Voice Coding

Whether based on CDMA or TDMA, all digital systems need to encode the analog waveforms of speech into a bitstream. The program used for this is called a codec (coder/decoder), often embedded within a special chip called a DSP (Digital Signal Processor). Many different codecs are used in cellphones, and new ones are developed each year. The aim is to produce the lowest possible bit rate while maintaining acceptable sound quality. Because computing power is increasing continuously, newer phones and networks are capable of using more advanced compression technology. Some popular codecs are listed in Table 3.2, together with their main uses.

The standard by which voice codecs are judged is the G.711 system, used in the PSTN (Public ...

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