Inside Macintosh: Sound /

Chapter 2 - Sound Manager / Sound Manager Reference

Sound Manager Routines / Compressing and Expanding Audio Data

Comp6to1

You can use the Comp6to1 procedure to compress sound data at a ratio of 6:1.

PROCEDURE Comp6to1 (inBuffer: Ptr; outBuffer: Ptr; cnt: LongInt;
                     inState: Ptr; outState: Ptr; 
                     numChannels: LongInt; whichChannel: LongInt);

inBuffer

A pointer to a buffer of samples to be compressed.

outBuffer

A pointer to a buffer where the samples are to be written.

cnt

The number of samples to compress.

inState

A pointer to a 128-byte buffer from which the input state of the algorithm is read, or NIL. To initialize the algorithm, this buffer should be filled with zeros.

outState

A pointer to a 128-byte buffer to which the output state of the algorithm is written, or NIL. This buffer might be the same as that specified by the inState parameter.

numChannels

The number of channels in the buffer pointed to by the inBuffer parameter.

whichChannel

The channel to compress, when numChannels is greater than 1. This parameter must be in the range of 1 to numChannels.

DESCRIPTION

The Comp6to1 procedure compresses cnt samples of sound stored in the buffer specified by inBuffer and places the result in the buffer specified by outBuffer, which must be at least cnt/6 bytes in size. The Comp6to1 procedure works much like the Comp3to1 procedure, but compresses every 48 bytes of sound data to exactly 8 bytes of compressed sound data and compresses remaining bytes to no more than one-sixth the original size.

SPECIAL CONSIDERATIONS

Because the Comp6to1 procedure might allocate and dispose of memory, you should not call it at interrupt time.

ASSEMBLY-LANGUAGE INFORMATION

The trap macro and routine selector for the Comp6to1 procedure are

Trap macro	Selector
_SoundDispatch	$000C0010