tending towards a certain reference level. When the amplifier output is generally high, the averaging circuit output is also generally high and the reverse is also true for low signals. For low averaging circuit output voltages corresponding to low intensity signals, amplification of the signal by the amplifier is enhanced or augmented. The result is to boost the signal of low intensity signals significantly, compressing the dynamic range of an incoming signal received from a phone. This reduces the variance of an incoming phone line signal for an analog to digital converter (ADC) in a digital telephone answering device, and the effective dynamic range of the ADC is closer to optimum. A scaling circuit couples the signal from the automatic gain controller to the ADC.

Abstract: An improved audio compressor of the type which is useful in a hearing aid and having a programmable compression ratio is disclosed. In the preferred embodiment, the compressor is used in a hearing aid device of the type which comprises a bandsplit filter to divide an input audio signal into a plurality of frequency bands. Associated with each frequency band is a limiter means which provides variable gain amplification of the input signal as a function of the amplitude of the input signal and as a further function of a programmable control signal. A feedforward means is disposed in parallel to the limiter means, said feedforward means providing a fixed gain signal. The output of the limiter means and the feedforward means are combined at a summing node which forms the input to a variable gain amplifier. Associated control circuitry allows the limiter gain to be programmed to meet the needs of an individual user. The compressor has a variable compression ratio in the form of a sigmoid function.

Abstract: A device and a method for processing an analog input signal (S) which varies widely in amplitude, such as speech, for the purpose of reducing the ratio of maximum to minimum amplitude variations of an output signal (P), after the processing, to the square root of the ratio existing before processing in order better to transmit said signal through a channel of restricted dynamic range in the presence of additive noise. The device comprises a converter (2) arranged to change the input signal (S) into a stream of integer numbers (N1,N2,N3 . . .). The numbers in the stream represent in some proportional way the instantaneous value of the input signal (S) divided by a reference voltage (R). This reference voltage (R) is generated by a smoothed amplitude measuring device (4) in proportion to the amplitude of the output signal (P) that is produced, when the number stream is reconverted to an analog signal waveform by means of a converter (6) working with a constant reference voltage.

Abstract: A circuit for conditioning an input signal containing audio and noise components is provided in which a first circuit branch is used for deriving a first DC signal proportionate to the decibel level of high band information in the input signal and a second circuit branch is used for deriving a second DC signal proportionate to the amplitude of the input signal. A preselected maximum threshold reference is provided when the second DC signal drops below a preselected threshold and also for a predetermined time period when the second DC signal rises above the preselected threshold. The first DC signal and the maximum threshold reference are used to provide a peak detector signal input which is maintained at a level equal to the most negative level of the first DC signal when the maximum threshold reference is not provided and at a level equal to the most positive level of the first DC signal but not greater than the preselected maximum threshold reference when the maximum threshold reference is provided.

Abstract: A signal processing circuit in an audio device includes a variable gain control section for providing a variable amplification gain to an input signal in response to a gain control signal, an input signal level detecting section for detecting a level of the input signal and for generating a corresponding detection signal, and a time constant setting section for storing a plurality of time constant tables. Each one of the plurality of time constant tables includes a set of input signal delay characteristics corresponding to a predetermined level of the input signal. A time constant selecting section selects one of the plurality of time constant tables in the time constant setting section in response to the detection signal. The gain control signal is determined by the selected one of the plurality of time constant tables and the amplification gain of the variable gain control section is varied according to the selected one of the plurality of time constant tables.

Abstract: A compandor circuit uses a DC-coupled compressor to reduce the required IC package size to 8-pins. A delta gain stage and rectifier in the feedback path of the compressor circuit receive the AC and DC components of the compressed analog output signal Features of the delta gain stage and rectifier eliminate the need for any AC-coupling capacitors in the feedback path thereby reducing the number of external components The remaining external components may be made smaller and manufactured as surface mount devices An expandor circuit receives a second compressed analog signal and expands it to full amplitude dynamic range.

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: An operational amplifier (1) and resistors (11) and (12) damp an input signal (V.sub.1) by -6dB. Since a positive input terminal of the operational amplifier (1) is fixed at -3V, DC component of the input signal (V.sub.1) is down-shifted to -3V so that a signal (V.sub.2) is obtained. The signal (V.sub.2) is inputted to an electronic volume (100) wherein the signal (V.sub.2) is damped thereby a signal (V.sub.3) is obtained. An operational amplifier (2) and resistors (13) and (14) amplify the signal (V.sub.3) by 6dB. Since a positive input terminal of the operational amplifier (2) is fixed at OV, DC component of the signal (V.sub.3) is up-shifted to OV thereby a signal (V.sub.5) is obtained. The signal which is to be processed in the electronic volume has only a half voltage relative to that of the input signal.

Abstract: For facilitating the transmission or recording of digital audio signals in a narrow band channel or at a reduced data rate without deterioration of audio quality detectable by the human ear, a digital audio signal is subdivided into overlapping time window segments and the segments are subjected to fast Fourier transformation, with generation of scaling factors. The spectral values resulting from the transformation are converted into separate magnitude and phase values, the former being logarithmically quantized and the latter being linearly quantized. The magnitude values corresponding to an upper portion of the spectrum are collected into groups of a size that increases towards the high frequency end of the spectrum and the magnitude values of each group are rms averaged, so that one value can serve in place of several magnitude values, thereby reducing the data to be transmitted or recorded.

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: An audio signal energy level detector for use with audio signal processing is described. The energy level detector includes a high-pass filter series-connected between an audio input signal and a series-connected rectifier and integrator the output of which is connectable to the control input of a variable gain device that processes the audio input signal. A characteristically -10 db/decade amplitude versus frequency slope audio input signal is high-pass filtered, rectified and smoothed to produce a constant-energy, DC gain control signal. When the audio input signal is processed in accordance with the invention by the variable gain device to produce an audio output signal suitable for dynamic, downstream processing, the tonal balance and timbre of the audio input signal are preserved. Passive and active, half-order, five-stage high-pass filters are described that provide the desired +10 db/decade amplitude versus frequency slope over the audio frequency range.

Abstract: Apparatus for reducing distortion in a peak limited audio siganl. The amount of low-frequency spectral energy in the input audio signal is determined for a peak limited signal and used to control low-frequencies in the output audio signal. Identical low-pass filters with cut-off frequencies of 2.2 kHz are used; one passing a peak limited signal, the other a non-peak limited signal. When no noticeable low-frequency spectral energy is present in the peak limited (clipped) signal, the peak level is controlled below 2.2 kHz, without distortion, by a VCA and above 2.2 kHz by a clipper. When low-frequency spectral energy is present, the VCA reduces gain on each low-frequency wave to prevent uncontrolled safety clipping.

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: A system is provided for use with an electrical musical instrument for conditioning electrical signals generated by the instrument and for creating controlled distortion. The system includes an amplifier circuit having an input for responding to the signals and an output to provide a conditioned output signal. There is included at least one bandpass filter for frequency preemphasis of the input signal. A limiting circuit is operatively connected to the bandpass filters limiting the amplitude of signals received from the bandpass filters to produce a relatively high distorted, long sustained signal. A notch filter operatively connected to the limiting circuit reduces the heavy mid-range frequency content produced by the combination of the bandpass filters and the limiting circuit. A low pass filter operatively connected to the notch filter further conditions the signal generating a conditioned output signal.

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: An audio compression system wherein the compression theshold may be adjusted to a calibrated level. The audio compression system is utilizable in a receiver system whereinan audio input signal received by the receiver system via a communications channel is applied to conditioning circuitry. The conditioning circuitry, in turn, provides a conditioned input signal to an acoustic transducer element for generating a corresponding audio output signal. The audio compression system compares the conditioned input signal and an initial threshold signal to provide a comparator output signal corresponding to the difference between the conditoned input signal and the initial threshold signal. The comparator output signal is provided as a control input to the conditioning circuitry. If the conditioned input signal exceeds the initial threshold signal for a preselected period of time, then the initial threshold signal is switched to a second threshold signal.

Abstract: A noise reduction apparatus in an FM stereo tuner including a circuit for generating a stereo sum signal and a stereo differential signal; a noise eliminating circuit for dividing, in accordance with several frequency bands, the stereo differential signal into several divisional signals and for outputting, in accordance with signals levels corresponding to the frequency bands, a composite signal of divisional stereo differential signals respectively corresponding to the signal levels; and a circuit for reproducing a stereo signal from the composite signal and the stereo sum signal.

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.