Ticket #29 (closed defect: fixed)

Opened 2 years ago

Last modified 1 year ago

Dolby Pro Logic II output (surround in a stereo signal)

Reported by: anonymous Assigned to: gbooker
Priority: normal Milestone: 1.7.5
Component: a52codec Version: 1.7.2
Severity: normal Keywords:
Cc:

Description

What about downmixing the 5.1 signal to stereo Dolby Surround Pro Logic II (or IIx)? That would recreate part of the 5.1 experience, on compatible receivers, even if Apple does not bother letting Quicktime passthrough 5.1 sound to SPDIF in. I think WIndows' AC3filter can do this.

Some threads on the subject that google popped up without much effort:

* Doom9.org Forums: 5.1 AC3 > Dolby Pro Logic II AAC?

* AC3Filter.net: Documentation on enabling DPLII output

* Doby.com: Dolby Prologic II FAQ

* (PDF!) Dolby.com: Mixing Information for Dolby Pro Logic II

Change History

04/07/07 15:48:43 changed by gbooker

  • status changed from new to assigned.
  • version set to 1.7.2.
  • milestone set to 1.7.5.

The liba52 library already supports DLPI output, and it is actually used by default. DLPII is not within the library, but shouldn't be too difficult to add. I found a patch to the liba52 on the handbrake forums which adds support (but only for 3F2R configuration). This just needs to be expanded to support 2F2R and 1F2R and it should be good to go (no point with 1R because DLPI supports mono surround just fine). Anyway, as a note to myself: http://handbrake.m0k.org/trac/browser/trunk/contrib/patch-a52dec.patch

Perhaps in the next milestone?

04/07/07 17:33:20 changed by gbooker

  • status changed from assigned to closed.
  • resolution set to fixed.

(In [43]) Pro Logic II support. Closes #29

04/10/07 11:57:18 changed by anonymous

I'm sorry to be an ass, and just to know…

There is apparently no consensus on the better way to transcode from DD5.1 to DPLII. http://forum.doom9.org/showthread.php?t=112122 is the last source I could find were extensive experiments were openly carried out.

How does your fix relate to the discussion linked. Does it address their concerns anyway?

04/10/07 23:28:37 changed by gbooker

Its doing the:
Lt = FL{0°} + 0.7071 C{0°} + 0.866 SL{0°} + 0.5 SR{180°}
Rt = FR{0°} + 0.7071 C{0°} + 0.5 SL{180°} + 0.866 SR{0°}

The reason is that a hilbert transform (90° phase shift) is a pain in the a** and I really don't feel like making the FIR/IIR filter to do it.

LFE is not mixed in because from what I read on the Dolby site, it appears that it should not be used. Also take note of http://en.wikipedia.org/wiki/Dolby_Pro_Logic#Dolby_Encoding_Matrices