Audio distortion #163

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iamjaydear opened this Issue Jan 7, 2017 · 3 comments

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@iamjaydear
iamjaydear commented Jan 7, 2017 edited

For about a month I have been experiencing a strange audio distortion which I think sounds a bit like a damaged speaker cone or bad noise gating, so I thought I had a problem in my soundbar. I've been putting up with it, but now it's really bugging me and I'm trying to find the problem. I've discovered that the soundbar is not faulty, it's my mp4 files!

As near as I can determine, around early December there must have been an update to VC / HB which introduced the distortion. I've seen other reports on the web variously describing it as underwater sound, low level crackling, rumbling distortion, etc. Rumbling is a good clue - the distortion seems to be generated by low frequency content which would not be audible on little loudspeakers such as those used in flat panel TVs.

Are you aware of this problem? Some of the "cures" I've seen on the web are more like snake oil (change the sample rate, change the codec, use auto instead of specific settings, etc.). My processing settings have not changed for a very long time, and the source files seem OK through the same playback chain. Before I changed to VC I used WinFF and it was all good until an update to ffmpeg (which I believe HB also uses) borked the video codec I was using. I hope that they have not killed x.264 like they killed XviD.

Any insight and support you can offer would be very, very welcome. I do not have the spare time to try and research this problem properly or to battle the HB devs. I don't even know how to report an ffmpeg problem - it's as if those devs are on Mars. I'm happy to prepare some samples for you if you are interested to help cure this. Other VC & HB users will eventually realise there is a not so subtle problem in the audio.

@RandomEngy
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Thanks for the report, though I wouldn't be the one able to fix this. The fix would come through an update in the HandBrake core, so you're better off reporting to them.

@iamjaydear

I'm disappointed of course but understand that you have no influence over the internals of HB and ffmpeg despite having written such a popular front end. I will try to dig down and get some evidence to present. I've observed that the HB devs are quick to dismiss if you don't give them solid proof. I don't write code, so that avenue is closed to me.

@iamjaydear

Issue #166 is holding me back at present. Tests I've done so far point to intermodulation distortion as the culprit. Is it reasonable to assume that the code in HB (and VC of course) is unlikely to be able to cause this do you think? If so, then it would have to be a problem in FFmpeg, which in my mind is a flippin' disaster. In my listening tests yesterday I found that: a/ The distortion is hard to hear on the pathetic speakers in flat panel TV's, b/ Is not so apparent on a high-end HiFi system, and c/ Is really obvious and unpleasant on my JBL sound bar - probably because 1. The speakers are small and 2. JBL do some fancy filtering, dynamics control and phase manipulation to get a wide sound field (as would any sound bar manufacturer). Older mp4's from VC with similar content sound OK on all the above systems, and recent ones have the distortion. Next, if possible, I want to try comparing mp4s from VC 1.5.33 and 2.44, from an mpeg2 source file and processed on the one PC, in Audacity.

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