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Sorting voltages?
MUFF WIGGLER Forum Index -> Modular Synth General Discussion  
Author Sorting voltages?
ETSUKO
Hi there,

I was wondering if it's possible to sort 4 voltages from low to high, so to distribute a 4-voice chord over 4 oscillators in a desired order?

Setup is as follows: ROLI Seaboard [4-voice chord] > Polyend Poly [ch 1-4] > 1x 'bass' oscillator, 3x other oscillators

At least I'd like the lowest pitch always to be on the 'bass' oscillator. I found a Doepfer Minimum/Maximum module (A172), would this work? Or would there be any option to sort all four voltages?

Thanks in advance.
Navs
You're looking for some sort of window comparator/multiplexer maybe, like the Doepfer A-152 or Toppobrillo Mixiplexer.
Sugarfree
what should happen if you hold 3 voices and add another note in the middle?

what you're looking for is usually a part of a polyphonic MIDI-to-CV converter.
Different methods of voice allocation and priority.

not sure if this is it, but check out http://www.edv-technik-ts.de/html/muc-810-eurorack.html
Sugarfree
another idea: an arpeggiator + sequential clock divider with reset + sample and hold
Synthiq
ETSUKO wrote:
I was wondering if it's possible to sort 4 voltages from low to high, so to distribute a 4-voice chord over 4 oscillators in a desired order?

If the question is if there is a standard module that can do it, I have not seen any. But it is possible to design such a circuit. It only takes 6 comparators to compare all 4 inputs to each other and then you "only" has convert these 6 comparator outputs to control signals for 4 4-to-1 analog multiplexers so any of the 4 inputs can be routed to any of the 4 outputs to the VCOs. The logic to convert the 6 comparator outputs to the mux control signal will be the messy one. It might be easier to just read the 6 signals into an Arduino and do a table lockup and send the result to control the multiplexers. Or you can skip the comparators and use the ADC in the Arduino to measure the 4 input voltages and do all calculations in software but it will be slightly slower.

Sugarfrees comment about what should happen when one of the notes change is very relevant and must be considered before any design is done. You probably don't want to switch from one oscillator to another in the middle of a note.
dkcg
I don't know much about the Roli, but you could do this on the midi end with something like MaxMSP. Separate it out so the lowest note goes out channel 1, the rest go out through channel 2 (or however you want to split the signals).

You would need 2 midi to CV modules, or maybe one per channel you split it out to.
Navs
I missed the bit about the Roli, which I don't know much about either, but if it outputs MIDI the solution is easier with something like Logic's Environment or, as dkcg writes, MaxMSP.

Similar to Sugarfree's suggestion, the Kenton Pro 2000 II MIDI -to-CV converter has a polyphonic mode for assigning chords.
Parnelli
It sounds like at the end of the day the need is for four notes of MIDI to be transposed to four CVs, there are a number of modules that will do this. My MIDI 3 only does two at a time, but there are others that will, I'm sure of it.
mskala
If you want to do it with CV input, probably the easiest and most flexible thing is to connect a CV-to-MIDI module into a MIDI-to-CV module. Those would probably have enough options to allow setting any reasonable note priority.

Working just on the pure voltages, it seems like you could do it with A-172 modules by building a sorting network - see https://en.wikipedia.org/wiki/Sorting_network. I think a complete sort needs five of them, but pulling out just the lowest voltage and leaving the other three unsorted would only require three modules. Each module is configured to sort just two voltages at a time. Outline for the three-module patch: one module finds minimum and maximum of voltages A and B, one finds minimum and maximum of voltages C and D. The two maximum outputs are obviously not the lowest voltage, so you can use those directly. Then the two minimum outputs go into the third module, which finds the global minimum for your bass note, and the last remaining voltage.

I'm not sure this would really work well in practice because the A-172 may not be accurate enough. I haven't used one, and the Doepfer page implies there may be significant gain and offset inaccuracy. But even if real modules aren't good enough to implement it, it's fun to think about how the patch would work in theory.
ETSUKO
Hey guys, thanks a lot for all the replies!

Sugarfree wrote:
another idea: an arpeggiator + sequential clock divider with reset + sample and hold


Sounds interesting... How would this work? Any suggestions for particular modules that it would involve?

Sugarfree wrote:
what should happen if you hold 3 voices and add another note in the middle?


It should re-sort the voltages, so that they remain distributed from lowest to highest note.

dkcg wrote:
I don't know much about the Roli, but you could do this on the midi end with something like MaxMSP. Separate it out so the lowest note goes out channel 1, the rest go out through channel 2 (or however you want to split the signals).


I'm aware that Max/MSP offers solutions in this case, but my live-setup is kinda laptop-free...

I'd be open to a similar Eurorack solution however - I've been looking at the Monome Teletype. Haven't been able to figure out if it'd be capable of doing this particular thing though.

Parnelli wrote:
It sounds like at the end of the day the need is for four notes of MIDI to be transposed to four CVs, there are a number of modules that will do this. My MIDI 3 only does two at a time, but there are others that will, I'm sure of it.


Maybe you're simplifying the question a bit too much? I've looked into the MIDI 3 (from Pittsburgh Modular I assume), but it doesn't sort the notes, does it?


@mskala - thank you vm for your reply. I think your patch idea would actually work. I dove a bit deeper into the manual and saw some Youtube videos on the A172. They indeed suggest to use an offset module with it, but I think this is for more creative purposes than technical ones - see the screenshot I attached, this is one A172 input/output example where you might need to use offset/amplitude correction for.

At €55 each, 3 (or even 5) of these modules is actually a relatively cost effective way to achieve it I guess.

If anyone knows a module that achieves the sorting thing already on the MIDI side, I'd also be interested in that, too. Whatever does the job smile once more thx for all the help already.
slow_riot
hard, almost to the point of being unfeasible in "analogue", effortless with DSP. If you really don't want to use a computer the Rebel Technology OWL can run Max/MSP patches.
Sugarfree
ETSUKO wrote:

Sugarfree wrote:
another idea: an arpeggiator + sequential clock divider with reset + sample and hold


Sounds interesting... How would this work? Any suggestions for particular modules that it would involve?


Every arpeggiator can already sort the pitches of a chord you hold and output an ordered sequence of voltages.
If you clock it really fast, you could use a sequential switch to distribute those voltages to 4 different oscillators.
Then, you could use a sample and hold module before each oscillator, to make sure they play a chord, not just a sequence.

The arpeggiator, sequential switch and sample and hold modules would all need to be clocked from one source. The S&H hold time would be 1/4 of the clock speed.

In addition to this, each time you press a key, you could send a reset gate to both the arpeggiator and the sequential switch to make sure that your chords don't flip.
Sugarfree
An additional benefit of using an arpeggiator would be real time quantization of what you play. Depending on the master clock speed.

(if you wanted to auto-quantize your playing to 16th notes, you would need set the master clock to 1/64. Assuming 4-note chords)
fac
Just to throw another option out there:

The SSL V-Gates can take an input voltage and output a gate signal from one of up to 8 different gate outputs, depending on how high the input voltage is. You can then use these gates to switch between waveforms (if you have enough VCAs and a mixer).

https://steamsynth.com/shop/euro-modules/v-gates-euro-model-2610/

Plus it can do a lot more. It can also run the gates in sequence or in random order. It's a great module for adding life to sequences and arpeggios.
fac
Another option is the SSL Segwencer IV, but I'm not sure if it's available in euro.rack.
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