Unlocking hi-fi treasure

摘要

Perhaps like many of us, I've used the lockdown as a way to finally get around to clearing out my garage and attic. There I found literally thousands of mainly VHS video cassettes, many storing music recordings from TV and radio stations. Lest we forget, during the '80s and '90s JVC's VHS (and Sony's Betamax) videocassette recorders were able to tape and play back very high quality analogue audio. Although the 1/2in tape moved slowly, the rapidly spinning helical-scan record/play heads gave high tape-to-head speed and an effective bandwidth of over 3MHz. Stereo audio was also recorded by the spinning heads. This was FM, like broadcast radio, with L/R channels on different frequency-modulated carriers, with depth multiplexing. Audio was recorded at a lower frequency than the video - deeper in the tape coating than the higher frequency video. The result was flat response between 20Hz-20kHz, a claimed 70dB S/N ratio and 90dB dynamic range. So VHS and Beta Hi-Fi ostensibly delivered CD quality without digits. FM radio stations linked with TV stations to broadcast simulcasts, and VCRs came with the option to record hi-fi radio without video. TV companies started using NICAM stereo to transmit music with high audio quality.