VLSI
Solution
y
VS1103b
VS1103B
7. OPERATION
7.4 ADPCM Recording
This chapter explains how to create RIFF/WAV file with IMA ADPCM format. This is a widely sup-
ported ADPCM format and many PC audio playback programs can play it.
IMA ADPCM recording gives roughly a compression ratio of 4:1 compared to linear, 16-bit audio. This
makes it possible to record approx. 8 kHz audio at approx. 32.44 kbit/s or 44.1 kHz audio at 178.85
kbit/s.
7.4.1 Activating ADPCM Recording
IMA ADPCM recording mode is activated by setting bit SM ADPCM in SCI MODE. Before activating
ADPCM recording, user must see to it that SCI ADPCMRECCTL has been properly set.
7.4.2 Reading IMA ADPCM Data
After IMA ADPCM recording has been activated, results can be read through registers SCI IN0 and
SCI IN1.
The IMA ADPCM sample buffer size is 512 16-bit words, or 1 KiB. If the data is not read fast enough,
the buffer overflows and returns to empty state.
Each IMA ADPCM block consists of 128 words, i.e. 256 bytes (or 505 mono audio samples). If you
wish to interrupt reading data and possibly continue later, please stop at a 128-word boundary. This way
whole blocks are skipped and the encoded stream stays valid.
Note: if SCI IN1[15:8] ≥ 60 (i.e. there are more than 60 × 8 = 480 words waiting), wait for the buffer
to overflow and clear before reading samples to avoid buffer aliasing.
Version 1.01, 2007-09-03
38
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