Qualcomm code-excited linear prediction

{{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 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 CDMA networks. It was later replaced with 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 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 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 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.