[sdiy] Bus for digital patching of synths

[rsdio at sounds.wa.com]

On Nov 8, 2013, at 02:42, cheater00 . wrote:
> We have an analog modular. It uses a lot of patch cables, which can  
> get difficult to manage, and becomes even worse in consideration of  
> polyphonic modulars. Instead, put an ADC on each output and a DAC  
> on each input and connect them with the right bus. As a nearly free  
> bonus you get patch storage. The question is what bus is right.


Sorry, but not all analog knobs can be replaced by a DAC. You're not  
going to get patch storage for all aspects of your modular settings -  
just the CV routing. With certain circuits, you'll need to convert a  
variable resistance control into a voltage control. Just because you  
can automate all the CV inputs to a module doesn't mean you can call  
up any patch on that module as if you're tweaking the knobs. For  
example, there are pots to scale the incoming CV, filters with  
resonance that aren't voltage-controlled, etc. Move any of those  
knobs and suddenly your "patch" fails to produce the same sounds. In  
other words, I wouldn't call this a free patch storage, because it's  
not going to deliver what synth players typically expect from calling  
up a patch.

Have you looked at what Buchla does for digital patching?

I imagine that you might get a lot more mileage out of a totally  
analog switching matrix, using CMOS and/or FET switching. Sure,  
digital control of the switches, with patch storage in the CPU system  
controlling the matrix, but you can skip the digital quantization.  
Most importantly, you'll avoid the sample rate issues by keeping all  
the CV pure analog.

Look at what Steven Roberts has done with the Microship, BEHEMOTH,  
and other electronic circuit publications. He designed and used an  
audio crossbar that could send any analog signal from any source to  
any destination. All CMOS, if I recall correctly. No ADC, DAC, or  
problems with bandwidth, sampling, or quantization. Just our friend  
the noise floor.

Brian Willoughby
Sound Consulting