ITU-T Standard Vocoders
G.726
The algorithm implemented is the
ITU-T G.726 recommendation, variable rate audio coder. The encoder compresses
narrowband audio data in A-law or mu-law linear-PCM (Pulse Code Modulated)
format, at a sample rate of 8kHz, to 16 000, 24 000, 32 000 and 40 000 bps.
G726 supersedes G721 and G.723, as the G.726 specification at 32 000 and 40
000 bps is identical to G.721 (32 000 bps only) and G.723 (32,000 and 40,000
bps).
The G.726 specification uses an
Adaptive Differential Pulse Code Modulation (ADPCM) algorithm. An important
feature is that the coding/decoding delay is essentially zero, as the algorithm
processes one sample at a time.
The main application of 24 000
and 16 000 bps channels is for overload channels carrying voice in Digital
Circuit Multiplication Equipment (DCME). The 40 000 bps channel is to carry
data modem signals in DCME, especially for modems operating at greater than
4 800 bps. G.726 is now also widely used for Voice over DSL applications.
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