[sdiy] Which programable chip?

[Roy J. Tellason]

On Thursday 16 April 2009 01:26:58 am Colin Hinz wrote:
> On Thu, 16 Apr 2009, Roy J. Tellason wrote:
> > On Wednesday 15 April 2009 04:34:52 pm Scott Nordlund wrote:
> >> Why would you need to run the audio through the processor?
> >>
> >> If I'm not mistaken, are you wanting to route one input (of 8 total) to
> >> one output (of 8 total)?  You can do that with 2 4051 multiplexers, and
> >> not have to worry about any ADCs or DACs or high speed processors or
> >> anything. You only need to send 6 bits to control everything.
> >>
> >> And if you want to be able to route multiple signals simultaneously, it
> >> may be slightly more complicated (depending on whether you want
> >> arbitrary routings, etc.)- you may need a crosspoint matrix, even 16
> >> 4066 chips (or similar), but it's the same basic idea to use analog
> >> switches to do the work.
> >
> > Speaking of which,  I've had some idle thoughts now and then about
> > running signals through those parts.  But you need to worry about signal
> > levels,  and they probably oughta be kept fairly low,  not typical synth
> > levels,  but more like "line" level as I understand it.  And if you want
> > to use those parts with their 15V maximum supply voltage and a
> > zero-centric signal level without AC coupling you'll need a pair of 7.5V
> > supplies,  right?
>
> Somewhere or another I remember seeing an appnote which suggested
> using the analog muxes to switch inputs into the virtual ground
> summing junction of an op-amp.
>
> I've gone digging for it, but lamentably I don't seem to have a softcopy.
> And no, I can't even remember who published it.....
>
> Ring any bells, anyone?

Not here,  but I do like that idea,  since apparently those parts are 
sensitive to where you are in terms of DC levels,  and will add some 
distortion to the signal from what I've read someplace or other...


-- 
Member of the toughest, meanest, deadliest, most unrelenting -- and
ablest -- form of life in this section of space,  a critter that can
be killed but can't be tamed.  --Robert A. Heinlein, "The Puppet Masters"
-
Information is more dangerous than cannon to a society ruled by lies. --James 
M Dakin