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Topic: Downmixing 5.1 to quad (Read 4240 times) previous topic - next topic

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  • romor
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Downmixing 5.1 to quad
I read recent thread about mid/side separation, and thought to try this as simple downmixer:

Would someone add anything to this, or maybe some correction, for typical diagonal speaker placement?
  • Last Edit: 29 November, 2010, 01:09:44 AM by romor

  • romor
  • [*][*][*][*][*]
Downmixing 5.1 to quad
Reply #1
Now this doesn't look good
It's fine for movies, but for some music releases (DTS CDs if that matters) it gets ping-pong/helicopter effect and it generally doesn't sound good

I feel sorry for posting it without proper testing

[edit]
Talking to myself again
Actually it's not that bad, above happens on 2 CDs for which I'm not sure about their origin, so I will correct myself and say that it generally sounds fine also for music
Till next time
  • Last Edit: 29 November, 2010, 12:50:45 PM by romor

  • Rescator
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Downmixing 5.1 to quad
Reply #2
The way many implementations does it are either:

LFE discarded
Fc discarded
Ls to Ls unchanged (1.0)
Rs to Rs unchanged (1.0)
Fl to Fl unchanged (1.0)
Fr to Fr unchanged (1.0)

or they are:

LFE discarded
Ls to Ls unchanged (1.0)
Rs to Rs unchanged (1.0)
Fl volume reduction by half (0.5)
Fr volume reduction by half (0.5)
Fc volume reduction by half (0.5)
Mix Fc with Fl (0.5+0.5=1.0)
Mix Fc with Fr (0.5+0.5=1.0)

If you really must include LFE then you might try:

Ls to Ls unchanged (1.0)
Rs to Rs unchanged (1.0)
Fl volume reduction by half (0.5)
Fr volume reduction by half (0.5)
Fc volume reduction by 3/4 (0.75)
LFE volume reduction by a 1/4 (0.25) not sure if there are any common rules on this.
Mix Fc with LFE (0.5+0.5=1.0)
New Fc volume reduction by half (0.5)
Mix Fc with Fl (0.5+0.5=1.0)
Mix Fc with Fr (0.5+0.5=1.0)


It really depends on the mastering.
Sometimes the mastering has simply Fc as the same as Fl+Fr at halved volume.
While other times the mastering does not have the same content in Fc as Fl or Fr.

A lot of masters has Fl and Fr acting as fallback stereo with the other channels just enhancing the soundstage,
and as I said sometimes they may all be fully discreet.

LFE is more difficult and may cause more harm than good, it stands for Low Frequency Effect.
These days Fl and Fr are usually full frequency, and more recently Sl and Sr are as well (and possibly Fc too)
so if planning to mix in the LFE it's best to mix it with the center channel but at a very reduced level, then mix the new center with the left and right.

In all the years since LFE started being used it's mostly been for "rumble" stuff, music and FX bass are still in the Fl and Fr (and possibly Sl and Sr and Fc as well).
I can't recall hearing a "pro" mastering where the LFE actually has "normal" bass content that you would expect to hear in the other channels.

So listen through the source and make a decision, as you are essentially re-mastering the master in a way, so it would be silly to just blindly mix it.
For all you know you may only want to mix in the LFE at certain points but not at other points, etc.
Center is also used a lot for dialog so you may need to crank that up a bit (thus forcing you to turn left and right down a little in response).

Sorry I couldn't give you an easy answer, then again if sound was easy Hydrogen Audio would never have existed so...
  • Last Edit: 18 December, 2010, 06:54:17 PM by Rescator