The process of altering the form of a signal, such as from analog to digital. Or, the coding may be used to allow a transformation of the signal not possible in its original form such as in noise reduction. Or, coding may be used to take advantage of effects inherent in the coding process itself, such as in PCM which allows recording and playback with low noise. The complementary stage to coding is decoding, a process which attempts to reconstruct the original signal, i.e., from digital back to analog for use with loudspeakers. See codec.