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The ITU-T G.729 Annex A with Annex B fixed-rate speech coder provides toll quality at very low bandwidth. G.729 compresses narrowband linear speech signals at a sample rate of 8kHz to 8kbps, using Conjugate-Structure, Algebraic Code-Excited Linear Prediction (CS-ACELP). The encoder extracts the parameters of the CELP coding model from 10-msec frames. G.729 Annex A is a less mathematically complex version of G.729. It requires roughly one half the cycles of G.729, yet is interoperable with it, with barely any loss of fidelity.
Annex B implements optional silence-compression techniques to reduce the transmitted bit rate during the silent periods of speech. Discontinuous transmission systems (DTX) use Voice Activity Detection (VAD) and Comfort Noise Generation (CNG). The coder uses occasional Silence Insertion Descriptor (SID) frames during silence. Silence Detection is optional and can be turned on and off on the fly. Executing G.729 Annex A with Annex B with Voice Activation Decision turned off will give exactly the same results as executing G.729 Annex A without Annex B.
G.729 Annex A with Annex B encoder is widely used in applications that require robust quality, including videoconferencing, internet, multimedia communications, satellite communications, and store/forward. G.729 Annex A with Annex B is the most commonly used speech coder of the G.729 family.
The G.729 Annex A with Annex B has been extremely optimized by DSP Wizard to execute on a Win32 PC or any other multipurpose processor and yet remain bit-exact to the ITU-T standard. DSP Wizard’s G.729 Annex A with Annex B will execute nine times faster than the source code published by ITU. On a typical PC with a 3.0GHz processor, encoding and decoding a channel of speech requires only 4% of the processor’s CPU cycles. So a user should be able to process 25 independent channels of speech. This should be fast enough for most real-time applications.
DSP Wizard’s G.729 Annex A with Annex B implementation was designed for low resource requirements without sacrificing quality. The speed is extremely fast compared to the published standard, yet it is still bit-exact to the ITU-T standard test suite. Furthermore, the code should be portable to any machine that supports the C language.