FFT Filter Bug with MultiChannel (Polyphonic) Clips

Report · Oct 10, 2017

I filed a bug report on this, but I figured I'd post it here, as well. The FFT Filter now nukes the last channel in any clip that has more than two channels in it. This is a real annoyance for me, as batch-applying "Kill the Mic Rumble" is usually my first step in a film sound edit.

Here are the steps to reproduce the bug:

In the Waveform Editor, open a clip with more than two channels.
Apply the FFT filter

Results:

As soon as the filter finishes processing, the highest numbered channel will become silenced. Waveform and spectral display will now be blank for that channel, and no sound will be audible from it.

Expected Results:

All channels should simply receive the application of the filter. None should end up silenced.

Workarounds I can think of are:

Split out to multiple mono files and apply the effect to each
In the Multitrack Editor, use the filter in the effects rack, so that it doesn't have to be applied.

Neither of these workarounds is a particularly good solution. The first one is time consuming, and negates the benefits of the new multichannel workflow. The second one adds significant processing overhead, over the course of a feature film sound edit (hundreds or even thousands of clips).

Anyone have any better ideas?

Report · Oct 10, 2017

I've just tried that here with an 8-channel noise file, and one of the presets from the FFT filter, and it doesn't happen at all on this system - it works perfectly...

Report · Oct 10, 2017

Interesting, Steve. On my end, it's happening every time.

On the one hand, as an altruistic human being, I'm glad to know that not everyone is suffering from this. But on the other hand, the inconsistency will likely will make the bug all that much harder to squash, which could be really bad for me.

Would you mind listing your system specs? I'm curious what might be the cause of the different behaviors, and that's as good a place to start as any. Thanks.

Report · Oct 10, 2017

I have just tried it here with a 5 ch surround file and I get the same result as ABBloch with the last channel silent after processing with the FFT filter. However adding a sixth channel and it worked OK. Maybe it is something to do with working with pairs of channels. Even numbers OK, odd numbers last channel goes silent.

Haven't tried it with any other odd/even number of channels since I don't have any others to hand

Report · Oct 10, 2017

I've tested your theory, Ryclark, and you're correct. The problem only happens when there's an odd number of channels. Clips with 2, 4, 6 and 8 channels work fine. In clips with 3, 5, or 7 channels, the last one gets silenced. I didn't bother testing beyond 8.

Time to update my bug report.

For now, unless someone has a better idea, I guess my workaround will be to include an extra channel when recoding anything that would otherwise be odd numbered. It won't help with pre-existing files, or files created by others, but at least it will work for my own stuff going forward.

Report · Oct 10, 2017

Seems reasonable. I ran out of time this morning, otherwise I would have tested this a bit further myself, but between you, you appear to have nailed it!

Report · Oct 10, 2017

I've submitted a new bug report, detailing our findings. Hopefully, it won't be too long before they can whip up a fix.