[sdiy] Reverse engineer an EPROM encoding?

[Scott Nordlund]

At least Yamaha, Casio and apparently Kawai used the log-multiplication thing, though it wasn't universal. The Synclavier and Synergy didn't use it. It's an easy way to scale something digitally, provided you don't need interpolation or filtering (which both require actual multipliers). I think the idea is that the sign bit should be sent straight to the output, bypassing the exponential table. There's an example table here: http://yehar.com/blog/?p=665


> Date: Thu, 17 Oct 2013 09:41:52 -0700
> From: grant at musictechnologiesgroup.com
> To: gsn10 at hotmail.com; tom at electricdruid.net
> CC: synth-diy at dropmix.xs4all.nl
> Subject: Re: [sdiy] Reverse engineer an EPROM encoding?

> 
> It is a multiplying DAC, but Vref is fixed. Your comments make perfect 
> sense... volume control by addition.  And Kawai was probably down the 
> street so to speak from Yamaha. So is there any common logarithmic 
> method from that period?  Should I just try log10 or loge and see what 
> pops out?
> 
> I'm dealing with 11 data bits plus sign. And the chord/step DAT thingy I 
> described (that resembles u_law) provides a close approximation. Not 
> close enough mind you. So I guess u-Law is a similar logarithmic method.
> 
> I don't have my Hal Chamberlin book handy, buy perhaps he discusses this...?
> 
> GB