Audacity Forum

I notice loss of synchronization of tracks when applying plug-in effects. For instance when applying a "Chorus" effect to part of a vocal track, the section of the raw signal of the track receiving the effect gets pushed to the right, causing a delay, relative to the background music. Applying the "Pitch Shift" effect causes the raw signal to move leftward and play a fraction of a second earlier. By the time I have applied all the effects to the lead track, it is either longer or shorter than the background tracks that remain unchanged. The asynchronization is intolerable. But I am able to correct the problem by cutting out and adding silent parts of the track. But this labor is very undesirable. Maybe the Nyquist plugins are not quite compatible with Audacity, or the Beta version (1.3.12) of Audacity has a bug. Is the problem I describe also inherent in v1.2.6? Any idea how we can get around this problem?

You are the first to report anything like this. I did a few quick tests with a 100 Hz tone, and did notice something like what you are describing, however it was a matter of a couple of samples. Change Pitch will necessarily throw out or add samples to accomplish its task. The Chorus effect (which is not included with Audacity) probably includes filters and pitch shifters to build the effect. Any equalization will involve phase shifts.

Can you give an example of a workflow (that only involves effects included with the standard distribution of 1.3.12) that causes audible desynchronization of tracks? Be sure to include the length of the track.

Does the effected track slowly drift out of sync, or is it apparent at the start of the track?

-- Bill

Hi Bill,

Here are the effects I used and their impact on timing:

Resident "Change Pitch" moves the raw signal significantly leftward, really noticeable when you zoom in.

Kjaerhus Audio: Classic Chorus causes audio drift: the larger the section effected, the further to the right the raw signal is shifted. I highlighted a section and applied the effect, noticing that the beginning is not shifted.

Equalization, Amplify, Normalize, Fade In/Out, GVerb, and Multivoice Chorus did not cause asynchrony in my test.

I hope this helps.
Regards

I'm not surprised that Change Pitch had that effect. See this page: http://wiki.audacityteam.org/index.php?title=SoundTouch

I can't speak for the "Classic Chorus" effect, but I note that Steve Harris' Multivoice Chorus LADSPA effect does not cause the problem.

Try the "Sliding Time Scale/Pitch Shift" effect with the same values for initial and final pitch shift. It is considerably slower, but does not shift the audio.

-- Bill

Hi Bill,

Yep, the "Sliding Time Scale/Pitch Shift" does not cause adio drift; but unfortunately it adds a tonal change, similar to a flanger, with or without dynamic transient sharpening. Looks like I'll have to stick with the "Change Pitch" option and correct the inherent problem with the "Change Speed" or Change Tempo" tool. Cutting & pasting silence to compensate the drift seems to work OK, albeit a bit of a chore.

Yeah, too bad application of the Kjaerhus Audio Clasic Chorus effect causes the section effected to run with a tempo delay, since for me this plug-in offers a far better chorus effect than the Multivoice one.

Regards
Djard