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| Qualcomm PureVoice | |
|---|---|
| Filename extension | .qcp |
| Internet media type | audio/qcelp |
| Developed by | Qualcomm |
| Initial release | 1994; 31 years ago (1994) |
| Latest release | TIA IS-733 December 1999; 25 years ago (1999-12) |
| Type of format | Lossyaudio |
| Open format? | Yes |
| Free format? | No |
Qualcomm code-excited linear prediction (QCELP), also known asQualcomm PureVoice, is aspeech codec developed in 1994 byQualcomm to increase the speech quality of theIS-96A codec earlier used inCDMA networks. It was later replaced withEVRC to achieve better speech quality with fewer bits. The two versions,QCELP8 andQCELP13, operate at 8 and 13kilobits per second (Kbit/s) respectively.
InCDMA systems, a QCELPvocoder converts a sound signal into a signal transmissible within a circuit. In wired systems, voice signals are generally sampled at 8 kHz (that is, 8,000 sample values per second) and then encoded by 8-bitquantization for each sample value. Such a system transmits at 64 kbit/s, an expensive rate in a wireless system. A QCELP vocoder with variable rates can reduce the rate enough to fit a wireless system bycoding the information more efficiently. In particular, it can change its own coding rates based on the speaker's volume or pitch; a louder or higher-pitched voice requires a higher rate.