GB1473472A - Elimination of transients in processing segments of audio information - Google Patents

Abstract

1473472 Audio signal compressors WESTINGHOUSE ELECTRIC CORP 13 Jan 1975 [23 Jan 1974] 1272/75 Heading H4R In a system for time compression of an audio signal, e.g. so that it may be recorded in a manner similar to video signals, the signal is time divided into discrete segments, each coinprising a number of signal samples, with a number of the last signal samples of one speech segment being repeated as the first signal samples of the following segment, the repeated samples of a segment occupying a time greater than the time of duration of transients produced during processing. As described during a record mode input signals after passing through audio band pass filter 20 are sampled at 24 converted to digital form in a to d converter 26 and fed, via switch 28 in shift register store 30 at a sample rate of 14À8 kHz. After 495 new samples have been entered into the store 30, which has 512 storage locations, switch 28 is changed to a recirculate condition and the clock feed to the shift register is converted to 10À74 MHz so that the contents of the store are recirculated and also fed out at high speed via d to a converter 34 to be applied as a video signal to be recorded on disc D, which rotates at television frame frequency and is phase locked to a television line frequency signal applied to phase comparator 12. The video signal recorded comprises 495 new samples of the incoming audio signal together with 17 samples of the previously recorded segment. After the segment has been recorded the clock feed is restored to 14À8 kHz, switch 28 is restored to feed new samples into the store, and the 495 oldest samples in the store are replaced by fresh samples and the compression process repeated. The recording on the disc D is such that the 512 analog samples are recorded as an FM signal in a time of 47 ÁS with successive groups of samples recorded adjacent preceding samples, spaced such that they occur on reproduction at television line frequency with the drum rotation such that a television frame period occupies one rotation of the drum. On playback the system is reversed with the signals being read off the drum at high speed into store 30 and read from there, for reproduction, at low speed. A logic circuit, for generating the various clock frequencies, is described with reference to Fig. 2 (not shown).