Tech Tip:The Channel Strip Aux Send
By Dennis Kambury
The Auxiliary Send is a relatively uncomplicated control with just a couple of options. It's also one of the most flexible controls on the channel strip! It's like a mini-mixer built into the channel strip and can be used to send the audio signal to effects processors, monitors, additional headphone mixes, or anything else you can imagine (that can make use of line level audio).
The send level determines the amount of signal sent to the aux bus. It doesn't affect the amount of signal going to the channel fader - it's just tapped off the main channel signal and sent to the aux output. This aux output can then feed an external processor. For example, if you have a reverb program for the overall mix, you can route as much or as little signal from each channel to the reverb - maybe a little for the drums, and a lot for the lead guitar.
Another way to use the aux send is as a separate mix bus for headphones or monitors. Instead of sending the aux output to a reverb, plug it into your monitor amp or headphone distribution system. If you have additional aux sends available, you can provide individualized mixes - more keyboard in the guitarist's monitor so he can hear the chords, or more of the singer's signal in her monitor so she can hear herself above the drums!
I use a pair of aux sends to feed my sampler. Whenever I have a sound or texture I want to capture, I just dial up those aux sends, check the levels at the sampler, and hit the record button.
Pre and post
Many mixers include a pre/post switch. This switch determines where the signal gets tapped from the channel - before the main fader, or after. When this control is set to post, adjusting the level from the channel fader will adjust the amount of signal sent to the aux bus. When the switch is set to pre, the signal sent to the aux bus remains constant, no matter what happens with the channel volume.
For example, if you've got the vocal signal being sent to a reverb, and you fade out the channel, with the switch set to post the reverbed vocal fades out too. If the switch is set to pre, the dry vocal signal will fade out, but the reverbed vocal signal will remain.
In the studio, setting the switch to pre allows the engineer to create a mix for the musician's headphones that isn't affected by the main mix in the control room.
On the bus
There are many applications for the aux bus. Depending on how you use your mixer - live, in the studio, or in a fixed installation, you'll find this mini-mixer a valuable tool in getting great sound. This should give you a good idea of what the channel strip's purpose is - balancing levels, adjusting EQ, and routing the signal. Over the next few weeks, we'll break down the various sections and explore them in detail.