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VLSI
Solution
y
VS1103b
VS1103B
7. OPERATION
7.4.3 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
"RIFF"
4
ChunkSize
4
F0 F1 F2 F3
File size - 8
8
Format
4
"WAVE"
12
SubChunk1ID
4
"fmt "
16
SubChunk1Size
4
0x14 0x0 0x0 0x0
20
20
AudioFormat
2
0x11 0x0
0x11 for IMA ADPCM
22
NumOfChannels
2
0x1 0x0
Mono sound
24
SampleRate
4
R0 R1 R2 R3
0x1f40 for 8 kHz
28
ByteRate
4
B0 B1 B2 B3
0xfd7 for 8 kHz
32
BlockAlign
2
0x0 0x1
0x100
34
BitsPerSample
2
0x4 0x0
4-bit ADPCM
36
ByteExtraData
2
0x2 0x0
2
38
ExtraData
2
0xf9 0x1
Samples per block (505)
40
SubChunk2ID
4
"fact"
44
SubChunk2Size
4
0x4 0x0 0x0 0x0
4
48
NumOfSamples
4
S0 S1 S2 S3
52
SubChunk3ID
4
"data"
56
SubChunk3Size
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 = Fs (see Chapter 7.4.1 to see how to calculate Fs)
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 IN0 and written into file as follows.
The high 8 bits of SCI IN0 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 2 should always be less than 90, and byte 3 should always be zero.
Version 1.01, 2007-09-03
39
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