Abstract: An audio compressor amplifier including an operational amplifier with compressor means connected from the output to the input for compressing signals at the output to a predetermined constant level in a predetermined attack time and including a plurality of diodes connected to reduce the series resistance in the compressor means for decreasing the attack time when the output signal exceeds the predetermined constant level by a predetermined amount, and a gain control feedback resistor connected from the output to the input of the operational amplifier and including a second resistor and a plurality of diodes connected in parallel therewith to reduce the gain of the operational amplifier and provide peak limiting action when a signal at the output exceeds a predetermined value in excess of the predetermined constant level.

Abstract: The invention concerns a dynamic range compressor type encoder or expander type decoder, in which a main signal component in a main path is boosted or bucked by a further signal component derived from a point in the main path by a further path having the characteristics of so restricting the further signal component that the boosting or bucking action is only appreciable below a low level threshold. In the present invention the further signal component is a difference signal formed between a direct signal derived from a point in the main path and a delayed version of either the same signal or of another signal derived from another point in the main path. At the frequency equal to the reciprocal of the delay, and at harmonics of this frequency, the direct and delayed signals cancel. The compressor or expander action, and hence noise reduction action, takes place only at intervening frequencies.

Abstract: This invention provides two dramatic improvements in the state of the art of side scan sonar systems and the like, bringing out the fine details of the sonar signals to enhance the texture of the sonar charts and to improve the quality and interpretability of the sonar records, while additionally bringing the sonar signals into the dynamic range of the recording medium in such a way that the tuning of the sonar instrument is greatly simplified and, in many situations, may be run continuously with no operator's adjustment of the instrument controls. These ends are attained through a novel compressed-signal absolute value smoothing and derivative processing, with dynamic range matching to the recording medium.

Abstract: A digital speech compression system uses a predictive feedback loop. The digital speech signals are compressed within the feedback loop for reducing the transmitter bandwidth. The system comprises a first adder into which the digital signal is fed followed by a quantizer and a compression logic. The predictive loop includes a second adder coupled to the compression logic and followed by a digital predictive filter. The output of the filter is impressed in a negative sense on the first adder and in a positive sense on the second adder. Specifically, the quantizer and compression logic may consist of a two-valued limiter followed by a compressor and a converter in the feedback loop or alternatively the limiter may be followed by a converter while the compressor is disposed outside the feedback loop to provide sample by sample compression.

Abstract: A signal processing system for providing compressor and expander operation which system includes a main, or straight through, signal path and a further signal path in parallel therewith. The further path derives its input from the input to the main path or from some later point in the signal path. The output of the further signal path is combined additively with that of the main path for compressor operation and subtractively for expander operation, such further signal path output being appropriately limited so that it can only make a noticeable contribution to the resultant signal level at low input signal levels. True complementarity is attainable by the use of a compressor and expander together to provide an overall noise reduction action without introducing defects into the signal being processed.

Abstract: In a circuit for the automatic dynamic compression or expansion of a signal between its input and its output, the circuit presenting a useful signal path connected between its input and its output and containing a setting member which is electronically controllable for varying the transmission factor between the circuit input and output, the circuit also presenting a branch path connected at one point to the useful signal path and containing a control voltage generator for generating, from the signal in the useful signal path, a control voltage applied to control the setting member, there is also provided a second setting member connected in the branch path and arranged to be electronically controllable for varying the transmission factor exhibited by the branch path, and means connecting the output of the control voltage generator to the second setting member for effecting a counterregulation of the transmission factor of the branch path, relative to the transmission factor variation imparted to the useful s

Abstract: A compressor or expander circuit is constructed by connecting a plurality of impedance networks in series across input terminals, at least one network being frequency selective. Output terminals are connected across one or more of the networks. The frequency selective network varies its parameters in response to the level of components within a restricted frequency band determined by this network so as to narrow the band when the level of such components increases. This includes such components from the restricted band and thereby from the compression or expansion action.

Abstract: The compressor part of a compander uses a differential amplifier to receive voice signals. Diode attenuator circuits are connected to the differential amplifier output and attenuate the differential amplifier output signals as a function of a rectified signal derived from the compressor output. The expander part of the compander also uses a differential amplifier to receive voice signals. The differential amplifier is interconnected by a diode attenuator circuit which varies the gain of the differential amplifier as a function of a rectified signal derived from the expander input. The compander thus requires no inductors and uses components which are relatively small and compact.

Abstract: A broad-band signal transmitting device including a signal transmitting transformer of the primary to secondary turn ratio 1 : N, comprising a first circuit for expanding the transmission band to low frequencies by decreasing the impedance as well as by decreasing the gain for the signal component in the primary circuit of the transmission transformer, a second circuit connected with the output side of the transmission transformer having an impedance larger than N.sup.2 times of the impedance of the primary side and smaller than the impedance exhibited by the stray capacitance of the secondary side at the upper limit of the transmission band, an amplifier for recovering the gain drop in the first circuit, and a low frequency compensating circuit for compensating the lack of low frequency transmission characteristic due to the transmission transformer.

Abstract: Amplitude samples of voice signals to be transmitted by pulse-code modulation are compared with a quasi-exponential reference voltage generated during each sampling interval while a binary counter receives a train of isochronous clock pulses, the reading of the counter at the instant of a match being stored in a memory for subsequent insertion into a message frame. Positive and negative signals are distinguished by a sign bit preceding the amplitude code; in one embodiment the reference voltage is sequentially generated with opposite polarities in successive halves of a sampling interval, the counter having an additional stage to generate the sign bit. Decoding at the receiving end is achieved with the aid of another binary counter whose output is compared with the amplitude code and, in the event of a match, causes the instantaneous value of a similar reference voltage to be sampled and stored for subsequent integration.

Abstract: An electronic tour guide system including means for suppressing objectionable crosstalk and noise is described. Crosstalk suppression is achieved by means of a comprssor in the transmitter and an expander in the receiver. Objectionable noise between loops is eliminated by means of a squelch circuit which reduces power drain whenever the received signal is below a certain threshold. The transmitter and receiver are designed to handle a plurality of information signals simultaneously. For example, a listener can select one of several different languages broadcast within an antenna loop. The transmitting loop antenna is matched in impedance to the output of the channel means in the transmitter so that maximum power transfer is obtained. Each receiver is further equipped with a gravity operated mercury switch which turns off power to the receiver when the receiver chasis is inverted.

Abstract: Compressors and expanders for effecting dynamic range modification are constructed by connecting reactive networks in series for voltage dividing action or in parallel for current dividing action. The output signal is derived from the voltage across or current through one of the networks which includes a series or parallel variable resistance. The variable resistance is controlled in dependence upon the voltage thereacross in the sense required to achieve compression or expansion, as the case may be. The resistance change shifts a turnover frequency of the circuit so as to exclude large amplitude components from the amplitude increase or reduction which is applied to low level components within a restricted frequency band to create the compressor or expander action.