I’ve noticed the output of some LFO’s at slow speeds is slightly “steppy” and others are completely smooth, or smooth enough for my purposes anyway.
For example in “slow” mode the Bogaudio LFO is too “steppy” for my patch, and the NYSTHI LFO Multiphase and Frozen Wasteland Super Slow LFO are both super smooth and quite good for this particular patch.
Can someone explain why this is how it is with some modules, and also is there a way to tell which modules will be high enough resolution for this patch I’m working on without trying them all.
In my LFN I put a one pole lowpass on the output just to avoid this kind of thing. It’s not something that most people know or care about. And there is no easy way to find modules that are “good” vs ones that “have issues”. It is discouraged here to say anything negative about a free module.
As far as this issue, some people run LFO at full audio rate, which will not have this problem, but will use way too much CPU. Some ppl run at reduced same rate to save the CPU, but then run the risk of jaggies on the output like you are complaining about.
My LFN runs at an internal sample rate of 400, then uses the lowpass running at full audio rate to filter out jaggies.
Thanks. I don’t think I was saying anything negative, I made sure to say “for my purposes” or “for this patch.” I LOVE the module in question by Bog, I usually use it first before any other module, its in all my patches, but in this particular patch, I began exploring other similar modules for the first time pretty much, was happy to find some that went high enough res at slow enough rates. I mean this is painfully slow… pretty unique use case I would imagine. Will scope LFN now…
Here’s a way to “measure” that. here I took two LFOs, set them both to .01 hz, then ran them through DC blockers set at 50hz. You can see both on the scope and the specturm analyzer that the VCV LFO is smooth, but the bogaudio has jaggies. You might try logging a bug with bogaudio - they have been pretty good in the past with fixing things. And, that’s what this is, a bug.
Ha! I noticed that inadvertently with the stepping on Bogaudio. I was using 8FO to modulate a few different things in an effects patch, and got a really crazy sound with Glitch FX’s Satanaut. I couldn’t work out how it was making that sound, then I realised it was a stepped output from 8FO in slow mode. I actually really like it for some effects, it was like a really slow arpeggio.
However, wouldn’t a simple slew limiter fix this if you want a smooth output? Or am I missing something?
Yes, simple slew limiter would fix it. Which is very close the the one pole low pass filter I mentioned. But in any case it’s it bug. Like many bugs, it can be worked around. If you actually wanted that stepped sound that would be an unusual case - then you’d probably step it yourself with a S/H?
I tested a few different LFO’s and it’s only the Bogaudio LFO’s that has harmonics on the sine output, and this surprised me. Then I looked in the right-click menu of the LLFO, and there you have two settings for “Output sampling” and “Smoothening” for deliberately changing the waveshape, to be more jagged or more smooth. I think what happened here is, that all his LFO’s has that circuit, and it’s in the signal path all the time, having the side effect of producing noise at the neutral setting where it should be clean. I’d imagine he just forgot a (IF) check in the code for the neutral case where this circuit should be decoupled.
I created a thread a couple weeks ago about stuttering happening with my LFOs, particularly the super slow LFO from frozen wasteland. I was modulating the super slow LFO with a bog audio LFO but then to try and troubleshoot why the stuttering was happening, I remember removing the bog audio LFO from the patch and the super slow LFO was the only other one left and it was still stuttering. Could something like this be happening because of a bog audio LFO even after you remove it from a patch?
oh - I never notice the smoothing control. I guess in the normal mode the sin output is smooth anyway, so it’s fine that it defaults to off. But in the slow mode it should be on. At least for the “smooth” outputs. I think the problem here is that this LFO has too many options. Too many for me, anyway!
For the record, 8FO does have a smoothing control – it’s the knob marked SMTH (panel space is always a thing). Internally it’s a slew limiter, same as in my other LFOs.
For you DSP guys, the cause here is: all my sine oscillators, LF or otherwise, use a wavetable. I did without interpolation, back in the day, to save CPU, thinking if the table is big enough (here, 4096 samples) it’d be fine. At audio rates, there are some extra harmonics, but I find those generally pleasing, as in FM-OP. But yep, doesn’t work well for LFOs. Enabling interpolation fixes it.