[sdiy] the white whale - modular synth patch memory

[Roman Sowa]

You can make digipot-type retrofits only when it absolutely needs 
variable resistance, like basic ADSR. In lots of cases it's just voltage 
or attenuation what's needed, so a simple filtered DAC directly or 
controlling a VCA will do the job.
And you cannot actually hear any zipping noise in ADSR pots.

Roman

W dniu 2015-03-18 o 17:19, Richard Moore pisze:
> 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.
>
> -rkmoore
>
>
>
>
>
> On Wednesday, March 18, 2015 10:50 AM, Paul Maddox <yo at VacoLoco.net> wrote:
> problem is, you want to store the parameter values as well as the
> patching to get true patch storage..
> suddenly everything get really complex and you start locking our vendors
> of modules if you do something bespoke.
>
>
>
>
> On 18/03/2015 01:48, Richard Moore wrote:
>> I couldn't resist.  I'm planning a DIY modular and I haven't yet convinced myself that patch memory is too ambitious.
>>
>>
>> And yes, I did check the archives.  It sounds like different concepts have been kicked around on the list for modular patching busses and patch memory for 20 years.  I probably missed a bunch of good stuff, though.  If you know of someone who has done a good job of this in their system, let me know.  I would very much like to see it.
>>
>>
>> The strategies seem to be:
>> 1. Switch matrices.
>>
>> 2. Sample everything and send lots of data on a digital bus.
>>
>> 3. Octopus modules (like WMD sequential switch).
>>
>> 4. Analog signal buses.
>> 5. Use a software modular (Pd, MAX/MSP, etc) instead
>>
>> 6. Why would you want to store patches on a modular?
>>
>>
>> There will always be use cases for #5, but everyone on this list is probably already convinced of the virtues of hardware.  Pin/switch matrices make for very clean modular synth builds, but they're not easily expanded.  Sampling and sharing a digital backplane is a good option, but may beyond my skills/time constraints/budget for a DIY modular.  #3 is limited and inelegant.  Right now I'm thinking about #4.
>>
>>
>> Here's how I think a useful modular patching bus and memory should behave:
>> 1. Patch memory - It should be able to route module inputs and outputs.  Hopefully without some patch cable octopus that keeps you from using the jacks normally.
>>
>> 2. Easy patch storage - You should be able to patch your system with cables and have that configuration stored to be recalled by a bus patching module later.
>> 3. Ability to edit - You should be able to load a patch, patch in additional modules, and save an edit.
>>
>> 4. Portability - You should be able to share patches with people that have similar modules.  Moving your modules around shouldn't break the patch memory.
>> 5. Knob position storage - Ideally knob positions could be stored and recalled until edits are made.
>> 6. Retrofitting - It would be really nice to be able to retrofit modules from commercial makers to make use of patching buses.
>>
>>
>> Here are my current thoughts:
>> 1. Have ~16 signal buses available on the backplane that modules can connect to (like in the ARP 2500)
>>
>> 2. Give every input and output on each of my modules an analog multiplexer (there are 8 channel ones on Mouser that start at <$1)
>>
>> 3. Have a single module that stores patches and commands the multiplexers (over SPI or I2C, perhaps).
>> 4. Assign some kind of ID to modules or module types to allow for storage of portable patches.
>> 5. Have a microcontroller that can "ping" the module inputs/outputs to determine where patch cables are for patch storage.
>>
>>
>> I've got some thoughts for knob position storage and retrofitting, but nothing certain yet.
>>
>> What else should I be thinking of?  Who else's synth should I be looking at?
>>
>>
>> -rkmoore
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