@Luke Smyth
(Thanks for joining the stream today!)
There are a few things to unpick here.
Mix External In - These are for an external input to a mix (rather than an input for an external mix). They add unprocessed signal from an input socket or sockets (analogue or digital), without any processing or routing options, so no EQ, level or mute for example.
If you’re just wanting to take a signal from pro tools and convert it to analogue (to convert back to digital in the ATEM!) then Tie Lines are probably your best bet.
Tie Lines route any input socket to any output socket, so you could send your master mix from Pro Tools on USB inputs 1&2 straight to jack outputs A&B for example, and then use a common 2x 1/4" jack to 1x 3.5mm stereo jack to connect to the ATEM.
(Make sure your ATEM is set to line input)
As far as the differences in sound and level, no, you generally wouldn’t see a drop of level, or thinning of sound because you used USB.
If anything, it’d be the contrary - USB is carrying the signal digitally, so generally it will either work or not work (or maybe if only some of the data came through, perhaps cut in an out), whereas analogue cables have a lot more ‘in between’ states of working, which could affect frequency/level/distortion.
I’d definitely recommend checking the signal at every point along the chain, so you can find where it’s going wrong, but with the information you’ve given, It might be that you’ve got the original signals (inputs in your broadcast SQ) going to the LR mix, then, using the Mix External Input, you’re adding the Pro-Tools-processed signals back in alongside these???
If this is the case, then due to the latency introduced by the loop out and back from the computer, you’d be adding similar signals which are not time aligned/coherent. This can cause phase cancellation and comb filtering. It would affect particular frequencies depending on the latency time as well as level, kind of like you describe.
(if you’re interested in really fun graphs… https://youtu.be/LjPXMSlW8aM?t=905)
The easy answer to that would be to either use the SQ audio as is, or send everything to Pro Tools and use only the Pro Tools output, but not both alongside each other.
Slightly more involved would be to use inserts on the channels (if using less than 32) and have each channel in Pro Tools used as an insert on each SQ channel. Then ensure Pro Tools is phase aligned and that all SQ channels have their inserts on, so latencies are matched.
If everything you’re monitoring by PAFL’ing the mix output on the SQ or listening to the input on ATEM sounds fine though, it would suggest something strange downstream from the SQ.
Hope this helps.
Cheers,
Keith.
