[sdiy] CC-Modular

[xmurz at gmx.de]

I agree with you. The point of this project was to get a 100% analog sounding synth with savable patch rountings.
By converting ad/da many times, even at 48khz you loose a lot of high end and impulse response.
The idea of using adc's to simplify is a really good idea, shure, but maybe for another project, where
the goal is a hybrid system sound. Analog means BIG, so this project will be big one way or the other.
You could always start off with 1vco 2lfo 1adsr 1vcf and expand the compexity like on a normal modular system.
However, you have to be careful with you design, you want it to be relatively easy to expand modules.
So maybe do something like a motherboard where all the connecting is being done and use sockets
to connect the module pcb's to the motherbards. For this the mohterboard would have to be scaled big enough,
so that you can expand enough modules, and it should be expandable itself (jumpers when adding 
more multiplexers etc.). And you may be able to include a connector to expand to 2 motherboards.
...
again, just some thoughts.

- Hans

10.09.02 02:33:32, Seb Francis <seb at is-uk.com> wrote:

>Hi JB,
>
>Interesting idea to use multiplexed DACs and ADCs and a "virtual" digital matrix to avoid the need for the switch matrix (this seems to be the bit which has the most scaleability problems).  This is not 
disimilar to the ideas which Paul mailed me, although he doesn't suggest using a multiplexed DAC.
>
>I didn't even realise there was such a thing like the MAX5631.  It looks really good (at least for CVs).
>
>I tried to work out from the datasheet whether it would be fast enough for 32x 48KHz.  I'm not sure that it is .. it seems the fastest it can run the sequencer clock is 120KHz (1/4 the max external 
clock rate of 480KHz).  So it can't update all the channels at anything more than 3.75KHz.  I might have got this wrong though ;)  This seems not to be enough for anything other than CVs (and even 
then fast envelopes and LFOs might be a problem).
>
>The other thing which would concern me is what all the converting to and from digital will do to the sound.  Even with high end professional ADCs and DACs I don't like running a signal backwards 
and forwards from analog to digital too many times.  It doesn't help the sound.  Consider a patch with VCO-VCF-MIXER-VCF-FX mixing with VCO-MIXER.  There's a lot of signal conversion going on.  
After all, the reason most people use analog (apart from the fact that a big cabinet full of knobs looks lovely) is because of how it sounds.
>
>Something like the MAX5631 does simplify producing many CVs from the computer & digital controller.  With this chip it looks like it is possible to run say 4 channels very fast for any soft-generated 
LFOs and envelopes, while running the rest slower for other CVs (would require some clever software to get the timing right!).  Also 16 bits is nice for slow soft-generated LFOs and envelopes (with 14 
bits used for the other CVs).
>
>Still the biggest problem is the size of analog switch matrix needed to connect a moderately large set of modules and CVs.  Ian Fritz made the suggestion to design an expandable system where 
banks of analog switches can be added as the number of analog modules grows.  I'm also looking for dedicated analog switch matrix chips which might reduce the scale of things.  Quality of switch 
matrix is also important.
>
>As for putting all the analog stuff on a PCI board - well this is fine as long as all modules of the synth would fit, and it wouldn't be possible to expand the system, and plug in modules from other 
systems like MOTM, etc..
>
>On a practical note, I've never had any experince soldering these tiny SMT chips like the MAX5631 (or most probably large analog switch matrices).  Can this be done by hand with a normal 
soldering iron?
>
>Seb