NHK developed the first mono PCM recorder with 30kHz/12bit converter and video tape recording at its research centre in 1967. The concept of converting PCM data into VTR-compatible (video magnetic tape) signals was maintained until the 1990s. In 1969 it was further developed to 2-channel/32kHz/13bit.
In 1969, NHK expanded the system’s capabilities to 2-channel stereo and 32 kHz 13-bit resolution. In January 1971, using NHK’s PCM recording system, engineers at Denon recorded the first commercial digital recordings.