VS1033 - MP3/AAC/WMA/MIDI AUDIO CODEC - VLSI Solution

VLSISolution yVS1033cVS1033C9. OPERATION9.4.4 Playing ADPCM DataIn order to play back your IMA ADPCM recordings, you have to have a file with a header as describedin Chapter 9.4.3. If this is the case, all you need to do is to provide the ADPCM file through SDI as youwould with any audio file.9.4.5 Sample Rate ConsiderationsVS10xx chips that support IMA ADPCM playback are capable of playing back ADPCM files withany sample rate. However, some other programs may expect IMA ADPCM files to have some exactsample rates, like 8000 or 11025 Hz. Also, some programs or systems do not support sample rates below8000 Hz.However, if you don’t 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 × 12 MHz and d = 12 isf s = 7812.5Hz. Because the frequency error is only 2.4%, it may be best to set f s = 8000Hz to theheader if the same file is also to be played back with an PC. This causes the sample to be played back alittle faster (one minute is played in 59 seconds).Note, however, that unless absolutely necessary, sample rates should not be tweaked in the way describedhere. 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 AD Startup TimeDepending on the external components it may take 2-5 seconds for the MIC and LINE bias to wakeup properly. You can reduce the settling time by changing the components. You can also speed up theprocess by enabling the AD with a low sample rate some time before the recording starts by writing0xc01e to SCI WRAMADDR, then 0x0800 to SCI WRAM. Notice that hardware and software resetdisables the AD.9.4.7 Example CodeThe following code initializes IMA ADPCM encoding on VS1033 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};Version 1.00, 2008-02-01 48