Downmixer Plugin Presets Explanation

[Nathan W.]

Why is the System 5 default -6dB for the LS and RS but the Omni is -3dB for the LS and RS? I can't find any documentation explaining this.

[MatzeHD]

What do you mean, downmixing from 5.1 audio to stereo?
With which plugin??
Dolby recommend in the DD Encoder -3dB or -6 db for downmixing to L+S

[The Cargo Cult]

Part of the reason the sys5 uses -6 is that theatrical rooms are lined up with -3db surrounds.
So the re-recording mixer will have set levels 3dB too hot for the front channels.
the other -3dB accounts for pan-law for signals placed halfway and also the perceptual difference between speaker behind and speaker in front.
I think...

I'd love to know the downmix laws for the new PT12 output section.
Anyone...?