Adaptive differential pulse-code modulation Adaptive
differential pulse-code modulation (ADPCM) is a variant of
differential pulse-code modulation (DPCM) that varies the size
of the quantization step, to allow further reduction of the
required bandwidth for a given signal-to-noise ratio. Typically,
the adaptation to signal statistics in ADPCM consists simply of
an adaptive scale factor before quantizing the difference in the
DPCM encoder.  In telephony In telephony, a standard audio
signal for a single phone call is encoded as 8000 analog samples
per second, of 8 bits each, giving a 64 kbit/s digital signal
known as DS0. The default signal compression encoding on a DS0
is either μ-law (mu-law) PCM (North America and Japan) or A-law
PCM (Europe and most of the rest of the world). These are
logarithmic compression systems where a 13 or 14 bit linear PCM
sample number is mapped into an 8 bit value. This system is
described by international standard G.711. Where circuit costs
are high and loss of voice quality is