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Beat is off in final .wav mixdown


I'm using Qtractor and Qt 5.12.8

My song is finished and I'm happy with the way it sounds when I play it in Qtractor.
I mixed down my song to a single .wav file, from Edit -> Track -> Export Tracks -> Audio.

It finishes saving the .wav file.

However, when I play the .wav file, the song does not go from one bar to the next smoothly, there is a slight (but noticeable) pause, then the next beat starts.

If I can describe the beat as text, it should sound like this:
beat beat beat beat | beat beat beat beat | beat beat beat beat | ...........

But it sounds like this:
beat beat beat beat | (0.3 second pause) | beat beat beat beat | (0.3 second pause) | beat beat........

It sounds perfect in Qtractor, just not when it's mixed down.
I know I can bounce the playback to one track and use that to export to wav but I would prefer to mix it down to a .wav directly from the Edit menu.

Any ideas why the beat is off in the final .wav but not in Qtractor?


rncbc's picture

hi, indeed it's quite strange...

without any further details it's hard if not impossible to investigate on this ...

can you just put up a minimal short example session file, preferably in archive/zip bundle format (save as .qtz) from which an audio export/mixdown results in the same off beats or pauses? a single track over a couple of bars length would be enough.



I've attached a short example session file which plays fine in Qtractor (no pauses between bars), but when it's mixed-down, there is a noticeable pause between bars.


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rncbc's picture

hi, thanks for the short example session file.

tried to export (Track > Export Tracks > Audio...) in many occasions and settings (sample-rates 44k1 and 48k; buffer-sizes, 128..1024) and the results were all as expected: i hear no pause or delay on the beginning of each bar whatsoever, or so i believe :)

even playing both tracks in unison, the MIDI track ("Drum") and the audio exported one ("export-1"), i don't find or hear a significant difference, but a slight phasing effect due to superimposing stereo reverbs... besides, it all sounds with no pauses or gaps when played simultaneously (nor soloed).

for visual evidence, i've added here the simple screenshot:

any insights on where the problem is hiding perhaps? it could be my musical/rhythmic skills (or lack thereof) that are at stake here :)


I did some more testing and I discovered something.
The mix-down pause issue goes away when I lower the Latency (specifically Frames/period) in QjackCtl.

For example, my Latency was set to 46.4 msec when the pause problem was happening (screenshot png attached).
The Frames/Period was set to 2048.

I changed the Frames/period to 512, which brought the latency down to 11.6 msec.
After mixing down using that setting, the pause issue went away.

So it all had to do with the latency (11.6 msec was good, 46.4 msec was causing the pauses)

The reason I had it set to 46.4 msec (2048) was so that the playback in Qtractor would not show XRUN. I experienced no XRUNs at 2048, but lowering it to 11.6 msec (512) causes XRUNs during Qtractor playback. So it seems that when I'm ready to mix-down, I must lower it to 11.6 msec (512).

Thank you!

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rncbc's picture

weird i have not (nit)picked on those scenarios when testing with different sample-rate and frame buffer-sizes...

let's try some other thing: disable(deactivate) all calf plugins thereafter the avldrums.lv2 plugin and check whether it makes a difference... fwiw. i'm suspecting the Calf compressor is the culprit there, but please check it out



I did more tests as you suggested. I actually ended up removing all the plugins from the track except for the main instrument itself. However, that did not make any difference.

I've attached a screenshot that shows the MIDI and the mixed-down Audio - you can see that the 3rd beat starts a little later than the first 2 beats.

So removing the Calf plugin(s) did not make any difference here. This was done with Frames/period set to 2048 (46.4 msec).
If I change it to Frames/Period 512 (11.6 msec), it will sound normal.


File attachments: 
rncbc's picture

interesting, so it seems avldrums.lv2 is at the stake then...

can you check with some other instrument plugin, any other but avldrums.lv2 ? maybe yours truly drumkv1? (sure you'll have to load each drum sample before hand, but well, as the french saying, one doesn't make omelets without breaking some eggs, do we?:)


I changed the instrument to MDA Piano and it has similar results - I can still hear a delay after each bar.
I have drumkv1 (thank you for all your plugins and also Qtractor!), however I don't have samples for drumkv1 yet.

rncbc's picture

oh-kay.. you might have a point here... after dwelling with 2K+ buffer-sizes the early note delay is then noticeable and it gets weirder, the delay seems to go away towards the end of each bar...

sure this deserves a deeper investigation ntl. until it gets squared out, when and if it gets there, please keep those buffer-sizes shorter as possible: 128 frames is, has been, an all-round and pretty much ideal figure. trust me ;)

thank you a lot for your kind perseverance

ps. having xruns @512 is not really acceptable; please do tune-up your linux system : for over a decade now that is plain possible to sustain a 128frame/buffer with absolute-zero xruns. you'll just have to tweak your system here and there once, trust me again :)

pps. check this out:, and follow the hints from there... ;)

I trust your advice, I'm still relatively new at using Linux for creating music. I thought I already learned what I needed to know (example: using a low-latency kernal, using an audio interface device, not built-in sound card etc.), but I clearly have more things I need to learn. I will check out the link you shared. Thank you for your time and advice.


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