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AC Coupling CV control and Bitwig/Silent Way
MUFF WIGGLER Forum Index -> Expert Sleepers  
Author AC Coupling CV control and Bitwig/Silent Way
robinv
I am currently puzzling over AC Coupled CV control via both Bitwig and Silent Way. I think I understand it but i wanted to check with more knowledgeable people that i've actually grasped it. I understand the differences between DC and AC coupling. I did a video on Bitwig CV control over a DC Coupled interface - easy, no problems. But it has an "AC" button which should do the same thing as the Silent Way AC Encoder. Which i believe it does. However, the reality of using a regular audio interface is more difficult than the theory. I'm using an Avid Fastrack Duo. It seems to have a very low output in voltage terms. I run it through a Veils and with some curve tweaking i can get to +-5v. I then run it through a Disting set to ES-1 mode which extracts the DC voltage from the amplitude modulated AC coming out of Bitwig/Silent Way. At this point it goes through my scope and shows a rather fuzzy resultant LFO which has been half-way rectified. I can then modulate (or at least half-modulate) a VCF etc. Is this what i should expect to happen? If so does it really have any use since you can't get a full wave out of it?

I should stress that I am not looking for a solution to controlling modular from a DAW - I am making a video about using AC Coupled audio interfaces in modular in order to demo the Bitwig HW devices and Silent Way AC Encoder in the hope that it's helpful - there seems to be so little information out there on it - maybe no one does it - dunno....
os
Quote:
But it has an "AC" button which should do the same thing as the Silent Way AC Encoder.

I'm not so sure it does. Where does it say that?
robinv
os wrote:
Quote:
But it has an "AC" button which should do the same thing as the Silent Way AC Encoder.

I'm not so sure it does. Where does it say that?


Well, all I can tell you is that when you hit the AC button it amplitude modulates the output signal from the LFO, from which you can use the ES-1 to extract the LFO out of an AC coupled interface. I understand the SilentWay AC Encoder does this also. But this is why i'm asking smile
os
I see.

Well, with the AC Encoder and the ES-1 (or disting) you can certainly get a full bipolar LFO out, with no rectification. Perhaps Bitwig isn't handling the bipolar inputs gracefully.
robinv
os wrote:
I see.

Well, with the AC Encoder and the ES-1 (or disting) you can certainly get a full bipolar LFO out, with no rectification. Perhaps Bitwig isn't handling the bipolar inputs gracefully.


Ok - and feel free to treat me as an idiot - so a sine wave LFO through the AC Encoder, via audio interface, thru the Disting 4 in ES-1 mode should give me a sine wave at the other end? Not a half sine wave? Am I making any sense?
os
Yes, a sine wave, once properly trimmed.



[edit: sorry, thought that video had a sine wave output in it. But it does show the 'ES-1' outputting both positive and negative voltages.]
robinv
Ok - good information. I need to re-try a lot of things. I think i've also discovered that my audio interface is actually DC Coupled, which only confuses me further. I have spoken to Bitwig about it but they don't really have any helpful information on how the AC side works - other than to say it lets you use AC coupled audio interfaces. I get the theory, i'm just struggling to show it working in any sensible way. But if i can get SilentWay to do what i now it should then maybe I can make some progress. This is just with LFO's - on the notes side of things I could not get Bitwig's device to calibrate, whereas SilentWay voice does it without any trouble.

I really appreciate the input - i'll come back once i've cleared up some of the doubts and have a better idea of what does and doesnt work.
robinv
os wrote:
Yes, a sine wave, once properly trimmed.


Right - yes, sine wave confirmed from SilentWay. In terms of trimming, on my Disting 4 I don't really find a place where the LEDs are off - they are very dimmed but it switches from red to blue with the tiniest movement and i can't quite get between it. But that all works without any need for a VCA to boost the output from the interface.

In Bitwig the trim process with the Disting is a bit of a mess. No signal comes out unless you are moving the CV knob. If you then trim to having the knob at the maximum then your LFO can only pull down and do half a job. But once you have a signal going through you can trim it on the scope and you are getting red and blue out of the disting. HOWEVER, you don't get a sine wave, you get a reflected sine wave - so it looks like a bouncing ball on the scope, like the bottom half of the wave is reflected back up. Does that make sense?

What I've found then is that the Bitwig devices are not able to operate as bipolar. And they have a handy bipolar switch in the modulators, so once i've disabled that I can get proper sine waves out of the Disting - hooray!

So yeah, I think it is doing the same job as your AC Encoder, just not quite as elegantly smile
robinv
One last question - can you use the Disting to go the other way - take an LFO from my modular and route it through an AC coupled audio interface in order to modulate the software. Is that possible?
os
Yes, that's the ES-2 mode.

http://expert-sleepers.co.uk/distingalgorithms.html#es2

robinv
os wrote:
Yes, that's the ES-2 mode.


Aha!
robinv
Thanks for all the help - I hope i've represented Silent Way and the Disting appropriately.

os
Guinness ftw!
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