Source
r/synthdiy•
popctrl

Using PC as a cv source

I'd like to use something like Max MSP or Supercollider as a CV source for my euro rack synth.

I've seen the Expert Sleepers modules which seem to be perfectly suited for this application, but I'm curious about hacking this together with what I have.

I have a mini dsp udac8. Will this be able to output to my modular, or will the level be too low? What do I need to consider when looking at DACs? Will audio interfaces in general (such as the focusrite 18i20) be capable of outputting CV at the levels needed?

Posted Dec 17, 2019, 7:14 PM UTC

1240
Agawell•

Most audio interfaces are not dc coupled

This is a requirement regardless of volume for sending modulation (cv)

Ac coupling filters out low frequency signals as noise - so your modulation will be filtered out as it is low frequency

If you have a Mac then aggregate devices allow you to use 2 (or more?) audio interfaces at the same time

Apparently asio4all does this for windows but I have no experience and have heard varied reports

Otherwise if your audio interface has adat then maybe get a Es adat compatible module

The output level of anything not purpose built for eurorack woll most likely be too quiet

You can buy input modules

But anything that can amplify should work - veils or the intellijel quad vca will both give you 4 channels of amplification and allow cv control over it and mixing. If required

8
popctrlOP•

How much amplification can you get out of something like the intelijel quad vca? I assumed it wouldn't be much

1
Agawell•

Most vcas have 0db gain

Intellijel quad has +6db

Veils has +20db

2
thors-lab•

You don’t need too much amplification for this purpose. Line level is something like 0.9Vpp. It shouldn’t be hard to find a module that offers a gain of 10. You could also hack together something like this on protoboard extremely easily with something like an TL072 op amp and a couple resistors, and have it on a stage off your rack. Note you’d still have to find a way to connect the power supply if you did this.

1
JVM205•

Isn't it easier to convert the MaxMSP output to MIDI, and then use a MIDI to CV converter?

5
jepyangMB-6582, TTSH, GILBERT, Casios•

This was gonna be my suggestion as well. Mutable CVPal, for instance, would be much cheaper than getting an audio interface just for this.

4
thors-lab•

Can MIDI do arbitrary CV though? AFAIK midi can only do note numbers, right?

1
JVM205•

No, you can do al kinds of stuff with MIDI. Sending information about parameters happens via MIDI CC messages. I'm also still getting started with MIDI stuff so I might not be the greatest resource.

3
thors-lab•

This is really good news…

1
freakorgeek•

MIDI does 128 notes on/off messages and 128 "continuous control" or CC messages which are a 7 bit value from 0-127. 128 steps of granularity isn't exactly smooth which limits MIDI's usefulness for CV.

1
thors-lab•

Hmm, that sucks — but it looks like MIDI 2.0 supports 32 bit control change messages! When this is supported it should be possible to use MIDI 2.0 to send CV! :D

2
popctrlOP•

How close to audio rates can i get with a midi to CV controller? >100Hz isn't a requirement but it would be nice

1
greghcarr•

I have a Universal Audio Apollo 8 Thunderbolt 2 and I use the outputs mostly for CV to my eurorack modular using the free "CV Tools" pack for Ableton Live. The DC-coupling on the outputs and the fact that it plays (relatively) nicely with Windows were the reasons I got it. I read that the MOTU interfaces, which are also DC-coupled, are fantastic, but I also read more than once that they have a history of driver problems with Windows.

3
ubahnmike•

the 18i20 has a maximum output of 15.5dBu which translates to about 13Vpp. Say for yourself if that suits your modules. This is right before clipping but a solid 10Vpp should be doable.

AC coupling is a thing. I don´t know if the 18i20 has it. A reasonable circuit should go as low as a couple of Hertz. Certainly not to DC though. If you actually want DC you´ll need a DC coupled interface.

MOTU interfaces are kown to work well as they are DC coupled. There may be others.

2
Agawell•

18i20 is AC coupled - so no use whatsoever for CV

13Vpp may be a bit quiet - eurorack is upto 20Vpp (+/-10V)

MOTU, Expert Sleepers, some RME and there's a newish one - from a big manufacturer - not sure which, but the Vpp was pretty small +/-5V - as it's usb bus powered - all make or have made dc coupled interfaces - there's probably a few more but those are the common ones

2
ubahnmike•

"so no use whatsoever for CV"

CV is mostly AC unless you want DC for triggering notes or switching stuff. AC coupled outputs usually go down to some Hertz which only prevents you from doing super-slow modulations or pure DC.

1
Agawell•

I read this earlier and wanted to check the cut off frequency of most AC coupling -so I did it's about 30Hz - from a muffwiggler thread - and below the cut off there is degredation of signal and distortion - ie it's muddy unusable quiet crap

so what does 30Hz mean? that's 30 full cycles every second - that's very near audible range - 0-10v and back again! I would describe that as incredibly quick modulation - except possibly for FM, in which case it's a bit slow, but in reality most modulation is not FM

even 1Hz - once per second - is pretty quick modulation - it's the equivalent of rotating a knob all the way one way and back again - in a second, every second

almost all of my modulation is slower than that

it's more rotate this knob for me over 1/2 to 2 bars and back again over another 1/2 to 2, which is 0.5 to 0.125Hz at 120bpm

also v/oct is often down below 30Hz - so AC coupled is no use for that either

YMMV, but definitely for me and a lot of other people AC coupled interfaces for CV are useless

1
ubahnmike•

30Hz? Ok that’s bad. I’m tempted to do my own measurements. I agree that one Hertz is pretty high indeed but I meant that in a better-than-nothing type of context.

1
thors-lab•

The fact that the ES8, a >$500 module, is the only module that seems to do this is a real tragedy in my opinion. I’ve been thinking about this being my next module to create as I feel like it would be incredibly useful. I’m going to try to aim for the $150-200 price range for that module, but we’ll see.

Technically speaking it doesn’t make sense that the ES8 should be $500 as the components would be mostly digital, and generally speaking digital components are the cheapest. Even a gnarliest MCU is not going to cost you more than $8-12 in bulk. The rest of the module should all be DACs and ADCs plus the connectors which are also not pricey.

Looks like expert sleeps is charging this much merely because there’s no competition making the same module.

2
junkboxraider•

People are really quick to assert that “X is overcharging for Y!” based on little more than a wild-ass guess about the price of parts only, regardless of how accurate they are and totally disregarding all other possible costs that might go into designing, building, and supporting a piece of gear. Let alone whether the mfr is also trying to make a profit, regardless how modest, to keep their business actually running.

I’m no fan of “how dare you criticize unless you can do it better” arguments, but in these cases it’s just stupid to jump to conclusions so heedlessly.

6
thors-lab•

Of course I’m not a fan of such arguments either. But there is a basis for my argument:

As mentioned in another comment, the behringer UCA222 is a $30 audio interface with 2 ins and 2 outs. I haven’t looked inside, but it either relies on a monolithic USB audio chip like those from CMedia, or from some combination of cheap microprocessor and ADCs.

If they are using a CMedia chip, they also make a larger version with something like 8 ins and 8 outs that costs marginally more.

If they are using an MCU, a more potent MCU also costs marginally more.

Given that the basis of the design is the same, the $530 difference between these two modules must arise almost solely from RND. A manufacture as large as ES should surely sell enough to offset those RND costs with only a small fraction of their sales.

While I do think that ES is slightly overcharging for the module, I don’t blame them at all. This is a very well made and precise instrument, obviously made for professionals, and additionally there seems to be no competition. What I’m more shocked at is that nobody has yet made a hobbyist level version of these using the solutions I described above.

And yes I’m aware that in order to get that many channels you have to use USB-HiSpeed which seems to be significantly harder to implement. However, again I doubt that that difference in implementation is some $400 per module at volumes like expert sleepers is making.

1
lm13700•

I'm pretty sure ES is just one guy. From his website..."Expert Sleepers is currenty a one man operation - that man being me, Andrew Ostler (aka Os). I'm based in Letchworth, UK."

There is no way he has access to volume manufacturing that would allow him to compete with Behringer in terms of production costs.

3
thors-lab•

Oh! I didn’t know that at all. I assumed given the professionalism of the whole operation and how renowned their modules were that this was a multi person company. This definitely helps explain the price.

1
ouncesAndPounds•

anyone has access to volume manufacturing. There are plenty of Chinese companies that will manufacture your design and they don't care how big you are.

0
lm13700•

You cant really do price analysis of a module based on how much the individual components costs. Developing something like a ES8 is going to require significantly more R&D than say a simpler analog module and that would be factored into the cost.

2
thors-lab•

Of course, I agree with you. Please see my other comments in this thread! Sorry on mobile & don’t want to retype.

1
kalgoretrout•

How many precision reference circuits have you designed? Which high end calibration instruments do you possess? They can start at about $5-10k.

You’re massive,y underestimating the engineering that goes into this type of module. It’s more to the standards of scientific equipment than standard music gear.

2
thors-lab•

That’s true, but should theoretically be offset by scale. Being a semi-large vendor with a huge number of other modules, Expert Sleepers should only have to markup a relatively small amount to account for equipment and R&D.

What amazes me most is there’s no hobbyist level gear for this application. I do not intend to develop a precision audio interface whatsoever. But just as anyone can hack together a VCO, that while may not have incredible tracking, can be incredibly useful and affordable for the average musician, one should be able to put together a module like this.

Take the Behrinher UCA222. It’s $30 for two channels in and two out. While its not an amazing audio interface, it certainly gets the job done for hobbyist musicians. I would sincerely doubt it would cost an additional $520 to add a couple more channels and to extend the range to lower frequencies.

1
kalgoretrout•

What’s even the point of an inaccurate and noisy cv interface?

If it can’t keep time, and can’t spit out dependable pitch then it’s not an actual cv interface. It’s some sort of crude noise toy.

You keep making massive assumptions about how easy it is to make something like this, but the devil is in the details.

2
thors-lab•

Well, I suppose it’s a matter of priorities. In my own music, I actually enjoy a bit of noise and unpredictability. In fact, I frequently run audio through an extremely shitty 1966 reel to reel machine because I love that distortion.

Now that’s a pretty extreme example. Even putting together $3 ADC offers enough resolution to accurately track to +-5 cents. I know this because the module I’m currently working on does this. There are also a lot of monolithic USB audio chips that keep time for you.

Besides, I see the CV interface as a money saving tool in the first place. My only use for one would be to generate CV with virtual modules when I can’t afford their analog counterparts. If the CV module itself is extremely expensive, that defeats the purpose. The goal isn’t to make a shitty cv interface, it’s to make a cheap one, and if some sacrifices have to be made in terms of quality that’s something myself and I’m sure many others would be willing to pay.

1
Agawell•

any comparison of behringer to a eurorack manufacturer in terms of economies of scale is meaningless

behringer has an enormous product range, many of which will use similar components (resistors, capacitors, even basic ics like tl072 etc) so could buy them by the million - but they don't they manufacture them and sell them to smaller companies, for a profit

they'll also probably manufacture their pcbs etc in house

and all this is done in china where wages are incredibly low compared to, say the UK, where Os lives, or the US

most "large" eurorack manufacturers are doing runs of a few hundred, maybe less, of a module, smaller manufacturers are often in the 10s

plus most of them can't afford to have product recalls or bad runs, even if they are only very occasional, so want reliable and close in case there are issues and need to get a reputation - most eurorack manufacturers (including ES) have a great reputation - behringer has... a reputation

comparing everything else about any given behringer product with a eurorack module that does a similar function, but more of it, from a respected manufacturer is like trying to compare a 20 year old ford fiesta (tiny low power hatchback) with a brand new BMW i8 - they are both vehicles that will get you from A to B, only possibly in the case of the ford fiesta, but the experience is totally different

2
thors-lab•

Still though, the standard multiplier for even hobbyist level hardware manufacturing is 2.5x COGS. That would bring the ES-8 to a $220 COGS, a figure which I’m doubting for a mostly digital device with some ADCs and DACs.

1
versusentropy•

I use a presonus 8 channel ifc. It's DC coupled and goes close to 20Vpp, but it seemed to have trouble with some modules.

So I built a few buffered multiples. Works great now. I promised to publish everything, but was too busy. Hopefully I'll get to it over the holidays.

2
[deleted]•

[deleted]

1