The center channel is very important in movies. It allows the viewers to experience the frontal soundscape as intended. Even those who are seated off-axis (the majority) can enjoy a healthy channel balance thanks to it. The center channel holds sound and pictures together. It’s no coincidence that the most important component of a soundtrack comes from it: dialogue.
The C channel in music
In case none of the music should be routed to the center channel it would mainly be heard from the side of the screen one is sitting close to. We would feel there is an empty space where the most important actions are taking place. Without the C channel music would give the feeling of being detached from the pictures. It would fight against dialogue and sound effects instead of working along with them. In the worst case scenario not routing some of the music to the C channel can create tiredness in the ears of the audience and even disturb the viewing experience.
From stereo to 3 channels
Not many composers can output music mixed on more than 2 channels from their studios. However, if you are among them you don’t need to give up the 3 channel! Here is a method to trick any mono/stereo DAW into exporting to 3 channels, L, C, and R:
A virtual speaker
The trick at the core of this method is setting up our routing as if we had a virtual center speaker. Let’s see how this can be achieved.
Let’s say you have a mono track of a group of instruments’ mic. You must route it on a stereo bus (enabling you to use the standard left and right pan). The pan must be set completely on the left or completely on the right. Next you have to setup an aux send from the mono track to a second bus, this time monophonic, relative to the center channel and set on pre-fader. In other words we are now using two busses, a stereo for L and R and a mono for C. For clarity you could label the stereo bus “mix.LR” and the related mono subpaths “mix.L” and “mix.R”. Likewise you could name the center channel bus “mix.C”.
Next you have to create 3 mono audio tracks. You can call them “rec mix.L”, “rec mix.C” and “rec mix.R”, routed to the stereo listening system. Their input will be the just created bus channels and the three tracks will be panned respectively all the way to the left, to the center and all the way to the right. Once ready you can record your multi-channel music on these tracks.
You can replicate the above steps to achieve the effect on separate stems. In this case you will call the various bus as “Stemname.LR” with the respective mono subpaths and “Stemname.C”. Likewise you will call the audio tracks as “rec Stemname.L”, “rec Stemname.C” and “rec Stemname.R”. The audio tracks will have as output respectively the “mix.LR” and “mix.C” bus. Also make sure you have input monitoring active on the recording audio tracks at all times.
A couple of examples
Let’s imagine that we have a flute mono track and we want to have it sound in a left-central position. We can achieve that by panning the track entirely to the left and increasing the send gain for the center channel. At this point we can obtain various degrees of positioning by tweaking the main fader and the send gain, going from the extreme left to the exact center. If we wanted to have the same effect on the right channel we would need to follow the same procedure but inverting the panning.
In the case of stereo tracks we will need to split them in separate mono tracks, both routed to the same stem. Let’s say we have a Violins I track and we want to position it between the left and center. We will pan the first track (violins1.L) completely to the left. The second (violins1.R) will have the volume fader all the way down and the send gain to 0 dB.
I suggest using a simple stereo reverb. Sending part of the signal to the center channel (narrowing slightly the L and R panning). I’d then record the input of the reverb separately (before it is effected by the reverb that is). This way once you get to the final mix stage it will be possible to implement a real multi-channel reverb. The stereo reverb will, in other words, be used solely for monitoring purposes, not recorded!
When mixing with headphones the position of the various instruments can result particularly extreme and unnatural. I suggest to narrow the panning of the “rec mix” track a bit for monitoring purposes. This will not affect the recorded stems as they will still retain the original panning.
In case you work on Pro Tools (standard) you will find this template useful: Virtual Center Music Mix by Corelli. Let me know how it works for you don’t hesitate to send suggestions on how to improve it!