Sega CD PCM format?

[Raster]

What is the format of Sega CD PCM? It seems to be a modified form of an ADPCM. Is this correct?

 

[Borisz]

well, the chip can use a max of 32khz I believe, aside from that the format is probably game-specific.

Sonic CD for example does not use ADPCM I think.

 

[Mask of Destiny]

The chip doesn't use ADPCM. It uses the little used simple sign bit format. Rather than using two's complement for positive and negative values it instead has a 7-bits of magnitude and a simple sign bit. Sound Forge supports this format.

So 0xFF is -127 instead of -1. Charles MacDonald dug up a PDF datasheet of a compatible chip and I've got it on my site (www.retrodev.com) in the Sega CD section. It goes into fairly good detail, but you'll have to adjust all the frequency calculations they give as the chip in the Sega CD runs at 12.5MHz and I believe the examples in the datasheet use 8MHz or so.

 

[Raster]

Originally posted by Mask of Destiny@Tue, 2005-07-26 @ 11:33 AM

The chip doesn't use ADPCM.  It uses the little used simple sign bit format.  Rather than using two's complement for positive and negative values it instead has a 7-bits of magnitude and a simple sign bit.  Sound Forge supports this format.

So 0xFF is -127 instead of -1.  Charles MacDonald dug up a PDF datasheet of a compatible chip and I've got it on my site (www.retrodev.com) in the Sega CD section.  It goes into fairly good detail, but you'll have to adjust all the frequency calculations they give as the chip in the Sega CD runs at 12.5MHz and I believe the examples in the datasheet use 8MHz or so.

Does the generated pcm data have to be aligned to even bytes?

The Lunar PCM to WAVE convert mentions something about this.

 

[Mask of Destiny]

PCM samples have to start on a 256byte boundary in PCM RAM as the start address register is only 8-bits wide so it only provides the upper 8-bits of the start address. The repeat address has full 16-bit resolution however.

 

[Raster]

Thanks for the help, I got it all working.