Creative SB0350 Hardware Programming Guide - Page 36

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Digitized Sound I/O Programming 3-7 ADPCM DMA mode The compression technique used by the DSP is known as ADPCM (Adaptive Delta Pulse Code Modulation). This technique stores the difference between data values instead of the actual data. The DSP supports decompression in the output process only. The first byte of the compressed data is always a reference byte. It is not ADPCM code but an actual data byte value. This byte is used by the DSP as a reference during the data decompression. There are three ADPCM compression techniques supported by the DSP: 8-bit to 2bit, 8-bit to 3-bit, and 8-bit to 4-bit. There are two different sets of output commands used to operate on data blocks. The first block of data to be transferred, which contains a reference byte, uses one set of commands. The subsequent blocks, which do not contain reference bytes, use another set of commands. Refer to the chapter "DSP commands" for details on using these ADPCM output commands.

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Digitized Sound I/O Programming
3-7
ADPCM DMA mode
The compression technique used by the DSP is known as ADPCM (Adaptive Delta
Pulse Code Modulation).
This technique stores the difference between data values
instead of the actual data.
The DSP supports decompression in the output process
only.
The first byte of the compressed data is always a
reference
byte.
It is not ADPCM
code but an actual data byte value.
This byte is used by the DSP as a reference during
the data decompression.
There are three ADPCM compression techniques supported by the DSP: 8-bit to 2-
bit, 8-bit to 3-bit, and 8-bit to 4-bit.
There are two different sets of output commands used to operate on data blocks.
The
first block of data to be transferred, which contains a reference byte, uses one set of
commands.
The subsequent blocks, which do not contain reference bytes, use
another set of commands.
Refer to the chapter "DSP commands" for details on using
these ADPCM output commands.