[sdiy] Which programable chip?

[Colin Hinz]

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?

- Colin