Pro Tools Mix Bus loses db?

[d_matt]

I have mix bus compression set up in the session I am working on.

I've noticed a few times when I'm doing A B's that a peak level on an audio track will be a couple db lower once it has arrived to the master fader. Now there are no plugins in the signal path and the send levels are at 0db. Is this a known bug or does Pro Tools perhaps lower the levels on busses to avoid distortion? What's up?

[Rail Jon Rogut]

Explain exactly what you have and how you're A-B'ng it.. the gain in PT has always been right in any tests I've ever performed.

Rail

[d_matt]

Thanks Rail,

The Kick track is peaking at -6db (using post fader metering). I don't have the output of the kick track assigned - I have it sending to a bus called 'Main Mix' (the send level is 0db). There are no plugins on the kick track or 'Main Mix'.

When I ctrl-click the peak indicator on the Main mix aux input, it reads -8db.

Where did that 2db go?

[Rail Jon Rogut]

Are you sending on a mono or stereo buss.. this sounds like a center panning law gain drop to me.

Rail

[d_matt]

It's a stereo bus. I don't understand, so, because it's a stereo bus the gain is reduced? Does it mean I need to have the send at +2?

[Rail Jon Rogut]

In Pro Tools the center panning law is a 2.5dB drop when you're panned to center.. you get unity when panned either hard left or right.. this is normal in console design.. although the correct value is 3dB.. this value varies by console manufacturer (SSL is -5dB at center). If you're feeding a signal via a stereo buss send and it's anywhere but hard left or right.. the cosine/inverse cosine panning law is applied to both channels. If you don't want to pan the signal, and you don't want to raise the gain.. create two mono sends each at unity.

Rail