Abstract: A characteristic control system for a digital equalizer comprises a digital equalizer constructed from a digital filter, for directly giving a desired equalizing characteristic with respect to a digital pulse-modulated signal, and a control part for changing the equalizing characteristic of the digital equalizer from a first arbitrary characteristic to a second arbitrary characteristic so that one or a plurality of intermediate equalizing characteristic is obtained before reaching the desired second arbitrary characteristic.

Abstract: A variable speed reproduction system includes a memory in which analog signal is stored as sampled digital data. A variable frequency digital low-pass filter is receptive of the data read out of the memory. A counter provides a binary representation of a count value of time base clock pulses to a comparator for detecting a coincidence with a variable speed setting of a variable resistor. The output of the comparator resets the counter and is used as a source of reading the data out of the memory. The cut-off frequency of the digital filter is controlled in response to the setting of the resistor so that the high frequency component of the analog equivalent of the input digital data which is higher than one-half of the data reading frequency is eliminated to prevent foldover distortion noise which might occur as a result of the difference between the recording and reproducing speeds.

Abstract: A compressing system for digital modulated signals comprises an analog-to-digital converter for obtaining a digital modulated signal by digitally modulating an analog signal; a first variable gain circuit provided at the output side of the analog-to-digital converter; and a first gain control circuit for equivalently performing level-compression of the analog conversion level of the input digital modulated signal of the first gain control circuit within a predetermined level range by use of a first control signal and the first variable gain circuit. The first gain control circuit comprises an expected signal generating circuit having an analog conversion level z.sub.n which satisfies the equation ##EQU1## (N is an arbitrary natural number, and a.sub.O through a.sub.N are zero or an arbitrary number) where y.sub.

Abstract: A circuit arrangement of a digital filter comprises an A/D converter supplied with an input analog signal and producing as output a pulse-modulated digital signal, a digital filter for subjecting the digital signal from the A/D converter to a digital operation processing of finite word length, a D/A converter supplied with the resulting output digital signal of the digital filter and converting the same into an analog signal thereby to generate an output analog signal, an input detector for detecting the state wherein there is substantially no input analog signal and responsively producing as output a detection signal, an integrator for integrating the output of the D/A converter, a switching circuit for operating in response to the output detection signal of the input detector to pass the resulting output signal of the integrator, a reference voltage source, and an adder for adding the signal thus passed by the switching circuit and a reference voltage from the reference voltage source and feeding back and i

Abstract: A binaural signal processing circuit comprising a first system for imparting an input signal with a transfer characteristic equal to the transfer characteristic hL(t; .theta., r) from a sound source to the left ear of a listener, where .theta. represents an angle between the front direction of the listener and the sound source, and r represents a distance between the sound source and the listener, a second system for imparting the input signal with a transfer characteristic equal to the transfer characteristic hR(t; .theta., r) from the sound source to the right ear of the listener, a system for variably controlling the transfer functions of the first and second transfer function imparting systems, and a further system for deriving binaural signals from the first and second transfer function imparting systems.

Abstract: A multichannel record disc reproducing apparatus comprises a first phase locked loop circuit including a phase comparator and a voltage controlled oscillator for demodulating an angle-modulated wave signal. The modulated signal is separated from a composite signal picked up from a multichannel record disc on which a multiplexed direct wave signal and an angle-modulated wave signal are recorded. The output of the first phase locked loop is a demodulated signal. A second phase locked loop circuit includes a phase comparator and a voltage controlled oscillator, supplied with the separated angle-modulated wave signal and having a lock range of a width which covers and is wider than the maximum lock range width of the first phase locked loop circuit. A synchronous detector compares the phases of the angle-modulated wave signal and the output signal of voltage controlled oscillator of the second phase locked loop.

Abstract: A multichannel record disc reproducing apparatus has a pickup cartridge for picking up signals from a multichannel record disc. A multiplexed signal was recorded on the disc by first multiplexing direct wave signals and angle-modulated wave signals which are recorded on opposite groove walls. Filters separate the picked up multiplexed signal into the direct wave signal and the angle-modulated wave signal. A demodulates circuit for demodulating the angle-modulated wave signal, thus separated. A matrix circuit separates the signals to obtain a plurality of separate channels from the direct wave signals and the demodulated signals. A circuit in a stage preceding the demodulator removes substantially all components of the higher harmonics at the carrier wave center frequency, which carrier was used for angle-modulating the original signal.

Abstract: A multichannel record disc reproducing system comprises a circuit for demodulating an angle-modulated wave picked up from a multichannel record disc. A circuit detects abnormal phenomena of the angle-modulated wave, whereupon an expansion circuit accomplishes a variable control operation. A middle frequency band and/or a high frequency band component of the demodulated signal is attenuated in accordance with the level thereof. A circuit is operated in response to the output of the detection circuit to stop a variable expansion control operation of the expansion circuit and imparts a specific attenuation characteristic to a signal passing through the expansion circuit.

Abstract: A combined matrix and equalizer circuit comprises a matrix circuit for operating with gains on a plurality of input signals. A feedback loop feeds back from a point between output terminals of the matrix circuit and a specific one of the input terminals of the same circuit. The feedback loop causes a signal entering a specific input terminal to have a specific equalizing frequency characteristic.

Abstract: A composite filter circuit comprises a first series resonant circuit connected to a single common resistor, resonating at a first frequency, and exhibiting a low-pass filtering characteristic. A parallel resonant circuit includes one circuit element of the first series resonant circuit and resonates at a second frequency. A second series resonant circuit is connected to the single common resistor, resonating at the second frequency, and exhibiting a highpass filtering characteristic. The first series resonant circuit and the parallel resonant circuit constitute a low-pass filter circuit section. This low-pass filtering characteristic results from the total effects of the low-pass filtering characteristic of the first series resonant circuit, a dip characteristic of the parallel resonant circuit, and, in addition, a decreasing characteristic at the second frequency, due to the second series resonant circuit.

Abstract: A multichannel record disc reproducing system and apparatus comprises a phase-locked loop for demodulating an angle-modulated wave signal in a multiplexed signal picked up from a multichannel record disc. A synchronous detector compares the phases of the angle-modulated wave signal and an output signal of a voltage-controlled oscillator in the phase-locked loop. The detector produces an output signal when there is a noise component in the angle-modulated wave signal. A circuit, controlled by the output of the synchronous detector, provides a demodulated output signal having at least one attenuated frequency band, in which a noise component is greatly reduced.

Abstract: A system for demodulating angle modulated waves comprises a phase locked loop including a phase comparator and a voltage controlled oscillator. An attenuation means is inserted into the phase locked loop. This attenuation means does not affect the DC component of an input angle modulated wave, but does cause an attenuation with respect to an AC component, to cause a decrease in the loop gain. The phase locked loop has a DC lock range exhibiting a relatively wide lock range width even when the input level is relatively low and an AC lock range produced by the attenuation circuit and exhibiting a relatively narrow lock range width when the input level is relatively low. The attenuation means detects an abnormality in the angle modulated wave, the harmonics component of the direct wave, and the like. A variable attenuation circuit controlled by the output of the detecting means is varied in its attenuation quantity.

Abstract: A limiting amplifier comprises a first differential amplifier having a transistor to which an input signal is applied and a transistor to which a constant voltage is applied. A second differential amplifier amplifies the output of the first differential amplifier. A DC component of the output of the second differential amplifier is applied as a negative feedback to the input side of the first differential amplifier. A limiting circuit is connected between a point which is connected to the output side of the second differential amplifier and a terminal for supplying constant voltage. The resulting differential amplifier is especially well suited for incorporation in a monolithic circuit.