[IDEA] Phase/Polarity adjust about audalign

[benfmiller]

Thank you for the references!

In what context do the phase/polarity errors occur?

The spectrogram-based recognizers (everything except for the correlation recognizer) are much too inaccuracurate time-wise to account for phase. They are accurate to about 0.04 seconds with the default settings.

I would think that the correlation recognizer would properly handle phase? Especially if you were to use the correlation recognizer during the fine_align step?

Could you send audio files and describe the code methods so I can reproduce the issue?

[MarcoRavich]

Well, as very well explained above "resources articles", phase/polarity issues occours when a live audio performance is multitracked from 2+ different source points.

To have a Check out this photo:

As you can easily understand, after the synching of all audio tracks (expecially with cameras' ones) it's is quite likely that phase cancellations could be generated.

Here's an interesting explaination video about phase/polarity:

Note that some commercial A/V synch software - like PluralEyes, for example - does automatically performs audio drift correction (a kind of phase/polarity fix ?) when needed.

Again, dunno if it falls within the scope of the project, but would be certainly very useful to have.

Last but not least, I hope that some of the mentioned phase correction softwares' authors can provide expertise on the subject for phase fixing techniques/details.

Thanks in advance.

[benfmiller]

Have you observed this problem with specific audio files or using specific recognizers?

Again, correlation should accurately account for phase. The other recognizers are way too inaccurate time-wise due to the spectrograms for phase issues to be an addressable concern.

I don't think addressing polarity in audalign would yield meaningful results and that it would be better addressed in a DAW afterward.

Are you suggesting that phase alignment be applied after every alignment?

[x42]

With multi-mic recordings, it is rather common to flip the polarity of some channels. A common example is snare drum top/bottom, mic'in. Phase cancellation (comb filtering) is rather obvious in that case. It other cases it be more subtle. e.g. when using a figure-8 mic.

One can aid detection of which polarities to invert by correlating channels. Harrison Mixbus for example has a built-in tool for this: https://youtu.be/f_f8G5tnkfk?t=272

Phase rotation or sub-sample alignment is of no real concern for alignment.

I don't know audalign, so I cannot judge if such a feature would be better addressed there or in a DAW.
However IIRC Sonic Visualiser takes phase into account for https://www.sonicvisualiser.org/sonic-lineup/index.html but I'm pretty sure that it does not match polarities either.

[MarcoRavich]

I have recorded dozens of live music shows, but I have been able to listen phase issues with my ears in huge stage or classical music performances.

Of course, phase and/or polarity correction/optimization must be performed AFTER alignment - that's why I was wondering if it could fit within the project's scope - but certainly they should be user-selectable additional options and not done by default.

@x42 Thanks for your interesting contributions which allowed me to discover Music Alignment Tool CHest !

[benfmiller]

Thanks again for the resources! I'll definitely look into a post-processing phase alignment function

[MarcoRavich]

Bump.

Just discovered this deep learning-based project for the "issue": @karisigurd4's StereoPhaseNet !