EngineFilterIIR assertion failures (can be triggered by syncing)

[x]

Randomly while mixing, pressing sync causes Mixxx to crash with this error:

Fatal [Engine]: ASSERT: "yv1[8]<100000 || yv1[8]>-100000" in file src/engine/enginefilteriir.cpp, line 59
Aborted (core dumped)

This happened twice in 10 minutes during my last session, but sometimes doesn't affect me at all

[x (broma0-deactivatedaccount)]

Seems as though it only happens when pressing the sync button.

[RJ Skerry-Ryan (rryan)]

This isn't really a crash, it's an assertion failure. We shouldn't assert on this condition so I removed it.

Also, the condition of this assert is pretty funny: yv1[8]<100000 || yv1[8]>-100000 will always be true for real numbers (including +/- infinity). The only double value this fails for is NaN which is not comparable to any number, even itself.

What this means is that one of the IIR filter coefficients has become NaN. I wish I knew more about why this happens. I've converted the assert to a stats counter and I try to handle the failure gracefully by zeroing out the NaN coefficient of the filter. If the earlier coefficients of the filter are NaN then this won't help at all because the NaN will just keep propagating.

Matt -- could you test version >=r3649? I'm very curious what zeroing the coefficients does when you trigger the bug. Worst case it will totally kill audio output for the deck (but it won't crash). If that does occur then we'll need to zero all the coefficients to fix it.

[Swiftb0y (swiftb0y)]

Mixxx now uses GitHub for bug tracking. This bug has been migrated to:
https://github.com/mixxxdj/mixxx/issues/6798