Editing NICAM (section)

=== NICAM transmission problems ===

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There are some latent issues involved with the processing of NICAM audio in the transmission chain.
* NICAM (unlike the Compact Disc standard) samples 14-bit audio at 32&nbsp;kHz.
* The upper frequency limit of a NICAM sound channel is 15&nbsp;kHz due to anti-aliasing filters at the encoder. 
* The original 14-bit PCM audio samples are companded digitally to 10 bits for transmission.
* NICAM audio samples are divided into blocks of 32. If all the samples in a block are quiet, such that the [[most significant bit]]s are all zeros, these bits can be discarded at no loss.
* On louder samples some of the [[least significant bit]]s are truncated, with the hope that they will be inaudible.
* A 3-bit control signal for each block records which bits were discarded.
* Digital companding (using a [[CCITT J.17]] pre-emphasis curve) ensures that the encoding and decoding algorithms can track perfectly.