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.