VS1103B datasheet(38/61 Pages) ETC2

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VLSI

Solution

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

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