Abstract: Improved FMX Companding apparatus for FM transmitter. A pilot subsystem which is substantially identical to the FMX audio path is used to develop a control signal which provides amplitude control through a VCA in the main FMX audio path.

Abstract: A companding system for a television audio apparatus includes a compressor and an expander for stereo difference or second audio program signals. The compressor provides variable preemphasis of high frequency signal components and the expander provides complementary variable deemphasis. Due to noise, the amount of deemphasis the expander can provide is limited. To ensure complementary operation of the compressor and expander a clamp means is used in the compressor to set the maximum amount of preemphasis. Similarly, in the expander, a clamp is used to set the maximum deemphasis of the compressor.

Abstract: A method of and apparatus for processing audio signals in which a measure of amplitude of audio signals in a selected time period is obtained. The audio signals for the selected time period are delayed until the measure of amplitude is obtained, and then the delayed audio signals are normalized using the measure of amplitude. High-frequency emphasis may be employed prior to obtaining the measure of amplitude. Alternatively, a multi-channel system can be employed for processing audio signals in limited frequency bands. The method and apparatus are applicable in a variety of applications including hearing aids, audio storage media, broadcast and public address systems, and voice communications such as telephone systems.

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 in two ways to enhance system noise reduction. First, the compressed signal is expanded at a constant ratio over all signal levels so that low level mistracked signals are further deemphasized and the system noise floor is lowered.

Abstract: Method and apparatus for aiding hearing are disclosed comprising an automatic gain control unit which includes a first section for increasing the amplitude of input signal segments that are below a threshold level, and a second section for reducing the amplitude of input signal segments that are above said threshold level. Both sections have short attack and long release time constants. A long attack short release time constant noise suppressor unit responsive to the output from the second section and having a threshold level of operation below that of the threshold level of the automatic gain control units passes speech signals and squelches background noise signals between speech signal segments for improved understandability of speech signals.

Abstract: In an electronic audio signal processor suitable for electrical instruments such as electrical guitars, there is provided an improved pre-amplifier and compressor circuit which compresses the amplitude level of an inputted audio signal so as to provide lower noise better weak note recovery and improved high end boost, for low volume signals when the output thereof is fed through a distortion amplifier. The compressor circuit includes an op amp and feedback FET transistor.

Abstract: A video signal processing apparatus has an input terminal for receiving an input video signal and a delay line for delaying the input video signal. A first transmission circuit processes the video signal which has been delayed by the delay line and a first timer reversal circuit reverses the time sequence of the input video signal during a predetermined time period. A second transmission circuit processes the time reversed signal from the first time reversal circuit and a second time reversal circuit reverses the time sequence of the signal processed by the second transmission circuit. An adder circuit adds the signal processed by the first transmission circuit and the time reversed signal from the second time reversed circuit. A control pulse generator produces a control pulse sequence which inverts its level every predetermined period so as to control the first and second time reversal circuits. The output of the adder circuit serves as the output signal processing apparatus.

Abstract: A noise reduction system including a signal path (34) between an input terminal (12) and an output terminal (36), a voltage control amplifier (38) and a control path (40) between the input terminal and the voltage control amplifier is disclosed. A nonlinear element such as a voltage squarer (32) is in the controlled path. In one arrangement, the control path also includes a signal level detector (22), a one-pole high pass filter (16) and a direct current level shifter (26). A precision diode (30) is interposed in the control path between the direct current level shifter and the signal squarer. One form of the noise reduction system includes a voltage-controlled low pass filter (20) interposed in the signal path between the input terminal and the voltage-controlled amplifier. A weighing control path (46) provides the control signal for the voltage-controlled low pass filter. A two-pole high pass filter (18) followed by a level sensor (48) is interposed in the weighting control path.

Abstract: A stereophonic broadcasting system incorporating companding of the difference signal in which both the usual difference signal and a compressed version of the difference signal are transmitted to one or more remote receivers. At the receiver the usual, unchanged, difference signal is used as a reference signal for controlling the expansion of the compressed difference signal so as to cause the amplitude of the companded difference to equal the level of the usual difference signal. Thus, the expander is adaptive to any compression characteristic that might be employed at the transmitter. Further, the availability of the usual uncompressed difference signal at the receiver enables the adaptive decoding of dynamic parameters of the received signal, such as frequency response and attack and recovery times, so that all of the parameters of the original signal can be restored automatically.

Abstract: A digital dynamic range converter of the forward control type for varying the dynamic range of a digital audio signal constituted by a sequence of audio signal samples. Each audio signal sample x(n) is multiplied by a control signal sample s(n) which is delivered by a digital control signal generator. This control signal generator has applied to it unipolar signal samples x(n) which are derived via a transmission channel from the audio signal samples x(n). In order to cause this dynamic range converter to respond rapidly to abrupt variations in the audio signal and to render it moreover universally usable, the control signal generator is provided with a digital peak-value detector which converts the sequence of unipolar signal samples x(n) into a sequence of peak-value samples x(n). The latter are applied to a digital non-linear amplitude transformation circuit which has an adjustable amplitude transmission characteristic curve determined by adjustment quantities R and a.

Abstract: Apparatus for processing speech in radioelectric transmitter/receiver equipment is adapted to transmitting and receiving speech. The apparatus comprises a compression circuit for compressing the dynamic range of the speech signal, said compression circuit being formed by at least one variable transmission attenuator for maintaining the level of speech modulation substantially constant throughout speech transmission. An expander re-establishes on reception the level of speech before it was compressed. An expander control device is responsive to the attenuation value applied by the transmission attenuator and transmitted over an auxiliary radioelectric frequency channel of the equipment. The compression circuit is an incremental compression circuit with a time anticipated action.

Abstract: A circuit that combines the functions of audio compression and voice detection comprises an amplifier in a negative-feedback configuration in which the feedback signal is the product of the output of the amplifier and a syllabic voltage derived from that output. The syllabic voltage is compared with a threshold level to provide an output that is a measure of the presence of a voice signal. In an alternate embodiment, the syllabic voltage is compared with the sum of a threshold level and a detected syllabic voltage to generate a signal that is a measure of the presence of voice. The syllabic detector may be either an averaging detector or a valley detector.

Abstract: An analog speech signal is sampled of a nominal rate of 6 kilohertz and digitized in a Mu-Law Encoder. The digital output of the Mu-Law Encoder is converted by a microprocessor performing table look-up to linearized pulse code modulation (PCM) samples nominally of eight bits per sample. Using a BSPCM (Block Scaled Pulse Code Modulation) method, in each block of nominally 246 eight-bit PCM samples (representing approximately 41 milliseconds), the maximum and minimum sample values are found and used to calculate a scale factor equal to the maximum sample value minus the minimum sample value, with the difference being then divided by a constant number nominally equaling 16. Then the BSPCM samples are generated from the PCM samples each as a corresponding one PCM sample minus the minimum PCM sample value, the difference being then divided by the scale factor. In effect, the bit rate is reduced by adjusting the step size to follow the local block dynamic range.

Abstract: A flat frequency response compansion noise reduction system employs both input signal and control signal preemphasis and deemphasis in its encoder and decoder networks respectively. The linear range of the frequency response curve of the input signal deemphasis is selected to approximate the frequency range within the audio spectrum at which the human ear is most sensitive, typically having a high frequency end of 3.617 kHz. The frequency response curve of the input signal preemphasis is a mirror image of the frequency response curve of the input signal deemphasis. The linear range of the frequency response curve of the control signal preemphasis is selected to provide an encoder output signal having a substantially flat response. The frequency response curve of the control signal deemphasis is a mirror image of the frequency response curve of the control signal preemphasis. The amount of preemphasis is maximized to the limits of the recording medium, typically ranging from 0 db to 20 db.

Abstract: A compression/expansion device is adapted to compress and expand gains of additive and subtractive signals at each level of at least two audio signals, characterized in that each audio signal or any one of the additive and subtractive signals is compressed at the compressing side and expanded at the expanding side depending on the level of the additive signal.

Abstract: An exemplary embodiment includes a plurality of parallel signal channels coupled with a signal input transducer, such as a microphone or induction coil. Each of the signal channels includes a respective bandpass filter for selection of a different frequency band, a controlled-gain amplifier, controlled by a volume control potentiometer, circuits for non-linear signal processing, and a bandpass filter for the reduction of distortion components caused by the non-linear processing circuits. A summing amplifier combines the signal components from all channels and is connected via an amplifier to an output signal transducer. Space requirements and power consumption are reduced in such a multi-channel processing arrangement by implementing all of the filters as sampled-data analog circuits. As a result hearing aids are provided which can be worn on the head, e.g. behind the ear.

Abstract: Apparatus for reducing unmasked quantizing noise modulation in adapting differential digital coding systems. In the digital encoder low frequency signals are boosted in the presence of dominating high frequency signals that are controlling the quantizing step size. The decoder has complementary cutting of low frequency signals. Optionally, unmasked high frequency noise modulation is reduced by variable pre- and de-emphasis.

Abstract: Circuit arrangements for cross-coupling series connected bi-linear compressors and expanders are disclosed including the coupling of signal path signal components in one circuit to a signal path in another circuit, the coupling of control circuit signal components in one circuit to a control circuit in another circuit and cross-coupling by way of employing a common control circuit for series connected devices.

Abstract: A peak limiter is described which employs the Hilbert transform. Effectively distinct processing occurs for low frequency and high frequency signals and harmonic distortion results only when the limiter is excited by high frequencies.

Abstract: In order to reduce the effect of modulation of the quantizing error (noise) by the signal in an adaptive digital audio system and to increase the dynamic range of the system, the adaptive analog to digital converter is preceded by a frequency dependent network that changes the shape of its characteristic in response to a control signal. The control signal is derived from the variable scaling factor in the adaptive converter. After transmission via a transmission channel or record/playback process, complementary operations are performed by a digital to analog converter followed by a further frequency dependent variable response network.

Abstract: In a first aspect of the invention, compressor and expander circuits are arranged in series, the dynamic actions of the circuits being substantially separated with respect to level. The changing gain portions of the characteristics are staggered among the series circuits such that the resulting overall characteristic has a maximum compression or expansion ratio substantially no greater than that of any single circuit while providing more compression or expansion than for any of the circuits individually. A second aspect, referred to as "spectral skewing", effects a reduction of the influence of signals in the high and/or low frequency extremes of a signal transmission system on the action of a compressor feeding the transmission channel. Consequently, a complementary expander fed by the channel is less likely to be controlled by signals at frequencies subject to transmission channel errors. A third aspect provides an anti-saturation effect.

Abstract: An audio loudness control system for processing a broad dynamic range of audio input signals (e.g. 70 to 100 dB) comprises a gain-controlled amplifier, a feed forward control signal generator having an audio signal input that develops a feed forward gain control signal having an amplitude representative of long-term input excursions of the audio signal above a predetermined loudness threshold, a feedback control signal generator having an input from the audio output of the amplifier that develops a feedback gain control signal having an amplitude representative of transient output signal excursions above the loudness threshold, and a selector gate that selects the gain control signal of instantaneously higher effective magnitude and applies the selected gain control signal to the gain control input of the amplifier.

Abstract: A signal transfer and processing system for use with a transmission line includes transmission line interface circuitry (30) and signal processing circuitry (100). The processing circuitry receives a signal to be processed, providing a processed signal for further use. An input bandpass filter (119, SW7) selectively limits bandwidth the input signal. A primary active frequency control (123) selectively controls the relative level of the signal provided from the primary bandpass filter means for selectively controlling the relative level of signal dynamics within different frequency bands for providing a frequency controlled signal, which is compressed by a compressor (127). A secondary active frequency control (135) selectively controls the relative level of the primarily compressed signal within different frequency bands to provide a frequency controlled primarily compressed signal which is further compressed by a secondary compressor (137).

Abstract: A speech processor having microprocessor control of the amplitude level of input speech signals. Input speech signals are applied to a digitally controlled level regulator, the output of which is converted into a digital speech signal for further speech processing. The peak level of the digital speech signals over a frame period is compared in the microprocessor with a preset optimum range. If the peak level falls outside the optimum range, control signals for the level regulator are adjusted in a direction to change the amplification/attenuation amount of the level regulator to bring the peak level within the optimum range.

Abstract: In a communications system, consonant high frequency sounds are enhanced: the greater the high frequency content relative to the low, the more such high frequency content is boosted.

Abstract: In an ADPCM system, improved detection of silence intervals in a speech signal is attained by detecting the level of the logarithm step-size signal (d.sub.n), which is representative of the energy of the speech samples. A speech pattern is converted into a sequence of adaptive digital codes. Intervals of silence in the pattern are detected and a digital code representative of each silence interval is generated. The adaptive digital codes and the silence interval codes are combined to form a digitally coded signal representative of the pattern. The conversion of the pattern to adaptive digital codes includes forming a signal corresponding to the adaptation step-size for each digital code. The silence interval detection includes producing first and second threshold signals.

Abstract: A noise reducing apparatus consists of a compression system and an expansion system. The compression system comprises a pre-emphasis circuit for performing a pre-emphasis operation with respect to an input signal, a first variable gain control circuit for giving a level compression characteristic to an output signal of the pre-emphasis circuit, to produce an output signal to a transmission path, a first control voltage producing circuit for dividing the output signal of the first variable gain control circuit into a plurality of bands, to produce a plurality of control voltages respectively given mutually different bands, a first weighting circuit for respectively and relatively weighting the plurality of control voltages obtained from the first control voltage producing circuit, and a first adding circuit for adding the plurality of control voltages obtained from the first weighting circuit, to obtain a first control voltage and apply this first control voltage to the first variable gain control circuit.

Abstract: A noise reduction circuit comprising first and second variable frequency amplifiers (3, 4; 12, 13) for respectively amplifying first and second audio signals at variable gains in response to a control signal, a frequency splitter (23-26; 42-45) for splitting each output signal of the first and second variable gain amplifiers into high and low frequency components, an envelope detector (27-30; 46-49) for detecting the envelopes of the high and low frequency components of each audio signal and generating therefrom first and second high frequency component envelopes and first and second low frequency component envelopes, a combining circuit (31, 32; 50, 51) for combining the first and second high frequency component envelopes to generate a combined high frequency output and combining the first and second low frequency component envelopes to generate a combined low frequency output, and means (33-35; 52-54) for integrating the combined high frequency output with a smaller time constant and integrating the combine