VCV LFO triangle slope asymmetry - possible bug

I was testing out my new Venom quantizer - running a VCV LFO triangle wave through the quantizer in equi-likely mode to make sure that the timing between each interval being selected is consistent. I thought I had everything working. But as I did additional tests at a slow rate, I noticed notes being selected at one rate, and then suddenly the timing slowed down. The rate while the triangle was positive was faster than when it was negative. I started to panic. But then I switched to a Bogaudio LFO and everything worked as expected. Whew!

So why did my test fail with the VCV LFO?

Of course my test is dependent on the slope of the triangle wave being consistent. So I put together a patch demonstrating how Bogaudio and Surge LFOs are rock solid, but the VCV LFO and the VCV WT LFO are not. I set all LFOs to 0.03 Hz, attenuated the triangle waves to 50%, and passed that through the ML Quantizer. That quantizer fires a trigger every time the note changes. So the rate of triggers is a measure of the slope. I also set up a PUSH button to sync up all LFOs so they can be compared directly on a scope.

Bogaudio and Surge measured a consistent 108 BPM for my test. The VCV LFO and VCV WT LFO both register 108 while positive, but only 103 while negative!

Here is the patch: VCV LFO asymmetry.vcv (8.8 KB)

And here is a screen shot demonstrating the issue.

  • Red = Bogaudio LFO
  • Yellow = Surge XT LFO
  • Green = VCV LFO
  • Blue = VCV WT LFO

All four LFOs are reset near the beginning of the trace. Notice how all four remain in sync when the apex is reached, and the slopes are parallel up until 0 V is reached. Then in the negative region you can see a subtle change to the VCV slopes, and the VCV low points are delayed. You can also see the instantaneous computed BPM for the respective note changes in the Catronomix vcCLK modules.

It takes a long time for the Bogaudio and Surge LFOs to drift away from each other appreciably. But the VCV LFOs very quickly get out of sync with the others.

I’m not sure if this behavior is consistent. I thought I saw some times when the VCV LFOs behaved properly. Another time I thought the positive portion was slower than the bottom portion. But I don’t trust my memory. I did run a test at 0.04 Hz and for the limited time I watched it, the VCV LFOs were well behaved.

So be careful how you use the VCV LFOs. They may or may not meet your needs, depending on what you are trying to do.

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