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Strange issues after bouncing

Hi! I'm using Qtractor 0.9.5

For a while, in the last months, I didn't "bounce" anything.
Yesterday, after bouncing some tracks (Export -> All tracks) I got a final audio file with 2 strange issues:

1- In some points the track clips, even if while listening to all tracks together I dind't hear any clip (later, I listened to the song many times), and paying attention to che level meter on the Master bus, I'm quite sure that volume never exceeds. So I put a Limiter on master bus and I did the Export again, and the problem seem to be solved. But I'd like to export all tracks without having a limiter on master bus.

2- If a delay effect is present on some track (es: Calf vintage delay), if I bounce the tracks, at the beginning of the final audio file there's the "tail" of the delay sound. I understood that, if I bounce the songs after "waking" the delay effect, in the "audio system" (somewhere... i don't know where) there's a tail of the last sound that was processed by the delay effect. So, if I start Qtractor, listen to the song, and then bounce, I have this "tail" at the beginning of the bounce. If I start Qtractor and immediately bounce the song, without listening to anything, all is clean and normal.

Thank you!

rncbc's picture

re. 1- "exporting" audio is not quite the same as "bouncing": the first is a faster-than-realtime process that run *internally* to qtractor premises; the second is recording the normal playback output in real-time, having the output signal going through *externally* via jack into its own inputs; the actual signal processing path is different in either case, so some slight differences might occur between the two. Not likely as much different but "different" as in theory, for sure :)

re. 2-what you're experiencing is probably leftovers in the plugin own buffers when stopping playback (or export) abruptly at a point where there's still a significant data in the plugin buffers to be rendered out (the remaining "tail" as you say); it is a nuisance, i know, but rather difficult to tackle in general sense, at from the host side (qtractor); sorry about that.

re. 2-

manu_controvento's picture

Hi, ok, thank you, everything is clear. So, concerning point 1, the only way to have a real-time export is to connect a recorder (e.g. Audacity) to Qtractor's outputs. Otherwise, the method of a limiter (no hard limiting: just preventing from clipping) on master bus when exporting, is a good compromise, it seems working properly.

Is there a way to export MIDI in real-time (without the faster processing)? I'm running into an issue where the timing is off with the playback in the bounced audio.

For example:
MIDI playback goes: T-T-T-T T-T-T-T
Bounced MIDI goes: T-t-T-t T-t-T-t ... or sometimes T-t-t-T t-t-T-T

Thank you in advance

rncbc's picture

please read my first comment reply in this thread: you're probably asking to "export audio";

while "exporting MIDI" results in a merged standard MIDI file (SMF) and not an sampled audio one (PCM): is that what you're referring to? is the timing on the MIDI stream in that file all wrong?


My mistake! Yes, I was referring to Export Audio (as in bouncing a MIDI track to an audio track). :D MIDI playback sounds fine, but I'm noticing that the audio conversion is not keeping consistent timing. I tried resetting my QjackCtl settings, which helped some, but I'm still noticing some noticeable irregularities with the Exported Audio as it nears the end of the track; 100bpm is about 4mins long.

rncbc's picture

please detail or tell about your session a little more: which plugins on which tracks, whether any of those plugins are set to depend on the host timebase (eg. arpegiattors, echo/delays, etc.); whether there are any automation in place; anything else you may find special in your case that may help in analysing the situation.


Sure thing. Here are some details. Please let me know if you'd like to know anything else:
* 48 Hz, 24bit
* Hardware: Steinberg UR22, ASUS N55SF i7
* OS: Ubuntu 18.04, 4.15.0-50-lowlatency
* Two tracks: MIDI and bounced audio
* Chain: Carla Rack > Dimension Pro 64bit > Master Out (default)
* No FX

Of additional note:
* The full project has many more tracks, but I saved as a new project, removing all other tracks in order to try to identify the source issue - I could still hear some timing that was not quite right
* I previously worked on this at 96 Hz. There were LOTS and LOTS of xruns, but bouncing MIDI to exported audio (new audio track) did not produce any audible irregularities with timing
* As previously mentioned, I played around with QjackCtl settings, and it appears to have helped some; there was nothing scientific. For example, I changed the sample rate from 48000 to 41000 and then back to 48000, changed period/buffer from 2-3, and changed Frames/Period... and then finally resaved. I'm considering wiping out the profile and starting from new.

If you have any recommendations, I would gladly welcome them.

Many, many thank yous!

rncbc's picture

i gather that the instrument plugin at stake there is the so called "Dimension Pro 64bit", which I believe is a Windows VST2 (ie. running under wine via carla bridging), right?

just for the peace of mind, can you replace that, and maybe carla-rack altogether, for some native intrument plugin, preferrably a sane LV2 ?
and then 1) export the the audio and also 2) bounce/record the audio output (at Master Out) and check the audible differences between the two results?


Yes, you are correct. Dimension Pro is a VST2 running through WINE. I knew this was a risk from the start, but since I didn't have any issues at 96000 Hz, I didn't think there'd be issues at 48000 Hz. I will report back to see if that is indeed the issue. Thank you.

I just tried out AVLdrums on one of the tracks, and I'm not hearing a huge difference between the MIDI and exported track. So, I don't have enough to report on right now. It might be Carla to Wine, as you've suggested; I will upgrade that and continue to do comparisons. I also plan to clear out my QjackCtl settings to start fresh. I will write again with more details as I get them. I appreciate your time.

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