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Joined: 04/15/2017 - 15:13
PadSynth beating/wobbling sound

I've recently stumbled upon Caustic, and overall I'm very impressed, most of all by the user interface that's really fun to play with. The tutorial videos are also really great and help one get productive in no time.

Now I'm trying to create an ambient style track, and the thing I'm fighting with at the moment is a rather annoying "wobbling" effect audible in many PadSynth configurations, as if from an LFO controlling the volume. This is pretty easy to reproduce: Create a new PadSynth, go to harmonic table 1, draw in a single harmonic. Depending on the value of the (yellow) bandwidth bar, the volume will oscillate at different frequencies. I've compared this with the PADsynth in Yoshimi (a fork of ZynAddSubFx), which seems to be based on the same algorithm; there, the same effect is also noticeable, but less pronounced, and less annoying.

After skimming the description of the algorithm, my best guess as to what is happening is this: Mixing two similar frequencies will always produce a beat due to interference, but as the ZynAddSubFx implementation shows, with more than two frequencies the effect can be made to cancel out to some extent. The regularity and reproducibility of the beat patterns in Caustic suggests that either the phases of the frequencies belonging to harmonic are not randomized properly, or there are too few frequencies per harmonic (maybe because the spectrum array fed into the FFT is too small). In any case, this should be relatively easy to fix (possibly by adding an HQ switch if the fix is computationally too challenging for some devices).

JHSound's picture
Joined: 06/04/2015 - 11:21
For what it's worth, from

For what it's worth, from someone much less educated on the programming aspects, I've always noticed a slight pulsing on padsynth sounds. Sometimes it is pleasing if it fits with what you are doing but sometimes is too noticeable.

nitro27's picture
Joined: 10/11/2015 - 18:27
It seems to me that

It seems to me that randomizing the individual harmonic phases would succeed in nothing more that randomizing the phase of the beat frequency. I'm probably wrong about that.

Note that Caustic's PADSynth is an absurdly light synthesizer, my old cheap phone can handle 11 of them at full bore at once, but even then it's one of Caustic's most taxing synths. You're probably right about the frequencies-per-harmonic thing, or is it harmonics-per-note?

Sidebar: I played with Yoshimi a bit to see if I could compare CPU loads and such, (I can't,) and dang that's a good program! Why haven't I been using that?

I make Chillout Electronic Music, and sometimes Ambient. http://floatingbeyond.tk

Joined: 04/15/2017 - 15:13
@JHSound: Yes, whether it's

@JHSound: Yes, whether it's an issue or a feature depends on the sound you're trying to achieve. Alas, I wasn't able to get the effect I had in mind, neither with Caustic nor with Yoshimi. Probably more for lack of skill than due to software limitations. For what it's worth, I went with the Organ Synth instead, which gives the track a different flavor, but does feel quite natural.


@nitro27: You're right for the case of two frequencies - in that case only the phase of the beat frequency varies. In general though the amplitude of the beat will vary as well. Here's an example; the blue curve shows three frequencies in phase, the red one the same frequencies with phase variations: