[sdiy] the white whale - modular synth patch memory

[Tom Wiltshire]

I think this is overly negative. Whilst retrofitting an entire existing analogue modular synth would be a major pain in the posterior, there are plenty of worthwhile stopping-off places on route, and plenty of places that might become the destination whilst you get there.
Furthermore, someone else already mentioned things like the Matrix12 - why not build something like that? These days you could build a "Nord Modular-ish" with a hardware interface, and do a lot of the routing and modulation in the digital domain behind the panel, and save the analogue side for some of the "flavour" elements, like filters, and VCA distortion and so forth. Ok, so it won't be a 1968 Moog system with patch memory, but that was never going to happen anyway. It'll still be an extremely versatile and useful instrument, and it might stay in tune too.

My own experience has been that as long as the interface feels analog, the overall experience is the same, even if the module is digital at its heart. I've designed and built more than enough envelopes and modulators to have proved this by now, even on cheap hardware. However, I've also learned that *as soon as* you start putting "modes" into the interface, the illusion is shattered and the thing starts to be a pain to use. Stuff like that is a dead giveaway - same as audible parameter stepping, aliasing, etc etc.
In short, I think it can be done, but I don't think it can be retrofitted to an existing analogue modular. So I guess we agree, Neil, really.

Tom


On 18 Mar 2015, at 21:39, Neil Johnson <neil.johnson71 at gmail.com> wrote:

> *sigh*
> 
> This old chestnut, rearing its ugly head once more.  Time to get the
> dead horse out again....
> 
> Richard Moore wrote:
>> I think you've hit the softest spot, Paul.  Right now my best thought is to replace the pots on a retrofitted module with a little board containing a pot and a digipot.  The digipot could be controlled by the pot or could receive a value from the CAN bus.  Between the digipots and the analog muxes there could be full patch memory.  I don't like the resolution of switching noise of the digipots, though, so I'm not sold on this concept yet.
> 
> Pots are used in many ways in analogue synth modules, some as simple
> potentiometers, others a variable resistors.  Sometimes strapped
> across the supply rails, others in op-amp feedback loops, others in
> critical signal junctions.  The application of potentiometers is
> sufficiently wide that a single digipot solution will not fit all, and
> digitpots have their own issues (stepping, maximum voltage/current,
> noise, non-linearities, etc).  The only truly transparent replacement
> would be motorised pots, in all the different track values (say 2k2 up
> to 2M2 in both linear and log, and some dual track as well).
> 
> The routing aspect is another tricky problem you won't solve.  There
> have been several comments along the lines of you won't use all the
> patches all the time, just a subset.  Which is true.  But that subset
> changes enormously.  And just thinking about the spec you need to beat
> - your switching/routing system needs to be as good as a length of
> shielded copper - no noise, no offsets, no distortion, extremely low
> coupling.  You need excellent DC performance for pitch CVs (gain,
> offset, minimal drift), and AC performance >50kHz if you want to keep
> those snappy envelope attacks and not suffer appreciable audio
> degradation after a few trips through your routing matrix.
> 
> And then there a multitude of switch types: push buttons, rotary,
> toggle, slide, and so on. A general solution would also need to cope
> with the "intelligent" synthesizer modules that have menus and sub
> menus - retrofitting into them could be entertaining.
> 
> If you want to get an idea of where you're heading check out the
> professional audio realm.  The closest would be mixing desks, and they
> either went down the VCA route and/or flying faders.  I think the
> closest to where you're heading would be the gear made by Bettermaker:
> http://www.bettermaker.eu/
> But they're not cheap.
> 
> Neil
> --
> http://www.njohnson.co.uk
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