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G.711 Speech Coder DSP C Code

Description: ITU G.711 coding implements the digitisation process on telephone signals used within digital telephone exchanges so representing standard telephone quality speech. The sample rate is 8kHz with the signal bandlimited to the range 300Hz to 3.4kHz. The compression by Pulse Code Modulation (PCM) is to a data rate of 64kb/s. Each input linear sample is assigned an 8-bit PCM code depending on its amplitude. Two coding methods are implemented that are similar but not compatible: A-law, as used in European telephone networks, and µ-law, as used in American and Japanese telephony circuits. G.711 is also a standard for video conferencing audio, and is often used for speech storage. The coding process can pass data modem signals up to V.34 ie 33.6kb/s.
         The C code is suitable for any processor with an ANSI-compliant C compiler. It is designed especially for efficient operation on low-cost fixed-point DSP- and general-purpose micro-processors. All data memory is specified as 16-bit integer words. Multiplies are integer 16x16-bit with 32-bit products.
         In the Algotron implementation, encoder and decoder are operated as separate items. Each has an individual per-sample/PCM-code subroutine call. No permanent memory is used. A comprehensive user's guide is provided with the code.

Processor Load:

- #example figures from compiling for the TI TMS320C5000(C55x) DSP processor

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