[sdiy] S&H

[Forbes, William - EE - UK/Leamington]

So now you know why most commercial polysynths are all digital!


> -----Original Message-----
> From: Paul Maddox [mailto:P.Maddox at signal.qinetiq.com]
> Sent: 17 January 2003 09:54
> To: synth-diy at dropmix.xs4all.nl
> Subject: Re: [sdiy] S&H
> 
> 
> Richard,
> 
> > I'd doubt this. You'd be building something which leaves a 
> negative amount
> > of room for component tolerances. That's not usually a good idea.
> 
> This is why Im not keen on doing it.
> 
> > Why not buffer the incoming data with its own independent 
> (dual-port?)
> > memory, so you can stretch out the 32 channel update cycle 
> over the whole
> > of the 10us? It would be a bit of a pain to design but at 
> least you'd be
> in
> > digital land where things mostly have hard edges, and not 
> trying to deal
> > with the problem in a fuzzy analogue way.
> 
> Yeah, I've been thinking about this but there are two problems..
> 1) dual port memory is *VEY* expensive, 64Kbyte will cost about £40.
> 2) To do it in an FPGA would mean an insane amount of IO and 
> one DAC per
> oscillator.
> 
> > I don't know how you're driving the S&Hs or what you're 
> driving them with,
> > but this might make the specifications for your software 
> more relaxed too.
> 
> I was trying to use ONE DAC to generate 32 oscillators (for a 
> polysynth),
> but it looks like I wont be able to do it.
> so I'll try and find some quad/octal DACs that I can use 
> instead, its a
> shame, but its probably a better soloution than the 
> singleDac+S&H method, it
> just takes more board space...
> 
> Paul
> 
> 
>