Downmixing...

[ramicio]

I manually downmix DTS-HD Master with Goldwave for my own encodes. I mix everything at the same level and then reduce volume later. I noticed with downmix profiles like DPL2 that they reduce the center channel. Why? The files I make sound fine to me. I can't find any info on non-DPL2 mixing, and I was wondering how the LFE and surrounds are mixed in (dB). It seems they mix the Center in -3dB. If it is a master file, I would think that nothing was done to the tracks and the actually DAC would do any level changing as needed. Is that a totally off the wall way of thinking of this?

[mp3dom]

The LFE most of the times is discarded when downmixed to 2.0. You can anyway decide to include it with -mixlfe flag (eac3to). In general, stereo systems are unable to cover bass frequencies very well so in general LFE is discarded.
Regarding the -3dB, the Center channel is equally splitted onto left/right channel during downmix. If you add a sound with the same sound, the volume increase 3dB. Adding left+right will return the center channel at its original volume.

[tebasuna51]

Stereo mix:

FL' = FL + 0.7071 x FC + BL
FR' = FR + 0.7071 x FC + BR

The acustic power contribution of center channel in 5.1 is proportional to FC ^ 2
Now there are two components (in FL and FR):

( 0.7071 x FC ) ^ 2 + ( 0.7071 x FC ) ^ 2 = (0.5 + 0.5) x FC ^ 2 = FC ^ 2

Then we have the same acustic power contribution than before in 5.1.

You can use the same coefficient for LFE. (Dolby don't recommend use the LFE channel in downmix)

[ramicio]

I won't use eac3to to downmix because it does so with a DLP2 profile. I don't need an kind of phase shift on the rears for a Master Audio file. That explanation half makes sense about the -3 dB, for pro-logic, but not for something that was discrete to begin with.

That's all for Dolby, but DTS is a different story, right? This isn't for a receiver either. I use head phones. Is there low frequency in the audio anyway? By that I mean as low as what's in the LFE.

[tebasuna51]

I don't speak about dpl downmix, the mix I put is regular stereo downmix you claim: "I can't find any info on non-DPL2 mixing".

You can add the LFE channel:
FL' = FL + 0.7071 x FC + 0.7071 x LFE + BL
FR' = FR + 0.7071 x FC + 0.7071 x LFE + BR

Sometimes can produce artifacts, ... or not.

[ramicio]

I just use -down2 when i reencode movies for my iPhone, because I am only encoding to AAC. I mixed a stereo file with -3dB on the center and LFE and it kinda sounds better.