[Coco] Assembly audio routines

[Zippster]

Bill,

Arithmetic shift or logical?  That still seems weird to me, but then again, I have no idea
what data they are starting with.  Got a link to the source code?  Might be interesting
to read through.

- Ed


> On Mar 20, 2017, at 7:42 PM, Bill Pierce via Coco <coco at maltedmedia.com> wrote:
> 
> Maybe the software is shifting to the right then. I'll have to look. It's been a bit since I dug into the Musica source, which I know does a shift on every 8 bit value after generating the samples from an 8bit freaquency table. I do know that if you comment out that shift loop, the sound is a little grainier. If I comment it out and route to the orch90, it's clean.
> The only reason Musica preserves the 8 bit values in the file and only does the shift loop before play is that Musica supported the "Speech Systems Stereo Pak" which was like the orch90 (8 bit stereo DACs) but without the rom. When the Stereo pak is selected as output, the shift is skipped, leaving the 8 bit values intact.
> 
> I just checked the source and it does shift 2 bits to the right. So you guys are right. The comments state it's shifted to "normalize" the byte for the 6 bit DAC.
> 
> 
> Bill Pierce
> "Charlie stole the handle, and the train it won't stop going, no way to slow down!" - Ian Anderson - Jethro Tull