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VS1103b Datasheet

OPERATION

7.4

ADPCM Recording

This chapter explains how to create RIFF/WAV ﬁle with IMA ADPCM format. This is a widely

supported 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: 1.04, 2018-03-16

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