So, I’ve been thinking about stem mixing recently.  In case you’re not familiar with the term here is a definition from Wikipedia:

Stem-mixing is a method of mixing audio material based on creating groups of audio tracks and processing them separately prior to combining them into a final master mix.

So essentially this has everything to do with how you route signal through the sound board to the outputs.  Currently I don’t use stem mixes much, for several reasons.

1) The console I use (a Crest V12) has twelve VCA groups which I use to control the signals of multiple inputs together or as a ”group” (such as drums or strings). So I can control groups of signals but these groups don’t actually combine the signal and route it to a bus.  Instead, they merely control the output of each signal (p.s., this is the key difference between a group and a VCA-group, for more of VCA Groups click here).  Therefore the use of VCA’s can basically eliminate the use of traditional groups (or buses,or stems). And without stems, you won’t be doing any stem mixing.

2) Also the way our system is designed the main buses (L,C,R) feed the system processors that eventually get to the amps and then to the speakers and finally to the congregation.  For a system that employees stem mixing, the mains are normally run off of a Matrix Send (because this is often where the stems are combined).  So using groups (or stems) on the console and system I do would only serve to complicate the signal path and not have many practical advantages for the main mix (it does still have advantages for the distribution feeds).

3) The combination of #1 and #2 essentially mean a “cleaner” signal path.  That is why VCA groups have become so popular (that and making post-fader aux-sends way easier when using large number of inputs).  Because there are less summing-amps used the signal path remains as un-cluttered as possible when you simply go into the pre-amp, through the channel fader, and out the main bus (that’s very over-simplified, but it gets my point across). Some even might argue that slight phasing problems can dirty up your final signal when using buses (a problem that can be much worse on digital consoles because of processing time).

However, stem mixing has some great advantages too:

1) Groups can be processed together.  Because the group is actually combining signal, that group of signals can now be sent somewhere and processed.  So you can compress the entire drum set.  Although that isn’t recommendable, except maybe as an effect to add to the uncompressed version–I believe that’s referred to as the New York trick in recording.  Or all the choir microphones can be sent to a 31-band EQ to notch out the trouble frequencies causing feedback. This can be helpful if you are doing a more theatrical presentation using a few similar lav mics too.

2) Level disparities can be accounted for in distributed/aux mixes. Often in professional systems with lots of headroom for concert-level music, the signal on speaking voices (pastors, announcements) are relatively very soft.  This can cause problems for distributed feeds for the Internet or cry rooms or video recording if these are originating from the main mix only.  However, using stem mixing, a stem mix of the speaking voices can be sent at one level to the bus feeding the main house system, while feeding a stronger amount of that ’speaking voices’ stem to the distributed audio bus.  This can be used much more effectively (and much better sounding) than a simple compressor across these outputs.

3) ‘Mix-minus’ mixes can be achieved with greater ease.  A mix-minus stem is essentially the entire mix minus one particular element (or stem). Although a mix-minus system is a more technical and needed way to mix for many broadcast applications, it can also have many advantages in the sound reinforcement world.  For example, if a pastor has to lead worship but can’t sing very well, the congregation might cover up his voice in the main sanctuary, but not in the nursery.  So if we are using stem mixes, the stem that the pastor is on can be removed from the bus going to the nursery for the just the songs, essentially creating a kind of mix-minus feed.

4) The same groups or stems used in the stem mix can be convenient for sending to monitor mixes, either traditional or especially for all the new personal monitors system that might have limited channels.  Sending stems instead of channels to the personal monitors can actually be key to simplifying the use of these personal monitors for band members.

Well, that’s a small run-down on Stem Mixing.  I hope that is helpful.