Realtime vs. Non-realtime Export Issue


Should I expect an exported MP3 to be the same irrespective of whether I choose to export it with the “Realtime Export” option enabled or disabled?

The reason I ask is that I get dramatically different results with the two options. And by dramatically different I mean that I can easily tell the two apart by ear; the non-realtime option being inferior in that the timing of instruments is way off.

Is this another “known issue” waiting to be resolved, or a new one for 10.5?


You should expect the very same results. Could you attach an audio samples (MP§ exports) where do we hear the difference, please?

Hi Martin,

I hear differences throughout the entire ~2:30 length of the song. The most noticeable differences are in sounds with sharp transients.

After finishing the song I exported it without realtime export enabled (because exporting with this option sometimes fails given the large number of plugins used in the project). But when I listened to the MP3 file, it sounded different. Initially I thought the difference was due to poor mixing. So I went back into Cubase, make some more tweaks, re-exported, and listened again. After a few trials of this I realized that it was not me – it was Cubase!

So to see what was happening between the two options, I created some plots that comapre the two exports.

Note, they were made one right after the other – i.e., nothing changed between the two exports. But just to make sure, I repeated the export process three times (as well as the order in which I exported the MP3 files with/without the realtime export option).

The first figure plots MP3-1 (non-realtime export) against MP3-2 (realtime export) for both the left (blue) and right (red) channels. If the two files were identical, you’d see a 45-deg diagonal line. And this is, in fact, what you see when you plot MP3-1 versus itself (that’s the black diagonal line). However, when you plot MP3-1 vs. MP3-2, you get a cloud of points that shows they’re quite different.

To visualize the difference in the waveforms themselves, compare the two plots below (which show the first 250-750 ms of each waveform on the same X/Y scales):

And here’s a screenshot of the project:

As soon as you have modulating stuff or VSTis in your project two different exports aren’t likely to null.

Please repeat the test with something simple like a static event without plugins and see/hear what you get and how real time/non real time compare.

My guess would be a VST or VSTi misbehaving.

Non linearities of plugin. They simply cant sound the same everytime, such as some tape fx

This has been tested before and are mostly Plugins that react different. The question is what is the best method to getting what you hear from cubase while mixing it in realtime, must be the realtime export. That does not mean plugins react different to buffers send and comming out, there is a possibillity that one or more plugins react diffently. Next some plugins like compressors or any latency plugins, like to run at an higher buffersizes, because they Scan the audio to compress it or do something with the audio, that means find the plugin with the highest latency and set buffer even higher then that and try an export. It should then even sound different, because the plugins react differently on buffersize or lantecy time they get.

As fas as i know Cubase does an excellent export on Audio tracks.
So there should not be any problems when you release all the plugins…

Lots of good suggestions – thanks!

Just to be clear, I fully realize that anytime you use certain types of plugins such as modulation, compression, distortion, the output will not be the same each time you run the project for a variety of reasons such as 1) the input-output transfer function is somewhat stochastic by design (particularly true for some modulation plugins), and 2) the output of some plugins (notable compressors and saturators) are input level-dependent.

However my specific problem is that the notes from a few of the VIs are playing noticeably and consistently late relative to the drums. There are no issues with pitch, timbre or modulation. The probelm is exclusively timing. It’s very acute for one plugin in particular: Waves Flow Motion (patch = SQ Seqs).

I took marQs’ advice (below) and removed all tracks except for the one with Flow Motion on it. I also disable (not just bypassed) all plugins. I then exported the measures where the timing issue is most pronounced with realtime export on/off. The result: the timing issue is gone.

However, I have now exported the full mix six times with realtime on/off.

  • Each of the six MP3 files resulting from a realtime export sound fine (just like in Cubase).
  • In contrast, all six MP3s generated with realtime disabled have the timing issue I described above.

I don’t know how to explain this. If anything I’d expect the exact opposite to happen: exporting with the realtime option should have timing issues because the computer is working under a greater resource burden.

Bottom line, I don’t expect anything further at this point since I have a workaround: export using the realtime option.

Thanks again to all who replied. Cheers…