SARA-G3 series - System Integration Manual
UBX-13000995 - R06 Objective Specification System description
Page 71 of 218
The circular buffer is a 3000 word buffer to store and mix the voice-band samples from Midi synthesizer.
The buffer has a circular structure, so that when the write pointer reaches the end of the buffer, it is
wrapped to the begin address of the buffer.
Two different sample-based sample rate converters are used: an interpolator, required to convert the
sample-based voice-band processing sampling rate of 8 kHz to the analog audio front-end output rate of
47.6 kHz; a decimator, required to convert the circular buffer sampling rate of 47.6 kHz to the I2Sx TX
or the uplink path sample rate of 8 kHz.
1.10.3.2 Audio codecs
The following speech codecs are supported by firmware on the DSP :
GSM Half Rate (TCH/HS)
GSM Full Rate (TCH/FS)
GSM Enhanced Full Rate (TCH/EFR)
3GPP Adaptive Multi Rate (AMR) (TCH/AFS+TCH/AHS)
o In AMR Full Rate (AFS) the Active CODEC Set is selected from an overall set of 8 data
rates: 12.2 – 10.2 – 7.95 – 7.40 – 6.70 – 5.90 – 5.15 – 4.75 kb/s
o In AMR Half Rate (AHS) the overall set comprises 6 different data rates:
7.95 – 7.40 – 6.70 – 5.90 – 5.15 – 4.75 kb/s
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