Abstract: A digital SSB modulator in which an analog signal such as a vocal signal is temporarily converted to a digital signal, which is then subjected to SSB modulation using digital phase shifters and digital orthogonal amplitude modulators, and the resulting signal is converted back to an analog modulated signal. A digital filter may be provided after each digital phase shifter for eliminating direct-current signal components. Another digital filter may be provided after each digital orthogonal amplitude modulator for eliminating carrier signal components.

Abstract: An AM demodulator of a digital signal processing type wherein an analog AM signal is converted to a digital AM signal, the digital AM signal is squared and a one sample-delayed version of the digital AM signal is squared, these squared signals are added, and the square root of the resulting sum of the squared signals is extracted as an AM demodulated signal. The demodulator comprises a detector for detecting the level of a sum signal representing the sum of the squared signals, an upward bit shifter for bit shifting upwardly the sum signal on the basis of the detection output from the level detector, a polynomial calculator for approximately extracting the square root of the sum signal, and a downward bit shifter for bit shifting downwardly the output signal from the polynomial calculator.

Abstract: A frequency converting apparatus including a sample circuit and a bandpass filter wherein an input analog signal is sampled at predetermined periods only for predetermined time intervals to produce or increase the harmonic components of the original analog signal, a desired frequency component is extracted through the bandpass filter from the harmonic components to thereby convert the original signal having a particular frequency band to a signal having a higher-frequency band.

Abstract: In stereo sound reproduction circuitry for use with a stereo signal source and stereo headphones, the improvement of dip filter means disposed between the stereo signal source and the stereo headphones, the dip filter means having a dip in the transmission characteristic thereof, the dip being in substantially the same frequency position as a dip which occurs in the sound pressure frequency response characteristic at the ear canal entrance when a sound source is disposed in front of a listener.