Audio Mixer Signal Paths, Routing and Grouping
Much of the mixer’s power lies in its ability to interrupt, route and re-route signals for practical or creative purposes. Each channel strip has a pan control, allowing a sound to be ‘positioned’ between the left and right speakers, replicating instruments’ locations on a (virtual) soundstage.
To achieve this, each channel’s output is divided into two ‘left’ and ‘right’ outputs behind the scenes. If a pan control is set fully left, the right side’s gain will be reduced, and output of the left side will be raised by a certain amount to compensate for the overall drop in level (usually +3dB). This means a stereo sound isn’t truly moved across the stereo field, so an external plugin must be used if you want to truly ‘reposition’ a stereo sound without just turning down one side of it.
Insert slots allow you to place a plugin effect at a certain point in the channel’s signal flow to alter the audio’s characteristics at that point. When positioned pre-fader, the effect will occur before the channel’s volume fader in the signal path, so level changes will not affect the inserted device’s effect. This is the most common insert type and is useful for level-dependent plugins such as compressors, noise gates or distortion.
When a plugin is inserted post-fader, changes to the volume slider’s position affect the input level of that effect. This can be useful, say, if you want a frequency analyser’s display to alter when that channel’s volume is changed. Be aware of this difference, otherwise you may painstakingly tweak a compressor post-fader, then turn up the fader, causing it to be compressed much harder and ruining the effect you carefully dialled in.
By default, each of a mixer’s channels will travel directly to the master output fader, but sometimes it may be more practical to take a group of similar tracks for processing together using one channel strip. Drum elements, for example, are often processed as a whole. Some DAWs can now create a group channel at the click of a mouse, but a more hands-on method is to create a new channel and set its input as the outputs of the tracks you wish to group. The exact method varies from DAW to DAW, so again, break out that manual and read up on it.
Grouping tracks becomes even more flexible when routing groups to other groups. Route ten vocal channels as appropriate to two groups named ‘Lead Vocals’ and ‘Backing Vocals’, then send those two groups to a final ‘Vocals’ group.
Sends and returns
Another feature of a mixing desk is the auxiliary send. This creates a ‘copy’ of your signal either pre- or post-fader, routing as much or as little of it as you wish (controlled by the send knob) to a return channel. This routing can be sent from multiple channels and is commonly used to apply reverb, delay, etc, to a mix.
We could, say, send vocals, guitar and snare to Buss 1 in varying amounts, and set Buss 1 as the input to a new return channel. This channel will play the three elements balanced in relation to the send levels we set.