Abstract: A voice codec apparatus for predictive coding is disclosed, in which an automatic gain control circuit controls the gain for decoding by the use of a maximum prediction value generated at the time of coding. The accurate gain control of the output signal is thus made possible at the time of decoding.

Abstract: A signal discrimination circuit is provided with: a prediction circuit for releasing a prediction signal that is formed by making a linear prediction based on a previous input signal; a differential operation circuit for calculating the difference between the input signal and the prediction signal so as to release a predicted remainder; and a decision circuit for determining whether or not the degree of the variation of the predicted remainder from the zero level is maintained within a predetermined range. Therefore, even if a sound signal having a time-wise correlation and white noise having no time-wise correlation possess wide frequency components respectively, both of the signals are discriminated by the decision circuit based on the difference in the correlation. Thus, the signal discrimination circuit ensures an accurate discrimination between a control signal for a facsimile containing white noise and a sound signal.

Abstract: In a data communication system, a modem for recording and reproducing audio tone data in addition to picture data includes an A/D converter, a D/A converter, and a digital modem section for demodulating the digital data outputted from the A/D converter and for modulating the digital demodulated data to be transmitted to the D/A converter. The system further includes a coding-decoding section for coding the digital data outputted from the A/D converter and for decoding the digital coded data to be transmitted to the D/A converter. The A/D and D/A converters are used in common for both the digital modem section and the coding-decoding section.

Abstract: A DTMF receiver for a push-button telephone, a facsimile apparatus or the like is disclosed. The DTMF receiver comprises frequency shift delay detection units for lower and higher groups of frequencies. Each of said frequency shift delay detection units comprises: a circuit for generating a first signal and second signal having a frequency obtained by subtracting the reference carrier frequency from the frequency of the corresponding frequency group, the signal having a phase difference of .pi./2 with respect to said first signal; another circuit for generating a third signal and fourth signal which are different in phase from the first and second signals, respectively; a vector calculation circuit in which the first and second signals are supplied to one input port, and the third and fourth signals to the other input port; and a detection circuit for detecting a phase difference between the outputs of the vector calculation circuit.

Abstract: A QAM demodulator having an adaptive automatic equalizer includes a transversal filter of a band-pass filter type, a reference carrier generator for generating a complex reference carrier, an error detector for obtaining complex error data, and a gain tap coefficient adjusting unit for adjusting the complex gain tap coefficients using the complex error data and the complex reference carrier data. The gain tap coefficient adjusting unit includes first complex multipliers for multiplying the complex data of the reference carrier outputted from the reference carrier generator by the input data, second complex multiplier for multiplying a predetermined coefficient by the complex error data outputted from the error detector, third complex multipliers for multiplying the output data of the first complex multipliers respectively by the output data of the second complex multiplier, thereby obtaining the complex quantity for adjusting the complex gain tap coefficients for the automatic equalizer.

Abstract: A quadrature amplitude modulation wave demodulator which includes a fixed equalizer having a first band-pass filter applied with a quadrature amplitude modulation wave reception signal for outputting an in-phase component with respect to a carrier wave for the reception signal, and a second band-pass filter applied with the reception signal for outputting a quadrature component with respect to the carrier wave for the reception signal. There is provided a vector multiplication section for performing vector multiplication between one vector having outputs of the first and second band-pass filters as two components, and another vector having two reference carrier waves in quadrature to each other as two components.