Hey everyone

Was curious if anybody here has much experience with working with DC coupled audio interfaces. I have some modular gear and some sequencers that output MIDI that I was looking to convert the MIDI notes to CV and then output to the audio interfaces. Has anybody had any experience and success doing this?

Thanks in advance

@lo94 The old way to use audio outputs to control CV gear is to use a high frequency sine (highest your interface can put out) as a carrier for your CV, amplitude modulate the sine with what you really want and send it to [adc~]. Then you run it through a full wave rectifier and maybe some filtering and you have your CV. If you have some soldering skills you can make a two channel CV output that you can plug into your computer headphone jack for maybe $5, if not you can always go with simple passive rectifier and filter which is as easy as it get but you loose some of the signals amplitude in the process, if you have a VCA on that modular you use that too make that loss up or if your modular has a fullwave/halfwave rectifier and filter that can go down to DC than you can use those to do the lifting for you. It can be tricky to get well calibrated CVs this way, probably not too bad with a decent audio interface but if you don't need perfect key tracking than it is not a problem anyways. You can do very complex CV stuff this way on even simple analog synths with just a 1v/oct and expression input for CV, create all the modulation in pd or the like, sum and scale them then send them out, you can even piggy back gate and trigger signals on the audio signal by exploiting DC offset or just gating the CV itself if you are OK with the CV ceasing when the release cycle of the envelopes starts.

Let me knwow if you need more info, I kept it simple since I have no idea of your skill level.

Edit: if you want more info it would also be helpful to know your modulars CV/gate standards and what sort of CVs you want to send, plain modulators like LFO are much simpler than well calibrated key CV.

Edit 2: just remembered you said midi note information, not modulation. so needs to be calibrated. A bit more work but not much, very helpful to have access too a meter for calibration but can be done by ear if you do not.

Edit 3: we can probably use pd for calibration instead of a meter. Have not done this since the 90s, but it has me thinking and kind of makes me wish I still had some analog gear so I could play with this, will be much simpler in these days of modern interfaces, although the tendency for modern interfaces to have an analog volume control does complicate things some.

@oid
That's the spirit

Oh wow, thanks for the in depth response. I didn't know that about getting CV out through standard audio outputs. Luckily this seems to be quite a bit easier. I am running the Expert Sleepers ES-9 audio interface, and it seems to be as simple as simple sending a float value to the [dac~] output. I was able to just implement a simple algorithm to convert from MIDI note to V/Oct. I'll post the abstraction once I clean things up a bit, maybe someone will find it of use.

The tracking seems fairly accurate, I tested the full range (have Mordax Data, which has a voltage monitor). I haven't tested all the outputs yet though, so I'm sure some calibration may be necessary.

@EEight My record is 5 edits.

@lo94 I read your OP and AC coupled, DC coupled is easy and you found out. I was not quite awake yet when I responded, thankfully you figured it out before we had you building stuff.

FYI both the very old Echo AudioFire 4 as well as the MOTU 24ao output DC.

Oh duh, here's a list https://www.sweetwater.com/sweetcare/articles/which-audio-interfaces-are-dc-coupled/

Expert Sleepers i/o have a range of 20 Vpp, ideal for Eurorack.

@lacuna I see, that's why I keep hearing about those Expert Sleepers interfaces. My applications were so simple that +/- 6V range was plenty.