Contains libraries and binaries for a GSM speech compressor. libgsm contains a standard implementation of the European GSM 06.10 provisional standard for full-rate speech transcoding, prI-ETS 300 036,
which uses RPE/LTP (residual pulse excitation/long term prediction) coding at 13 kbit/s.
GSM 06.10 compresses frames of 160 13-bit samples (8 kHz sampling rate, which is a frame rate of 50 Hz) into 260 bits. For compatibility with typical UNIX applications, our implementation turns frames of 160 16-bit linear samples into 33-byte frames (1650 Bytes/s). The quality of the algorithm is good enough for reliable speaker recognition. Even music often survives transcoding in recognizable form (given the bandwidth limitations of 8 kHz sampling rate).
The interfaces offered are a front-end modeled after compress(1) and a library API. Compression and decompression run faster than real-time on most SPARC stations. The implementation has been verified against the ETSI standard test patterns.