[sdiy] S&H

[Forbes, William - EE - UK/Leamington]

That's why most polysynths ARE all DSP.
Its nothing to do with lazyness it's all down to cost.

Bill.

> -----Original Message-----
> From: Paul Maddox [mailto:P.Maddox at signal.qinetiq.com]
> Sent: 17 January 2003 11:44
> To: synth-diy at dropmix.xs4all.nl
> Subject: Re: [sdiy] S&H
> 
> 
> William,
> 
> >So now you know why most commercial polysynths are all digital!
> 
> No, thats just laziness on their part..
> its easier to use a DSP and get 16 identical sounding filters 
> than to try
> and scale/adjust 16 analogue filters.
> you can also replace the entire synth architecture if you 
> want with dsp,
> cant do that with mixed digital/analogue.
> 
> Paul
> 
> 
> 
> > -----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
> >
> >
> >
> 
>