VS1033 Datasheet, PDF(43/70 Page) List of Unclassifed Manufacturers

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VS1033 Datasheet, PDF (43/70 Pages) List of Unclassifed Manufacturers – MP3/AAC/WMA/MIDI AUDIO CODEC

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VLSI

Solution y

VS1033a PRELIMINARY

VS1033A

9. OPERATION

9.4.4 Playing ADPCM Data

In order to play back your IMA ADPCM recordings, you have to have a ï¬le with a header as described

in Chapter 9.4.3. If this is the case, all you need to do is to provide the ADPCM ï¬le through SDI as you

would with any audio ï¬le.

9.4.5 Sample Rate Considerations

VS10xx chips that support IMA ADPCM playback are capable of playing back ADPCM ï¬les with

any sample rate. However, some other programs may expect IMA ADPCM ï¬les to have some exact

sample rates, like 8000 or 11025 Hz. Also, some programs or systems do not support sample rates below

8000 Hz.

However, if you donât have an appropriate clock, you may not be able to get an exact 8 kHz sample rate.

If you have a 12 MHz clock, the closest sample rate you can get with 2.0 Ã 12 MHz and d = 12 is

fs = 7812.5Hz. Because the frequency error is only 2.4%, it may be best to set fs = 8000Hz to the

header if the same ï¬le is also to be played back with an PC. This causes the sample to be played back a

little faster (one minute is played in 59 seconds).

Note, however, that unless absolutely necessary, sample rates should not be tweaked in the way described

here.

If you want better quality with the expense of increased data rate, you can use higher sample rates, for

example 16 kHz.

9.4.6 Example Code

The following code initializes IMA ADPCM encoding on VS1003b/VS1023 and shows how to read the

data.

const unsigned char header[] = {

0x52, 0x49, 0x46, 0x46, 0x1c, 0x10, 0x00, 0x00,

0x57, 0x41, 0x56, 0x45, 0x66, 0x6d, 0x74, 0x20, /*|RIFF....WAVEfmt |*/

0x14, 0x00, 0x00, 0x00, 0x11, 0x00, 0x01, 0x00,

0x40, 0x1f, 0x00, 0x00, 0x75, 0x12, 0x00, 0x00, /*|........@......|*/

0x00, 0x01, 0x04, 0x00, 0x02, 0x00, 0xf9, 0x01,

0x66, 0x61, 0x63, 0x74, 0x04, 0x00, 0x00, 0x00, /*|.......fact....|*/

0x5c, 0x1f, 0x00, 0x00, 0x64, 0x61, 0x74, 0x61,

0xe8, 0x0f, 0x00, 0x00

};

unsigned char db[512]; /* data buffer for saving to disk */

Version 0.6, 2005-01-05

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