Full Rate or FR or GSM-FR was the first digital speech coding standard used in GSM digital mobile phone system. The bit rate of the codec is 13 kbit/s. The quality of the coded speech is quite poor in modern standards, but at the time of development (early 1990s) it was a good compromise between computational complexity and quality. The codec is still widely used in networks around the world. Gradually FR will be replaced by Enhanced Full Rate (EFR) and Adaptive Multi-Rate (AMR) standards, which provide much higher speech quality with lower bit rate.
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Technology
GSM-FR is specified in ETSI 06.10 and is based on RPE-LTP (Regular Pulse Excitation - Long Term Prediction) speech coding paradigm. Like many other speech codecs, linear prediction is used in the synthesis filter. However, unlike most modern speech codecs, the order of the linear prediction is only 8. In modern narrowband speech codecs the order is usually 10 and in wideband speech codecs the order is usually 16.
Implementations
The free libgsm codec can encode and decode GSM Full Rate audio.
