VS1033C Datasheet, PDF (46/74 Pages) List of Unclassifed Manufacturers – MP3/AAC/WMA/MIDI AUDIO CODEC

VLSI
Solution ^y
VS1033c PRELIMINARY
VS1033C
9. OPERATION
Each IMA ADPCM block is 128 words, i.e. 256 bytes. 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.
9.4.3 Adding a RIFF Header
To make your IMA ADPCM file a RIFF / WAV file, you have to add a header before the actual data.
Note that 2- and 4-byte values are little-endian (lowest byte first) in this format:
File Offset Field Name
Size Bytes
Description
0 ChunkID
4 ChunkSize
8 Format
12 SubChunk1ID
16 SubChunk1Size
20 AudioFormat
22 NumOfChannels
24 SampleRate
28 ByteRate
32 BlockAlign
34 BitsPerSample
36 ByteExtraData
38 ExtraData
40 SubChunk2ID
44 SubChunk2Size
48 NumOfSamples
52 SubChunk3ID
56 SubChunk3Size
4 "RIFF"
4 F0 F1 F2 F3
File size - 8
4 "WAVE"
4 "fmt "
4 0x14 0x0 0x0 0x0 20
2 0x11 0x0
0x11 for IMA ADPCM
2 0x1 0x0
Mono sound
4 R0 R1 R2 R3
0x1f40 for 8 kHz
4 B0 B1 B2 B3
0xfd7 for 8 kHz
2 0x0 0x1
0x100
2 0x4 0x0
4-bit ADPCM
2 0x2 0x0
2
2 0xf9 0x1
Samples per block (505)
4 "fact"
4 0x4 0x0 0x0 0x0 4
4 S0 S1 S2 S3
4 "data"
4 D0 D1 D2 D3
Data size (File Size-60)
60 Block1
256
First ADPCM block
316 . . .
More ADPCM data blocks
If we have n audio blocks, the values in the table are as follows:
F = n × 256 + 52
R = F_s (see Chapter 9.4.1 to see how to calculate F_s)
B
=
Fs×256
505
S = n × 505. D = n × 256
If you know beforehand how much you are going to record, you may fill in the complete header before
any actual data. However, if you don’t know how much you are going to record, you have to fill in the
header size datas F , S and D after finishing recording.
The 128 words (256 bytes) of an ADPCM block are read from SCI HDAT0 and written into file as
follows. The high 8 bits of SCI HDAT0 should be written as the first byte to a file, then the low 8 bits.
Note that this is contrary to the default operation of some 16-bit microcontrollers, and you may have to
take extra care to do this right.
A way to see if you have written the file in the right way is to check bytes 2 and 3 (the first byte counts
as byte 0) of each 256-byte block. Byte 3 should always be zero.
Version 0.9, 2006-08-15
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