LFOs getting out of sync!

[super-manis]

System Information

Ubuntu 24.04

LMMS Version(s)

1.3.0-alpha.1.627

Most Recent Working Version

All nightlies with tempo sync function

Bug Summary

There is an option for syncing LFOs to the tempo of the song. What it does is actually to calculate an approximate value for the LFO and put it in the frequency knob so it completes a period every 1 or 2 beats let's say. This approach however sometimes leads in cases where the value of the LFO frequency doesn't match the BPM of the song thus getting out of sync after a while.

Expected Behaviour

The LFO to stay in sync with the global tempo

Steps To Reproduce

In order to test this you can try using a saw-wave as sidechain for a volume knob. I personally tried with the tempo set to 128 BPM and for the frequency to be synced every quarter of a bar. After like 24 bars it started drifting. The more time i gave it the more it lost synchronization with the tempo.

What i would suggest is for the LFO to somehow get triggered to reset itself every 4 or 8 bars so the effects of this approach get minimized. Solving this issue would give LMMS a really strong LFO tool that could be used to sidechain various parameters with complete control just like tools like (if i'm not mistaken) XFer's LFO Tool and Image-Line's Gross beat all in sync with the global tempo.

I ran a test in which i sidechained a sinewave and added a Click every beat so difference can be seen. The first picture is the beginning. The second is the end after 6 minutes:

Screenshots

[softrabbit]

Could be the same as #2047, a situation where floats aren't precise enough. Switching to doubles would be a pretty small fix, compared to adding some kind of sync. Probably worth a shot.