GSM

Description
The GSM codec or GSM 6.10 RPE-LTP (Regular-Pulse Excitation Long-Term Predictor) is the low-level speech compression algorithm used in the GSM mobile system. It produces telephone quality speech with a bitrate of 13 kbit/s.

Software

 * FFmpeg
 * SoX

Sample files

 * https://telparia.com/fileFormatSamples/audio/gsm/

Links

 * GSM 06.10 lossy speech compression
 * Free codec implementation in C