GB1433411A - Time compression of audio signals - Google Patents

Abstract

1433411 Audio compression WESTING- HOUSE ELECTRIC CORP 26 March 1973 [7 April 1972] 14332/73 Heading H4R Audio signals are converted to video format by producing time-compressed segments of duration corresponding to the picture portion of a video line and inserting video sync. signals in the gaps between them. General.-The audio signals are read into a store, read-out faster and recorded with the sync. signals on a magnetic disc or tape. The system described uses a 525 line standard. Compression.-The audio input 101 is restricted 102 to 6 kHz, converted 103 to a sevenbit code and read-in to register 104 at 15750 Hz (i.e. 525 x 30) governed by the reference track on the disc. The track has 525 recorded pulses of which one is distinguishable via integrating and differentiating discriminator 111 to generate signals f 1 of one pulse every revolution (33 msec.) and f 2 to. 525 pulses per revolution. Operation of start circuit 110 and detection of an f 1 pulse produces a reset signal S for the dividers. When 526 f 2 pulses have been counted in divider 115 it opens gate 118 via delay 117 to read-out register 104 at 10 MHz from source 119. The D/A converted and 4 MHz filtered output occupies 53 Ásec., corresponding to a video picture portion, and is frequency modulated 107 on a carrier gated 108 for a line period of 64 Ásec. by divider 115. This cycle is repeated 252 times as determined by divider 122 to gradually build up half a track of recording after which generator 123 suppresses ten f 2 pulses to provide the 10-line vertical blanking interval. After the next 252 cycles divider 124 blocks gate 113 for an extra f 2 pulse making an 11-line blanking interval, and switching to the next track. A waveform generator 18 phase-locked 16 with disc rotation inserts the corresponding vertical blanking and sync. signals. Phase discontinuities between recorded FM bursts occur in horizontal sync. intervals and are not noticable. The recording is reproduced through an amplifier (22, Fig. 3, not shown) which inserts the horizontal blanking and sync. signals and possibly identification codes in line 525 before re-recording on a broadcast video tape recorder (24). Expansion.-The original audio signals are recovered by reproducing the disc through similar equipment (Fig. 5, not shown) having transposed A/D converters, demodulator and data rates with the waveform generator 18 replaced by a reference such as 60 Hz mains. Refinements.-Read-out during vertical blanking intervals loses audio data which may be replaced by the use of parallel registers alternately reading-in and reading-out (Figs. 10, 11, not shown). Display.-A disc carrying compressed audio interspersed, e.g. in alternate tracks with video signals is displayed by detecting a video code, temporarily storing (Fig. 13) and continuouslydisplaying the stored video on a monitor whilst the corresponding audio signals are expanded (216) and reproduced.