VAP Synth: pop and clicks related to square wave LFO modulation

Bug Description

I discovered a (VAP) synth patch settings that cause clicky and poppy noises and other distortions. The particular patch settings I used if I switch the Filter Type to other ones the problem still remains on what seems like each of them, but the amount of the issue varies a lot. In this case I noticed the problem goes away if I switch LFO 1 - waveform from square to something else like Triangle, or Random S&H as two examples. A quick test seems to indicate all filter types work fine after doing that. Check the other first related link for a recorded video example with another synth patch that sounds similar.

Reproduction Steps

  1. Sequence any pattern with the included “$ Pops and click.patch”
  2. Press play and notice the distortions and clicky and poppy type noises.


Always with the given sound patch file I made.

Found in

go to Config > Firmware page on your device and copy version / build numbers below

  • Version: [1.0.1 beta]
  • Build: [1376


$ Pops and (580 Bytes)]

Other synth sound issues possibly related they all produce similar sound issue

Thanks for sharing your .patch. Gonna load it up in a bit and will report my finding.

Hey @radfaraf, thanks for logging your bug. Something I’d like you to try to see if you can replicate what I’m experiencing.
Having your patch loaded and some notes playing to hear the gliches

  1. Go into the VAP engine assigned to your patch.
  2. Go into edit patch and scroll all the way down to the -----Modulation----- secition of the patch editor.
    You should see that your Src 1 is assigned to LFO 1 with Amt 1 set at 200%
  3. Select the Amt 1 parameter currently set at 200% and bring the amount down. Does the glitching go away for you when you go lower than about 150%?

I’m gathering that this is part of Polyend releasing the firmware with the patch editor in a public beta form that is not fully optimized for a full firmware release. I’m seeing all of the Amt destinations in the Mod matrix going up to 400% and that for me looks more like a testing range rather than something that would be implemented in a more stable non-beta firmware. Anything over 100% seems a bit bizarre on a mod matrix level unless each of the sources had their own amount level which is not the case in the synth engine.

I see if I put all the matrix stuff there to 100% for that sound instead of 3 of them I set to 200% the issue still occurs, but way less of it, and on most filters not at all. I have no idea why it lets those big values either, but since it lets me I did it! Plus it sounded like it was helping the sound up until some point till it didn’t :smiley:

Still hearing it a bit on LP OB 24dB and LP OB 12dB for that sound. With the the 3 modulation sources all set to 100%. 150% seems too high hear a lot more of it at that level even with just 1 modulation source set to 150% and the rest 100%

Thanks for sharing your findings If you have the time to go through the specific steps I outlined previously it would help quite a bit. I’m pretty sure the problem is specific to the modulation on Src 1 going past a certain threshold. Would love to know if keeping your original patch as it is and only decreasing the Amt 1 of Src 1 lower than 150% removes those glitches for you.

It seems like you’re thinking I am talking about something else, but we are talking about the same thing (I did what you said). I did only the one mentioned at first and since it didn’t work completely I did the others, and all 3 isn’t even enough to fix it though it is hugely better.

Sorry, maybe I’m misunderstanding somewhere;

I’m having trouble to read where in this txt you’re going through the step by step that I described. Sorry if I am misunderstanding something.

Could you share that patch with your adjustments that are better but don’t work completely?

$Pops and (577 Bytes)
Here’s the file I changed all 3 modulation settings that were at 200% to 100% in this one. Still hear the issue, but a lot less.

Cheers! That helped alot and is concurrent with my findings.

If you go into the -----Filter------ section and bring down your cutoff frequency, I think your problems should be solved.

The current synth engine seems to have an issue to deal with values above the max. Cutoff Frequency. In your patches, the Cutoff is almost fully open, and sending high levels of modulation that brings it much higher than it’s max setting, and I think that is what is causing the erratic behaviour.

For the things mentioned in this comment I setup my notes just using 4 notes equally spaced with note length set to 3.00. Then I set them to minor chord using the “sample start” knob button. Using chords makes the issue a bit worse because more notes at the same time.

Still running into the issue with much lower cutoff frequency, for instance I still get it with 3.10kHz (max is 19.3kHz) and with LP OB 12dB. Even quite a bit lower, but it does become really hard to tell at some point where exactly it stops because the lower the cutoff the less of the issue is heard.

Still using the above note settings:
24dB filters also make it trigger more easily.
I also see for instance if I change Filter type to LP MG 24dB it will keep sounding extremely bad even at the lowest of 20Hz on the filter cutoff and with both chords and no chords being used. This one actually seems to get much better at a real high cutoff. Other 24dB filters also seem to need higher cutoff and not lower.

Hi @radfaraf , thanks for reporting this bug with so much detail. We’re sorry you’re having issues with our products. We’ll let you know if we can improve this behavior and fine tune the ranges to avoid these more extreme settings. Thank for your support!