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.