Although data links are increasing in bandwidth and are becoming faster, speech communication is still the most dominant and common service in telecommunication networks. The fact that commercial and private usage of telephony in its various forms (especially wireless) continues to grow even a century after its first inception is obvious proof of its popularity as a form of communication. This popularity is expected to remain steady for the fore-seeable future. The traditional plain analogue system has served telephony systems remarkably well considering its technological simplicity. However, modern information technology requirements have introduced the need for a more robust and flexible alternative to the analogue systems. Although the encoding of speech other than straight conversion to an analogue signal has been studied and employed for decades, it is only in the last 20 to 30 years that it has really taken on significant prominence. This is a direct result of many factors, including the introduction of many new application areas.

The attractions of digitally-encoded speech are obvious. As speech is condensed to a binary sequence, all of the advantages offered by digital systems are available for exploitation. These include the ease of regeneration and signalling, flexibility, security, and integration into the evolving new wireless systems. Although digitally-encoded speech possesses many advantages over its analogue counterpart, it nevertheless requires extra ...

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