Module to Convert Modulation Signal to Audio and Back
Nikolozi
Samu had a great suggestion:
> One thing I've been playing around with in Drambo lately is processing modulation signals like they would be audio and using them to modulate parameters. (various pulse thru a filtered delay/echo as one example).
> As for Mela a module that converts modulation signal to audio and back could be something to add at some point?
Some thoughts:
- I imagine it will be similar to the Audio-to-Mod modulator module, except it will have a sublane and a modulatable dial.
- The sublane will not receive any input and won't merge its output.
- It will have a dial/slider that the user will modulate.
- The modulation signal then will be sent to the sublane as input.
- The user will have audio processors in the sublane to transform the modulation signal.
- The processed audio will be converted back to the modulation signal.
- There probably will be a Depth parameter.
- Visualiser of the resulting modulation signal will also be useful.
Nikolozi
While exploring various related features, I realised this is already possible.
Here's how:
- Create an empty lane.
- Insert a Rectifier module followed by an Audio-to-Mod module.
- Modulate the DC Offset parameter with any modulation signal. At this point, the Rectifier's output audio signal is the same as the modulation signal (maybe slightly different amplitude depending on the modulation amount).
- Audio-to-Mod will receive this signal. So, modulate the desired target parameter using the Audio-to-Mod. At this point, your original modulation signal is modulating the desired parameter.
- Now you can insert any module between these 2 modules to transform the modulation signal using audio processors. In the screenshot, I'm adding a delay effect to the modulation signal.
As a bonus, both Rectifier and Audio-to-Mod support polyphonic signals, which means that unless the audio processors used collapse Poly to Audio, the resulting modulation signal will be polyphonic. Just don't forget to insert MIDI-to-Poly before the Rectifier, feeding it the same MIDI signal as your target modules.
I think this will serve as a good experimentation playground. The main issue is that currently, audio processors aren't optimised for low-frequency signals. For example, filter cutoff frequencies go only as low as 19.5Hz, so you can't easily take a square LFO and convert it to a squiggly one.
Nikolozi
Jon Diercks tagging you, because I think you might also be interested in this. Also, I haven't forgotten about the Slew module (still thinking about it). And it's kind of possible with the above technique, where you would take the Rectifier's output and feed it into the Envelope Generator (you wouldn't even need the Audio-to-Mod). The main downside is that you wouldn't be able to reach your 30-60s long ramps, as Envelope Generator's max Attack/Release values are much lower.
Jon Diercks
Nikolozi - Thanks, and yes, I've been at least partway down that road experimenting with envelopes etc. to approximate slew behavior. I hadn't really understood Rectifier until recently when you explained it to me. This is good foundational stuff, and will be useful to have in the toolbox for future projects. And thanks for continuing to keep things like a Slew module on your radar. :-) Those long ramps will be great for ambient music.
I also wasn't aware that the LP filters only go down to 19.5Hz ... that explains some things I've seen on scope output. So what's the "right" way to get rid of frequencies below that? I guess add an HP or BP with just those lows notched out?
Nikolozi
Jon Diercks Regarding, as to why filter cutoff frequencies go only as low as 19.5Hz, and in fact, most freq parameters in Mela have that, is that because in the synth / audio-fx world, filters tend to have the 20hz-20kHz range by default. Because usually, values outside that aren't useful. So, I wanted to pick a range that was as close as possible to that, plus span exactly 10 octaves. So, I came up with [19.5, 19968], 19968 = 19.5 x 10^2. This allows things like Key Track and Pitch Follower to modulate frequency parameters in such a way that the frequency parameter follows the pitch value exactly (or is shifted a few octaves).
Now, if you are dealing with modulation signals, you might want to have lower cutoff frequencies, and the reason is, say you have an 8Hz square wave modulation signal (that you converted to audio), with a filter with say 2Hz cutoff will convert your square into a squiggly one like the screenshot. And when modulating a parameter, it will sound cool (hopefully). HP and BP with the same freq range won't be of help. We just need an LP filter with a range that can go much lower than 19.5Hz. So maybe we'll have something specifically optimised for modulation signals. I'll have to think about it.
Thinking out loud here, maybe the hypothetical Mod-to-Audio will have a built-in 1-pole / 2-pole lowpass filter.
Jon Diercks
Nikolozi, ah, ok, that makes sense.
Sascha Brossmann
Great suggestion – that would give Mela full Eurorack powers.