Equivalent pulse code modulation noise

In telecommunication, equivalent pulse code modulation noise (PCM) is the amount of thermal noise power on a frequency-division multiplexed (FDM) or wire channel necessary to approximate the same judgment of speech quality created by quantizing noise in a PCM channel.

Note 1: The speech quality judgment is based on comparative tests.

Note 2: Generally, 33.5 dBrnC ±2.5 dB is considered the approximate equivalent PCM noise of a 7-bit PCM system.

Source: from Federal Standard 1037C and from MIL-STD-188