Stem mixing or ‘sub mixing’ is a useful tool for the producer or mixing engineer. Essentially it allows the mixer to consolodate tracks into single ‘stem’ groupd making it easier and more efficient to mix sessions with large numbers of tracks.
To set up a session using stem mixing you should first decide on how to group the tracks. For example drums would consist of kick, snare, toms and overheads. In the mix window route these individaul tracks to a new auxiliary track by selecting the output from the I/O and chosing a new stereo bus. These tracks can now be controlled from the new single aux track with respect to volume, panning and any extra plug-ins. By doing this with similar groups sucj as guitars and vocals the session can be controlled by a handful of aux tracks. If the tracks being routed to these ‘sub’ tracks are also linked with the group function it makes it easier to navigiate the mix using faders, solo, mute etc, and it is also a good idea to ‘solo-safe’ each aux track. Here are a couple of images from a recent session which show my sub routing. Notice I also include some parallel compression on the drums and route it to the drum sub aux as well:
When it comes to actually mixing the subs make sure that each individual group is ‘internally’ mixed. Once this is done it saves time giong back to tweak things here and there while mixing the stems. This technique allows each group to be subtly adjusted in volume and panning (if not already panned internally) using single aux tracks.
I first came across this technique during my 3rd year at University when completing my 5.1 surround sound project. My task was to convert a stereo track into 5.1 and before I could do so I had to dismantle the stems so that I could route the individual instruments to the 6 different outputs.
Effects can be added to both the individual tracks and the stems. Personally I prefer to add my plug-ins pre-stem or bus them to separate aux tracks and blend them with the dry ones and reserve the stems purely for volume adjustments. It is all down to preference.