Circuit for time compression and expansion of audio signals

Abstract

A time compression or expansion circuit for audio signals comprises an analog to digital converter (12), a random access memory (17), a latch circuit (18), a digital to analog converter (19), a clock pulse generator (13), a counter circuit (14), a data selector (16), and a timing controller (13). The timing controller (15) is supplied with a clock pulse from the clock pulse generator (13) and a timing signal from the counter circuit (18), and produces a series of writing-in pulses and a series of strobe pulses which exist alternately and have a common frequency regardless of the mode of compression or expansion or rate thereof. The analog to digital converter (12) converts an input audio signal (11) to a digital signal in response to a writing-in and reading-out switching pulse from the counter circuit (18). The random access memory (17) writes the signal from the analog to digital converter (12) in response to the writing-in pulse fed from the timing controller (15), into an address thereof designated by an address datum for writing-in, and reading a signal out of an address thereof designated by an address datum for reading-out in response to the strobe pulse of the common frequency in such a way that the written address of the memory is read multiple times or skipped being read according to the mode and rate. The latch circuit (18) holds the signal read out from the random access memory (17) in response to the strobe pulse from the timing controller (15).