Sanderxpander
Any plugs active on the ProChannel on the master bus? Or some other important submix bus...

Only the ProChannel compressor on one of the submix buses.  Disabling it doesn't make a big difference. 

What pan law are you using? Were you checking the mix in mono and forgot to switch the interleave back? Just a thought.

EUREKA!
It turned out that the ProChannel compressor was active on the Master bus. Turning it off brought the level back to normal. PHEW!
 
Use of this ProChannel module on this bus was not intentional and I don't know how it happened, as I didn't even have ProChannel visible on that bus in Console View. Nor did I intend to use any of the ProChannel modules on the Master bus, although I did use some of them elsewhere.
 
Anyway, thanks for all the suggestions (some of which were certainly on the right track).

Kev could you have possibly engaged the compressor *thinking* you were working on another strip?

Grem
Kev could you have possibly engaged the compressor *thinking* you were working on another strip?

That's probably what happened.
 
EDIT:
Or maybe not (see next post).

I've just discovered that the ProChannel Compressor was actually active on every single bus. This wasn't immediately evident, as the on/off button is off the top of the screen and only becomes visible if I minimise one of the other modules. There is no way that I could have set all of these accidentally.
 

Kev999
There is no way that I could have set all of these accidentally.
 

Actually, there is - it sounds like you invoked the quick group function accidentally. I use it all the time to make wholesale changes (e.g., turn all Console Emulations on and off, or adjust all their controls simultaneously). But there have been a couple times when an errant keystroke did so unintentionally.
 
Which reminds me of my tip of the day...never let a cat jump up on a QWERTY keyboard while a session is open. Just sayin.'

Anderton

Kev999
There is no way that I could have set all of these accidentally.

Actually, there is - it sounds like you invoked the quick group function accidentally. I use it all the time to make wholesale changes (e.g., turn all Console Emulations on and off, or adjust all their controls simultaneously). But there have been a couple times when an errant keystroke did so unintentionally.

That seems very plausible. Quick Groups is a feature I've never even considered using. I guess that it's advisable to know something about all the features you never use, just to avoid being baffled whenever you unwittingly activate something.

I posted about something similar just a week or so ago. QuadEQ became "active" on every single track, and the low frequency gain was turned all the way up on every track. Took me awhile to undo it.
 
I never use Quick Groups either, guess I need to read more about it.
 
Regards,
Dan
 

Quick Groups are great, but you need to use this power only for good