[sdiy] Bus for digital patching of synths

[cheater00 .]

Hi Tom,
thanks for your email, that's some well worded criticism and ideas.

On Sat, Nov 9, 2013 at 1:40 PM, Tom Wiltshire <tom at electricdruid.net> wrote:

> It seems to me that instant patch recall is the potential "killer feature" here, and what's proposed doesn't offer that, or not without a lot more work, anyway. Without that, it seems like an awful lot of technology to throw at a simple problem.

Yes - definitely, the digital patching makes much less sense on its
own. I've decided to discuss it on its own to rid the conversation of
preconceptions. The first thing that pushes you forward is if you want
digital patch storage. Another is that - if you're doing a polyphonic
synth - the front panel needs to be replicated to all the copies of
the analog circuit. I'm told analog replication on this order of
magnitude might be finnicky.

> I'm not sure I'm convinced that there's any need or any point to the proposed device. Essentially it's a big pile of digital patch cords, right? ADC at one end, DAC at the other, and digital routing in the middle. If that's all it does, it seems to me that Brian W is completely right - CMOS crosspoint switches are a much simpler way to do it. You get all the programmability, since you'll need a uP controlling the switches, but all the signals stay analog, and you avoid problems with DACs tending to either be good for DC voltage accuracy, or good at audio rates, but rarely both.

It doesn't have to be a dumb system. You can implement digital signal
processing such as mixers, shapers, etc in DSP on the target. Just a
mixer per input and mult per output is a huge, huge help, and can be
realized with just a tiny bit of silicon, or on the crossbar. I
remember seeing pretty good offerings on DACs with a small micro built
in.

> On the other hand, if you're going digital, why have more than a few specialised analog processing modules. You could do the processing or sound generation with digital modules and avoid the need for more ADCs - just send the digital signals straight to the bus. There are plenty of digital oscillators and digital modulators on the market, and we can imagine the same units with a digital output.

The idea is to remove the bad parts, not the good parts :-)

Cheers,
D.