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The Sony PCM-501ES digital audio processor is a piece of equipment that offers digital sound recording and playback. It was released in 1984 and was sold as a semi-professional product, part of the PCM adaptor family of products. The cost was about 900 USD. It was by far the most popular of all the PCM adaptors.
The 501ES sound quality is set at 16-bit/44,1 kHz. 14-bit encoding is also possible in order to record media that is compatible with the similar PCM adaptor from Matsushita Technics. As with all LPCM “Adapters” standardized by the EIAJ, the 501 incorporated a single converter that was time–domain multiplexed between channels.
The 501ES has to be placed between a sound source and a video recorder. The use of a VHS videotape recorder, or a Betamax videotape recorder offers recording while using low cost media. V2000 consumer video from Philips and U-Matic professional video from Sony are compatible systems too. Dropouts problems occurs more often with VHS than with other video systems. Older/earlier VHS recorders tend to work better than later ones, since the "HQ" video noise reduction system found on later VHS machines conflicts with the PCM adapter's error correction/concealment techniques, leading to more frequent error correction or concealment failure.
The videorecorder does not have to be hifi-stereo. As stereo sound from the source is converted into PCM code in video form while recording, and converted back into stereo sound while playing. The videotape soundtrack is not used by the system and is left blank while recording.
In LP mode, a 5-hour VHS tape provides as much as 10 hours of non-stop mixed music program. That feature makes the 501ES a good choice for radio stations broadcasting during low audience hours.
In playback mode the sound quality is improved when using two 501ES along instead of just one. The video signal from the Videocassette recorder (VCR) goes into the video input of a first 501ES. With copy duplication on, the video signal is re-generated and goes into the video input of a second 501ES. Analog output of that second 501ES then brings a better sound quality than the one provided by the first 501ES alone.
Model 601ES later brought digital output, which offers an alternative for re-archiving legacy recordings.