Zebrify strange amp mod behavior.

[Ah_Dziz]

Hi there. I've been using zebrify as a midi controlled effect a while lot recently (mostly for mts-esp compatible FM, filters, and comb resonators) and I've been doing more complex chains including multiple separate "lanes" that can be switched or faded between via midi (or any other mod source ), when, previously, i had generally just made a big old static mess of processing or maybe crossfaded chains that would all output through a single "VCA".

Anyway I noticed that, when an amp is modulated into negative territory, the signal comes back. I don't know if the new "negative signal" is actually phase reversed, but this is not generally the expected behavior for VCAs that aren't being used for sub audio frequency modulation.

To be clear, if I want VCA 1 to go to silence when cc1 is at it's maximum and the level of VCA 1 is set to 20, then I have to set the mod level from cc1 to -20 exactly. Any setting from 0 to -19.999999999 will leave some residual audible signal, and any setting from -21 to -10000000 will gradually add audible signal back in. I first noticed this with some envelope based turning down one VCA and another VCA up via the envelope follower and it took me a while to realize what was going on.

As I said you top, it's not the biggest deal or anything but it's not what I've come to expect from plug-in amplifier sections that aren't set up as audio rate amplitude modulators. So is this the expected/ intentional behavior? Is the "negative signal" actually reversed in it's polarity? If the signal is polarity reversed is there any chance of adding a "feedback" module with a unit delay or something that could make cool use of this polarity switching? If not is there anyway this behavior could maybe be switched off so that the amplitude just bottoms out at dead silent?

Thanks,
JJ

[Ah_Dziz]

Hello again,

Is "negative" ( meaning -60 mod level in the matrix while the volume is set to 50) modulation of the volume parameters in each "lane" of zebrify supposed to invert the audio and bring it back into the realm of audible sound? It appears that this is how zebrify works (might not really be inverting the waveform) and the inputs on the comb module, for instance, do behave this way. I'm returning to a track I was working on when I noticed that I had exactly cancel out the "volume" setting when modulating these levels.

Thanks
JJ

[Chris-S]

Yes, this is how some of the modern u-he stuff is working. I have the same issue in Hive.

[Ah_Dziz]

Okay. It's not crazy to work around. Just wanted to make sure it was on purpose. Is the "negative volume" actually phase inverted? That could be useful I didn't bother to measure it as it wasn't related to what I was doing.

Thanks
JJ

[NAD]

You can rectify/normalize your modwheel input using a modulation mapper.

[Howard]

Is the "negative volume" actually phase inverted?

That was easy enough to check using a sawtooth, Zebrify and an oscilloscope.
Answer: Yes!

[Ah_Dziz]

Thanks Howard. I'm lazy it turns out.

[Chris-S]

In Hive it's inverted. Can be used to get a inversed sawtooth wave.

I'm not a fan of this behaviour (is any hardware synth doing this?) ...

[Ah_Dziz]

It's standard behavior for an analog bipolar vca. For modular setups it's kind of a given that multiplying a signal by a negative number will result in an inverted signal. Something to keep in mind with things like reaktor and pure data. In my experience most synth s with a single main output vca do not behave like this which is why I was a bit confused with zebrify.

Usually a module that's bipolar will have a bipolar level control to go with the bipolar vca. It's simple to work around in every case I can think of. Just unexpected.