Last week, Chris Huff had a great post over at Behind the Mixer that explained the differences between pre- and post-fader aux mixes. He said, quite correctly, that you generally want monitor mixes to be pre-fader, and FX sends to be post-fader. I totally agree with that, and run my auxes that way almost all the time.
This post is going to be about when it makes sense to break those rules. Keep in mind that this is a compliment to, not a criticism of Chris's post. But first let's review. You generally want monitor mixes to be pre-fader because you don't want changes made to the house mix affecting the monitor mix; most of the time. Every once in a while, however, that's exactly what you want. Let's look at some examples.
Stem Mix Research
Let's say you find yourself mixing some submixes or stems for a personal monitor mix (aka Avioms or M-48's). With Aviom's especially, it's not hard to use up all 16 channels and still need more. So, you may have to submix certain things, perhaps your playback channels (iTunes, video, etc.) and speaking mics. If you mix all those sources down to a single aux, you can save a valuable channel count, and still give the musicians the information they need.
However, let's say you run all those pre-fader; what's going to happen? Well, they're going to hear your pastor singing during the worship set, if you forget to stop iTunes at the beginning after you fade it down in the house, they'll get that too, and you'll have some great ambience happening with the open announcement mics. Not optimal.
Instead, let's set those to post-fader. In post-fader mode, the only time any of those channels show up in the IEMs is when they're actually being used. So the band will hear iTunes fading out, and they'll know it's time to start playing. They won't hear the pastor until he actually takes to the platform to speak, and the announcement mics will be silent until announcements. Pretty cool.
Sometimes you might get a request to put the pastor's mic in the wedges so the singers can hear the pastor talking between songs. In this case, if I can send him post-fade I will. The reasons are again obvious; when I fade down his mic at the end of his talking time, I want him to leave the wedges.
We do this at Coast; we have two aux mixes for these stems—a playback foldback for iTunes & video and s speaking mics foldback for, well, speaking mics. Mixing all these sources post-fader also has the effect of keeping the level relatively consistent. Which leads me to another use case.
This one might be a bit specific, but it totally saved our bacon at Christmas time. During our huge theatrical presentation, Gunch!, we had something like 16 channels of actor wireless. Because so many of the musical cues were keyed to actors lines (and many of the actors sang as well), the band really did need to hear the actors. However, trying to get 16 actors dialed in to a pre-fade mix would have taken a long, long time. I know, because I tried to do it. After about 15 minutes of holding up 120+ people, we needed a better way (we were less than 1/3 the way through).
We made the decision to switch to post-fade for the actors. The idea is simple; at FOH, I was working to keep the level of the actors consistent in the house by riding faders. So, if I was doing that in the house, setting the aux up to track the faders (by going post-fade) meant the level would be consistent in the foldback as well. It took just a few minutes to establish the send level for all the actors mics, but once we had that, I kept it even in the house and the musicians were happy.
Since we had actors ranging from little kids to semi-professional actors with an MBA in theater, running the mix this way was a huge win. We also had actors whose dynamic range went from a whisper to a shout; again, by tracking the aux mix level with the house fader, everyone was happy.
These are a few ways I've used post-fader sends; how do you use them?