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.
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References in periodicals archive ?
[20] Perceptual Evaluation of Speech Quality (PESQ): An Objective Method for End-to-end Speech Quality Assessment of Narrowband Telephone Net-works and Speech Codecs, International Telecommunication Union Std.
Moreover, we compare performance of the proposed schemes with the wideband rate distortion bound, which represents the lower bound of performance of several standardized ADPCM speech codecs for wideband speech, including the G.722 standard [22] and its extensions, as shown in [21].
The text is unusual in providing a complete history of the development of the technology, followed by its detailed description of theory and practice, including an exhaustive discussion of all current standardized speech codecs. Transmission and coding are covered at length.
The modules GSM voice data, fax and SMS support provide access to a TCP/IP stack via AT commands, as well as support for HR, FR, EFR and AMR speech codecs. The modules have a 60-pin external functions connector and serial interface.