{{short description|Speech codec by Qualcomm}} {{inline|date=July 2009}} {{Infobox file format | name = Qualcomm PureVoice | icon = | logo = | extension = .qcp | mime = audio/qcelp | type code = | uniform type = | magic = | owner = [[Qualcomm]] | type = [[Lossy compression|Lossy]] [[Audio file format|audio]] | container for = | contained by = | extended from = | extended to = | standard = | released = {{start date and age|1994|df=y}} | latest_release_version = TIA IS-733 | latest_release_date = {{start date and age|1999|12|df=y}} | open = Yes | free = No }} '''Qualcomm code-excited linear prediction''' ('''QCELP'''), also known as '''Qualcomm PureVoice''', is a [[speech codec]] developed in 1994 by [[Qualcomm]] to increase the speech quality of the [[IS-96A]] codec earlier used in [[code-division multiple access|CDMA]] networks. It was later replaced with [[Enhanced Variable Rate Codec|EVRC]] to achieve better speech quality with fewer bits. The two versions, ''QCELP8'' and ''QCELP13'', operate at 8 and 13 [[kilobits per second]] (Kbit/s) respectively.
In [[Code-division multiple access|CDMA]] systems, a QCELP [[vocoder]] 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-bit [[Quantization (signal processing)|quantization]] 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 by [[Line coding|coding]] 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.
==References== * https://web.archive.org/web/20130129041829/http://www.rfdh.com/ez/system/db/lib_jnl/upload/2489/[CSD9904]_QCELP_Vocoders_in_CDMA_Systems_Design.pdf * [https://www.rarewares.org/rrw/purevoice.php Archived PureVoice encoder and player downloads]
{{Compression formats}} {{Compression Software Implementations}}
{{DEFAULTSORT:Qcelp}} [[Category:Speech codecs]] [[Category:Qualcomm|Code-excited linear prediction]]