speech codec


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speech codec

Also called a "voice codec" or "vocoder," it is a hardware circuit that converts the spoken word into digital code and vice versa. It comprises the A/D and D/A conversion and compression technique (see G. standards). If music is encoded with a speech codec, it will not sound as good when decoded at the other end.

Specialized for Voice
A speech codec is an audio codec designed for human voice. By analyzing vocal tract sounds, a recipe for rebuilding the sound at the other end is sent rather than the soundwaves themselves. The speech codec is able to achieve a much higher compression ratio, which results in a smaller amount of digital data for transmission. When telephones were first digitized in the early 1960s, they generated digital streams of 64 Kbps (see PCM). Since then, speech codecs have reduced voice to as little as 5 Kbps and less. See audio codec, sampling, codec examples and codec.
References in periodicals archive ?
PSQM: Perceptual Speech Quality Measurement predicts subjective quality of speech codecs.
PAMS predicts overall subjective listening quality, while PSQM predicts subjective quality of speech codecs.
Speech codecs do not deliver other signals clearly, such as ambience sounds, music and background noise.
On 4th November CSR's Gary Spittle, Jacek Spiewla, Walter Kargus, Walter Zuluaga, and Xuejing Sun will co-present a paper on 'The objective evaluation of Wideband Speech codecs for Bluetooth voice communication'.
It supports a wide range of ITU-T narrow band and wide band speech codecs, and incorporates highly optimized echo canceller and noise canceller.
Audio and Voice Compression for Wireless and Wireline Communications, Second Edition is divided into four parts with Part I covering the basics, while Part II outlines the design of analysis-by-synthesis coding, including a 100-page chapter on virtually all existing standardised speech codecs.