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Control Voltage to and fro
MUFF WIGGLER Forum Index -> Modular Synth General Discussion  
Author Control Voltage to and fro
epiphanius
Hi:

I am in need of a new audio interface as my Scarlett 8i6 is disconnecting from usb (tried with 2 pcs). A number of newer interfaces include dc coupled outputs, which is nice. I am looking at the Native Instruments Komplete Audio 6 mk2m, which has dc coupled outputs, but warns they are "Limited to +/-2V range due to the AUDIO 6 being USB powered." I have a single rack of Euro which includes a Pittsburgh SV-1, a Makenoise Maths and a Doepfer guitar input.

My question is: will I be able to control my modular using the Komplete Audio 6? If I have to increase the voltage using the SV-1, Maths, or both, could I get some direction on how to patch this?

I have a similar question about a Pigtronix Philosopher King, which has CV outputs for which "The range is approx. 2VDC  12VDC." If I want to use the cv from the Philosopher King with my Eurorack setup, do I need to use the Maths as a vca? Patching suggestions appreciated for this idea as well.

Thanks for reading and for any suggestions.
Agawell
have you tried using different cables as well as different PCs?

personally I'd go for one of the Expert Sleepers solutions for the audio interface - as they are specifically designed for interfacing computers and eurorack - in fact I did and am happy with my es8 - may upgrade to an es9, sometime in the future

yes a little bit more expensive, but also twice the i/o and all dc coupled, plus power is from rack not usb

or, iirc, RME have done dc coupled outs on (at least some of) their interfaces for years - maybe a used older one of these would work well (much higher end than the Kontact by the look of it)

you'll end up using all of math to process one cv - which is a bit of a waste of maths

I'd think something like a shades (attenuverter/offset) module would be a good investment for scaling the pigtronix cv out
epiphanius
Thanks, Agawell:

I'll look into the ES stuff - I do want to be able to record audio as well as output cv, and I had not considered ES for this (I am after a disting to fill the final spot on my single rack). I will also look into shades.

Another way of putting my question might be:

Can I increase the output voltage of a source (say, the PK or the NI interface) from, 2v to 5v simply by connecting the 2v source into a VCA of some kind and then turning that VCA up by 3v, e.g. to produce 5 volts? The arithmetic (which I am terrible at) adds up, but voltage is a funny thing, so I'm not clear that simple addition applies to voltages.

BTW I also have a Moog CP-251 that has attenuators (not -verters), and has a mixer...

Cheers,
e.
epiphanius
regrets for posting 2x in a row, but perhaps this can make my noob question more clear:

NI responded to a question about their new audio card here:

If a soundcard has DC coupled inputs and outputs it can "talk" to your modular without the need of any other interface. The +/-2V doesn't have an influence on that. 5v and 12v for modules are their power supply. So if you go for the Komplete Audio 6 MK2 (not the MK1 as it's not DC coupled) you're good to go

But, if their card only does +/- 2v, then it cannot control voltages up to 5v (nevermind 12v) unless it goes through an attenuverter that adds...3 volts.
Is this correct? Is their product more limited than a card that outputs +/- 5v ? Would a dc coupled card that outputs, say +/- 12 v be likely to damage a Euro module?

Thanks again,

e.
Agawell
hmm I think you have some gaps in understanding of the basics of modular synthesis

an attenuator/attenuverter will not increase the peak to peak voltage - it will only decrease it (attenuate it) or invert it (make +ve -ve and vice versa) and then decrease it (attenuverter)

in order to increase the peak to peak range you need an amplifier

most VCAs (Voltage Controlled Amplifiers) are not actually amplifiers, they are actually voltage controlled attenuators ie the highest point of the controlling envelope will output the same volume as the input

some ie the ones I mentioned above, are amplifiers (hence the +ve dB gain) - ie the highest point of the controlling envelope will output at +XdB compared to the input

it is unlikely that +/-12v input to a module will damage it - probably the worst is that it will be clipped

the problem with a +/-2v output is that it may not trigger some modules - when used as a gate/trigger and has a limited range when used for modulation and/or v/oct (you will only be able to get a 4 octave range out of it)

adding voltages (offsets) to this will do unusual and probably unwanted things
- gates/vcas etc may stay open as the voltage is never low enough to close them
- modulation will not go through 0 or to 0 even
- v/oct will either no longer be v/oct it will be spread out so that everything is out of tune or it will be much higher than intended and probably out of tune (you need a precision adder to guarantee adding 2 signals together is exactly the sum of the 2 signals)

I've not seen this unit before, but it looks like a half-assed attempt, due to little research of actual modules

the expert sleepers modules (es8/es9) are significantly better - they are dc coupled class compliant audio interfaces that are specifically designed for modular synthesis (as they are actual modules)

but as I said I would check your usb cable first!!!

it might be a really good idea to read through the first 20 or so articles in the sound on sound magazine "synth secrets" series (and maybe their 2 articles on modulars - although these are both a bit out of date now) - all available online - and/or get the patch and tweak book - in order to get a grip on what utility modules do what and how - (these are generally the bits that are there in fixed architecture synths - but often hidden away by the designer - and make modular all the more interesting for being accessible)
epiphanius
Thanks so much, Agawell: Indeed this question was mostly about trying to understand some of these basic concepts: I have read up on many of the concepts, including some from the SOS series, which is excellent, but was having a hard time putting them together regarding voltage in general, and you have greatly assisted this. I will be spending a fair bit of time with your generous explanation - it's a great start to my weekend which will be spent applying your insights. I'll also get back to the S0S series, thanks for the pointer.

Quote:
most VCAs (Voltage Controlled Amplifiers) are not actually amplifiers, they are actually voltage controlled attenuators


Mind blown. This is probably where my difficulty in understanding started.

I will stay away from the NI box for the reasons you indicate here - I did think those types of issues could be an issue. I just popped over to CDM and saw this:

https://cdm.link/2019/11/motu-m2-m4-audio-interfaces/

It does have "DC coupled outs, but is 'usb powered', so in theory would suffer from the same issues as the NI one (no spdif tho, and I prefer to have that feature).

Quote:
have you tried using different cables as well as different PCs?


Different cables, disabled all usb devices, disabled and enabled other sound devices on the motherboard, different usb port types, with and without a hub: I now know more about Windows USB than, clearly, I knew about VCA. Hours of troubleshooting only to confirm there's an issue (an extensive message to Focusrite remains unanswered). Just about to test with an old Mac lappie as well.


Very best,

e.
Be Sandy?
Most standard audio interfaces will not output "full range" modular voltage levels. I'm not aware of one that does.

That is where the ES8 etc come into play as they have been designed specifically with modular in mind and output full range voltages.

If you are using a Mac you can create an aggregate device using an ES8 (for example) and a standard audio interface so you can use both together.

Might be worth having a look over in the Expert Sleepers subforum if that's something that sounds interesting.
https://www.muffwiggler.com/forum/viewforum.php?f=35
epiphanius
Yeah, I have an old mac and then got a firewire motu 8/in out for cdn $100, it's a good combo, and the aggregate device is a great feature.

Thanks,
e.
artieTwelve
I had a motu for a short time but I could never get the drivers to work/install properly. If you have a mac, the motu is a great interface. If you use windows, I would stay away from it. Granted, that was about 18 months ago. Things may have changed.

I have an ES-8 now and I'm very happy with it. The ES-9 is tempting but the 8 has everything I need for now.
Agawell
watch out if you have an older computer - es9 may not work as it's usb-c - I'd check with Os before buying!
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