Moog Music Forum

I just got a used LP SE from Guitar Center and there's a few things I've noticed with it, and wanted to know if thats normal , or if it could be faulty and I should return it while I still have a chance.

When I program a basic bass patch, consisting of pretty much just a triangle wave with 1 osc and all other settings flat (but for some of the filter rolled off), I randomly hear this click/pop sound on the attack of some notes. Similar to that of vinyl crackle, but just 1 single click each time (as opposed to multiple clicks of vinyl).

I know when you get really low on the keyboard, the notes become inaudible it can just sound like clicks. But this occurs higher up in the bass register where you normally play basslines in the octaves like you would on a bass guitar.



Also, if I bring in the 2nd osc with the same exact settings, to beef up the bass sound, I notice this weird thing where it seems like the filter is slowly opening and closing the longer I play. Like I play a 2 bar bassline and it starts out at the bassy cutoff point that I set, but then by the 2nd bar I can tell the high freq start to come back in and the fat bass kind of disappears. And then slowly comes back in, and repeats in a cycle like that as long as I keep playing.

Is there some kind of setting inh the Master section that auto sweeps the filter or something? It only happens when I use 2 osc together, and also only seems to happen on bass sounds. I don't notice it on leads when using 2 osc. I also don't hear the clicks/pops on leads.

Is this all just some quirks of analog osc, or could there be some issue with this synth?

For the first issue: Its probably your envelopes. With the attack and decay all the way counterclockwise, it doesnt mean the attack/decay time is zero, just very very fast which can manifest itself as a very short click when you hit a key. I find that annoying also, but you can turn the attack up a very small amount and see if it gets better or goes away.

For the second issue, this sounds like oscillator beating. Try turning the osc2 freq knob a very small amount (you wont see any LED indication change for very small movements but you can hear it) (or better yet, use the fine tune menu feature) to see if the rate of sweep gets faster. Actually, you can try this by playing a low sustaining note and listen to the phasing. Then play another higher note and see if the speed increases. If either of these make it happen faster, it is normal oscillator beating. Unfortunately on the LP you cant do anything about it. The Sub Phatty and Minitaur have OS settings that you can control the Osc beating frequency and make it more predictable. Basically both OSC are free running and dont sync to each other (unless the OSC sync button is active). So when you mix them together you get phase cancellation and reinforcements as they go in and out of phase with each other.

Hope that helps.

if it's a single click every few notes, what you are hearing is indeed an analog quirk... namely, the phase of the oscillator waveform is not fixed relative to the volume envelope. The oscillator is running freely with no reset and then when you play a note it triggers the volume envelope which opens up the VCA.
The reason you only get a pop on some notes is that on some notes the envelope happens to hit when the VCO is at the peak or trough of its waveform, and other times the envelope starts right when the VCO waveform is crossing zero.
For low bass notes with fast attack, the VCO signal is moving a lot slower than the envelope is, so it makes a big sonic different whether the envelope lines up with the peaks or zeroes of the VCO.

And yes the thing that sounds like a slow filter opening and closing when you have two VCOs playing the same note... that is slow beating or phasing between free-running analog oscillator... it's something that software programmers have to try very hard to emulate correctly.

One option is just to enjoy it because it's the sound of your oscillators being alive... if you want to minimize or work with this effect, here are some tips:
1) the closer the two oscillators are to being the same level in amplitude (and same wave shape), the stronger the effect will be. So you can try putting one oscillator at half the level of the other, and set them to different wave shapes, and you'll have less pronounced beating and cancellation...
2) go to Master Menu, Precision Mode, press the Osc2 Frequency button and you can use the Value knob to set VCO2 frequency in precise increments, until the phasing between oscillators is as slow as possible.
3) you can use oscillator 2 to reinforce the strength of your bass sound without any beating, by turning on osc2 sync. If osc2 is only slightly higher pitch than osc1, then you won't have the traditional edgy sync sound, you'll just have a stronger fundamental. Again play with relative levels and wave shapes for best results.

happy tweaking!

Thanks guys!

I'm relieved to hear that its normal behavior. I actually don't even mind the clicks because the bass sounds so good! I just wanted to make sure nothing was wrong with it.

And yeah the phasing/beating is exactly what it sounds like with the 2 oscs together. I agree, there's something cool about the randomness of it, and I prefer it for leads, but I like having the option of a more consistent bass tone too in some instances. In those cases, I'll just use 1 osc or try some of those tips you listed for getting them closer together.

Thanks for all the help. This Little Phatty sounds amazing!

A FAR better explanation Amos...

Haha, I guess thats why you work at Moog and not me... Cheers