JEITA CP-3451
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The m-Law audio data contained in data-ck is packed as shown in Figure 42. Here the left-hand byte stores the
lower address and the right-hand byte holds the upper address.
m-Law monaural
Sample 0
Sample 1
Sample 2
Sample 3
Channel 0
Channel 0
Channel 0
Channel 0
Byte 0
Byte 1
Byte 2
Byte 3
m-Law stereo
Sample 0
Sample 1
Channel 0
(left)
Channel 1
(right)
Channel 0
(left)
Channel 1
(right)
Byte 0
Byte 1
Byte 2
Byte 3
Figure 42 Packing of m-Law Audio Data
5.5.4 Basic Structure of IMA-ADPCM Audio Data
IMA-ADPCM audio data is 4-bit data obtained by compressing 16-bit linear PCM audio data. IMA-ADPCM, as seen
in its other name DVI-ADPCM, uses a compression algorithm originally developed by the Intel DVI Group (DVI:
Digital Video Interoperability). It was later adopted by the IMA (Interoperability Multimedia Association) as a
standard audio data format.
Details of the IMA-ADPCM algorithm are given in the IMA Digital Audio Doc-Pac and other documents.
When the format type is IMA-ADPCM (DVI-ADPCM), the basic structure is as shown in .
A fact-ck is recorded as with the m-Law format, but a difference from that format is the larger fmt-ck size (in addition
to a cbSize field there is a wSamplesPerBlock field).
Address Offset
Code
Meaning
(Hex)
(Hex)
+00
52
+01
49
+02
46
+03
46
"RIFF"
(ckID)
+04
ckSize
(4 Bytes)
+08
57
+09
41
+0A
56
+0B
45
"WAVE"
(formType)
+0C
fmt-ck
(28 Bytes)
IMA-ADPCM format information (size is 28
bytes fixed)
+28
fact-ck
(12 Bytes)
Samples per channel-unit block
(IMA-ADPCM format)
+34
data-ck
PCM format audio data
Figure 43 Basic Structure of IMA-ADPCM Format
