Dolby PL II surround center channel issue

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Lostless
Posts: 53
Joined: Thu May 24, 2007 7:55 pm

Dolby PL II surround center channel issue

Post by Lostless » Sun Mar 08, 2015 3:12 am

Ive noticed in the recent version of handbrake, because my older encodes do not have this issue, that when converting a 5.1 source to DPLII that surround "center" gets moved to the right channel when there is a main center channel sound playing. Its like the matrix surround is not encoding properly and when playing back on a stereo system/headphones, vocals/anything in the center of the in the background music/sound effects gets moved to the right channel when people are talking. Stuff that would normally be in the left and right stay in the left and right. Playing the original MKV in VLC keeps all the background sound effects and music vocals in place.

http://pastebin.com/Mm4BJ7wm

Thats on of the encodes where i noticed the issue. Where it was really noticeable is in the ending where a song comes up and the vocals of the background music come up in the center. When the chorus comes up, the movie has people laughing from the main center channel, and the music vocals/some instruments suddenly get shifted the right channel. Also during the entire movie, the background music and ambiance was focused usually towards the right, but not that noticeable, because it only happens when the main center channel is being used.

For now i will just encode with stereo as it does not exhibit this issue.

musicvid
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Re: Dolby PL II surround center channel issue

Post by musicvid » Sun Mar 08, 2015 3:44 am

I've noticed this in other apps when the original Dolby Digital 5.1 was noncompliant -- iow the 90 deg. phase shift to conform the mixdown for PLII playback didn't get applied and as a result the balance got shifted to the right.
I have absolutely no idea if this has any bearing on your issue, perhaps indirectly at best.

Lostless
Posts: 53
Joined: Thu May 24, 2007 7:55 pm

Re: Dolby PL II surround center channel issue

Post by Lostless » Sun Mar 08, 2015 4:30 am

I think the issue you found is indirectly realted. Ran the original MKV with the 5.1 DTS (also had the problem with files that used Dolby digital as well) through MplayerX, and its mix down to stereo exhibited the exact same issue with the center surround shifted to the right with the main center playing. VLC doesn't do that. I think (may be wrong) MplayerX uses similar or the same open source libraries to decode video/audio that handbrake uses. VLC is on its own and uses its own libraries (i think). So it may be an issue that exists beyond handbrakes control and is a problem with the open source decoders that handbrake is built on.

Did a new test and the Dolby Surround down mix has the issue as well. Did another in stereo and no issue, but it does feel I lose some surround feel to the audio. No big loss as I mainly use 2.0 speakers most my time.

musicvid
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Re: Dolby PL II surround center channel issue

Post by musicvid » Tue Mar 10, 2015 2:02 pm

The libraries are essentially the same.
A guess is that your DTS 5.1 doesn't use the phase shift flag, as would a Dolby 5.1 decoder. Run the native 5.1 or stereo. ProLogic is generally horrible at best.

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Rodeo
HandBrake Team
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Re: Dolby PL II surround center channel issue

Post by Rodeo » Tue Mar 10, 2015 5:09 pm

musicvid wrote:The libraries are essentially the same.
Not really. We use libavcodec and libavresample for pretty much everything now, whereas VLC still uses liba52 and maybe even libdca, which have their own built-in downmix code…

As for this issue, I believe it mostly happens when there is a strong correlation between the left and right surround channels. We decided to not revert to how liba52 and libdca do their downmixes because while it happens to alleviate this issue, it's technically incorrect.

Lostless
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Joined: Thu May 24, 2007 7:55 pm

Re: Dolby PL II surround center channel issue

Post by Lostless » Wed Mar 11, 2015 12:25 am

As for this issue, I believe it mostly happens when there is a strong correlation between the left and right surround channels. We decided to not revert to how liba52 and libdca do their downmixes because while it happens to alleviate this issue, it's technically incorrect.
What is more correct? My Tv does not down mix 5.1 to 2.0 the that handbrake is with its pro logic. It down mixes the way that the "stereo" output does on handbrake. While it might be technically correct, its not correct in its intentional output. Center should not be shifted right.
Ill just use stereo from now on, because I don't know if i'm going to get the odd output or not on my rips.

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