GB1497394A - Recording and reproduction of audio signals - Google Patents

Abstract

1497394 Recording and playback EMI Ltd 17 Jan 1975 [22 Jan 1974] 02947/74 Heading G5R [Also in Division H4] In a system for recording multichannel audio information a first channel signal L frequency modulates a carrier which is recorded in a first recording channel while a second channel signal R is inverted at 4, and frequency modulates a carrier which is recorded in a second recording channel. On reproduction from the recording the channel signals are demodulated at 8 and 9, the second channel signal is inverted, at 10, to restore its initial phase and the two channel signals are separated by filters 14 to 17, into components above and below 200Hz. The low frequencies of the two channels are combined, at 18, in the ratio 0À5 to 0À5 and the combined signal added to each of the high frequency channel signals, at 19 and 20, to provide two output signals, each containing the respective high frequency portion and a common low frequency portion, in which low frequency rumble, introduced into the channel signals by the mechanics of the recording process, has been cancelled. The loss of information by combining the low frequency components is negligible since the low frequencies contain negligible directional information.