Moog Music Forum

I noticed something with a bass patch I made. After so many bars of the bass pattern playing (sequenced via Logic X) the bass frequencies begin to roll off, like there's an LFO doing a slow HP cutoff starting at 20Hz and ending around 200Hz (rough estimate) then it cycles around to playing the full sound again. All my LFOs are off on hardware and in the Editor AU. From my understanding this shouldn't really even be possible as the Minitaur on has a LP filter. Anyways, that's what it sounds like. It could be a VCF LFO AMT leak, I dunno.

If it would be an LFO leak to the VCF, it would be a lowpass filtering you would here, as there is no highpass in the Minitaur. So this is not a possible explanation of what might be happening.

So I guess you got some real slow beating between the two oscillators that give you the audio impression of a highpass filtering by canceling each other during the beating cycles.

Check with one oscillator muted by changing its level in the Minitaur mixer full CCW to zero. Does it still happen?

And also be sure there are no MIDI CCs are going to the Minitaur by mistake (other tracks sending on the very same MIDI channel?). So mute all other channels on Logic for this test.

I'll do some further tests with your recommendation. It might be as you said. I'm pretty sure I had both VCOs at zero in fine tune and beat parameters, but will test again.

Even with detune and beating to zero there will be a slow beating due to analog drift of the oscillators. Even on such stabil oscillators as used on the Minitaur and later Moog synths.
On the good old vintage analogs here you get beating if detune is set to zero for sure if the temperature in the room changes about 1 degree Fahrenheit or Celsius.

I guess what made me really notice was that it was quite pronounced. The low end got sucked right out and the amplitude dropped.

So at the moment it seems it might have been the wave cancellation due to some beating between VCOs though I figure there shouldn't be any beating with VCO 2 FREQ Knob and VCO Beat FREQ knobs at center.

Also wanted to ask if the LFO rate knob doesn't go to full off position when turned all the way down? The VCF LFO AMT and the VCO LFO AMT will induce the LFO even when Rate knob is all the way left.

Holiday101 wrote:So at the moment it seems it might have been the wave cancellation due to some beating between VCOs though I figure there shouldn't be any beating with VCO 2 FREQ Knob and VCO Beat FREQ knobs at center.

There will be no way to stop beating perfectly. Remember these oscillators are analog and might drift a tiny bit. And it takes only real low changes in the frequency to get some beating and canceling. This is absolute normal. And the Minitaur is one of the very pitch stable synths I own. So it isn't its fault. It is just normal for analog synths-

Also wanted to ask if the LFO rate knob doesn't go to full off position when turned all the way down? The VCF LFO AMT and the VCO LFO AMT will induce the LFO even when Rate knob is all the way left.

The rate does NOT change the modulation amount, but the frequency. And it is absolute normal for all synth, including DSP digital synth, to have modulation even at the lowest available LFO rate.
But maybe you confuse amount with rate?
If the VCO LFO AMT and the VCF LFO AMT are set to zero you should get no modulation by the LFO. Be sure not to use relative knob mode without swiping through the whole range of a knob, as the relative mode will not show the real values on the hardware scales.

You might also try turning on the Note Sync function (I believe only adjustable from the computer editor). It will sync the phase of the two oscillators at the beginning of each note, so at least they should start in sync with each other.