Although this site is primary dedicated to audio recording technologies, it’s important to remember that many video recording technologies also record audio. The original Betamax system, which Sony introduced May 10, 1975, had a single, monophonic sound track, recorded alongside the video and sync tracks. While stereo sound had long since captured the commercial record and tape markets and was becoming universal in FM broadcasting, TV was still mono. Based on advertisements and other sources, Sony seemed to believe that consumers would be recording content off-the-air (although they later also pushed home videotape recorders as sources of content). In 1983, Sony introduced its Beta Hi-Fi models, which recorded in stereo using audio heads mounted on the video head drum and recording frequency modulated audio instead of the original linear, audio-frequency recording track. Sony would later introduce a pulse code modulated (PCM) audio recording accessory for the Betamax machine, aimed at professional or semi-professional users. This constituted one of the first commercially available digital audio recorders. The Wikipedia article on Betamax technology has some detail on the many other changes in Betamax audio over the years.