[3] NICAM was originally intended to provide broadcasters with six high-quality audio channels within a total bandwidth of 2048 kbit/s.
Several similar systems had been developed in various countries, and in about 1977/78 the BBC Research Department conducted listening tests to evaluate them.
The candidates were: It was found that NICAM-2 provided the best sound quality, but reduced programme-modulated noise to an unnecessarily low level at the expense of bit rate.
This means that the FM or AM regular mono sound carrier is left alone for reception by monaural receivers.
This latter mode could be used to transmit audio in different languages, in a similar manner to that used for in-flight movies on international flights.
In this mode, the user can select which soundtrack to listen to when watching the content by operating a "sound-select" control on the receiver.
Making the NICAM bitstream look more like white noise is important because this reduces signal patterning on adjacent TV channels.
NICAM sampling more closely resembles Adaptive Differential Pulse Code Modulation, or A-law companding with an extended, rapidly modifiable dynamic range.
Many VCRs later included high quality stereo audio recording as an additional feature, in which the incoming high quality stereo audio source (typically FM radio or NICAM TV) was frequency modulated and then recorded, in addition to the usual audio and video VCR tracks, using the same high-bandwidth helical scanning technique used for the video signal.