ETSI Standard Vocoders
ETSI EFR-GSM
The algorithm implemented is the
ETSI Adaptive Multi-Rate (AMR) GSM recommendation, digital cellular telecommunications
system. The encoder compresses linear-PCM (Pulse Code Modulated) speech input
data, at a sample rate of 8kHz, to one of eight data rate modes 12 200, 10
200, 7 950, 7 400, 6 700, 5 900, 5 500 and 4 750 bps. There is also one mode
to handle non-speech frames. The data rate is run-time selectable by the user.
The AMR-GSM algorithm implements
silence compression techniques to reduce the transmitted bit rate during the
silent intervals of speech. Systems allowing discontinuous transmission (DTX)
are based on Voice Activity Detection (VAD) algorithms and Comfort Noise Generator
(CNG) algorithms that allows the insertion of Silence Insertion Descriptor
(SID) frames during the silence intervals. This also provides the additional
advantage of using lower processing loads and DSP bandwidth resource during
silence frames.
The AMR-GSM speech coding algorithm
is a member of a subset of the linear predictive coders (LPC) known as the
ACELP (Algebraic-Codebook-Excited Linear Predictive Coding) class of coders.
Integrated IS-641-A and EFR-GSM functionality is also available.
back to menu