Mixing for live streaming doesn't have to be difficult, but there are a few key things to keep in perspective, in order to get great results. I'm going to point out the big ones here, like speech vs. music levels and the use of audience mics, and then talk briefly about the typical ways people manage their broadcast mixes. And notice that I'm referring to this as broadcasting, as that's exactly what a web stream is.
In fact, the way you mix for a web stream is no different than mixing for television. Either way, there's someone watching or listening in their home or at work. They want to hear the same qualities in the mix regardless of how it gets to them.
Remember that remote viewers/listeners will have a significantly different experience than those in the room during worship.
One of the biggest challenges is that the blend we want to hear live in a venue is often quite different than what we'd want to hear somewhere else. For example, in a small room, you may not have a lot of drums in your mix, because they might already be plenty loud acoustically. However, a broadcast listener will certainly want to hear them. In addition, you might have the vocals "on top" of the mix quite a bit live, because the congregation likes that, but that may not sound good on a broadcast. You also may like to have a really dynamic mix live, because it's exciting and sounds more "open" than one which is heavily compressed. However, the better broadcast mixes tend to have a more restricted dynamic range, to give the listener a more consistent experience.
Another common issue is that we tend to enjoy quite different levels for music and speech in a live setting, with there often being as much as a 20 dB difference in what feels right live. For example, let's say you mix your music at an average level of 95 dBA.
That might be nice and energetic, and gets everyone on their feet worshiping, but speech that loud would probably send people running for the exits.
On a broadcast, though, those segments need to be roughly at the same level, or viewers will constantly have to adjust their volume to chase the drastically changing mix levels.
Depending on your room, you may or may not add a lot of effects like reverb and delay to your FOH mix. You might add a lot of reverb, because it could be hard to notice in your room, and so it takes a lot before you get the desired effect. Or you might not add any, because the room is already reverberant, and you don't feel like you need any.
The broadcast audience, though, needs some effects in the mix so it feels right, but it likely needs to be a different amount than what you're doing live. Too much and it sounds cheesy; too little and it sounds too dry and "in your face." It's hard to judge what will sound good for the broadcast while you're trying to mix FOH.
Here's a big one. When you're in the room, you can easily hear the sounds of the congregation singing, clapping, and laughing at the pastor's "jokes." But because the instruments and vocal mics are all capturing fairly isolated signals, you need additional microphones just for broadcast to capture the congregation's energy. These "audience" mics are typically small-diaphragm condenser mics hung throughout the room (and aimed to reject sound from the loudspeakers). It takes some experimentation with location and height, but once you get it right, the results can sound great.
Some people put a pair of microphones (often, but not necessarily, "shotgun" mics) in front of the platform facing toward the front rows, and those can double as ambient mics for musicians wearing in-ear monitors. However, when used as the only audience mics for broadcast, those will pick up a small group of people, and may not get results as good as hanging mics.
Now that we've identified some of the major challenges, let's talk about how to manage them.
Ideally, you want a separate mixing console and audio engineer to handle the broadcast mix, for all of the reasons above. It's particularly helpful if they are somewhat remote (at least outside the worship space) so that they can listen accurately and make good mix decisions that will translate to the broadcast. This console should receive a split of all of the microphones, plus the audience mics. This will theoretically allow for an excellent broadcast mix, and it's how major productions do it.
However, this is also the most expensive route.
The next best thing would be to have a separate small mixer, which may or may not need to be operated by an engineer all of the time. You'll send a stereo mix of the band and vocals as the "music stem" to this mixer (by utilizing either audio subgroups or, better yet, a stereo auxiliary send on your FOH console). You'd also send all speech mics as an additional stem via a subgroup or auxiliary out, so that the levels of those mics can be significantly boosted for broadcast at the broadcast mixer (remember that this will then allow music and speech segments to match in level for broadcast, because we usually don't mix them that way live).
These music and speech stems should be fed entirely post-fader to broadcast, so that any fader moves at FOH are reflected in broadcast, which is usually a good thing with this type of setup. The final set of inputs for the broadcast console would be the audience mics, which might simply be left on the entire time, or, if an engineer can attend to the mix, he or she can ride the audience mics up or down to suit the moment.
The least ideal, but often most practical way to accomplish a decent broadcast mix, is to do it entirely from FOH. In this case, you'll typically use a stereo aux, and put all of the music and vocals post-fader with an initial aux send level of -20 (I recommend this default level, because it gives you plenty of room for the speech levels to be hotter than music, and for any variations you want to add to the music blend for broadcast). Then, via experimentation, determine how much higher to send the speech mics to this aux bus so that the program level is consistent from music to speech.
Finally, add the audience mics to this aux bus, but most importantly, do not allow those mics to get to the PA! For this to work, it's best to both disengage those channels from the main mix bus, and send them to the aux bus pre-fader, with the faders down.
You may also choose to add an overall compressor and/or peak limiter to the broadcast mix to help keep levels more consistent and to get an overall hotter broadcast level (if needed). You may also want to invest in a hardware- or software-based broadcast level meter, to help you keep an eye on broadcast-standard mix levels and help you learn to mix for broadcast more consistently. While outside of the scope of this article, search for terms like ATSC A/85, BS.1770, LKFS, and LUFS to learn more.
The key principle underscoring all of this is to remember that remote viewers/listeners will have a significantly different experience than those in the room during worship. We need to be mindful of what doesn't translate well and compensate for it in the broadcast mix.
If you address everything in this article, you'll be well on your way to a very happy audience. Happy broadcasting!