An aux send is a fundamental feature found on mixing consoles and audio interfaces that allows a specific amount of signal to be split off from the main path. This parallel path sends audio to an external destination, such as a recording device, a monitor system for performers, or a digital effects processor. Unlike the main mix output, which carries the final stereo image for the audience, an aux send provides a raw or processed duplicate of the sound for secondary uses.
How an Aux Send Works in Signal Flow
The signal flow for an aux send typically occurs before the main fader on the channel strip. This means the level sent to the external destination is independent of the main mix fader. When a technician adjusts the aux send knob, they are determining how much of the pre-fader signal travels to the output bus. This independence is crucial for maintaining consistent monitor levels for musicians, even if the main mix is being adjusted for the audience.
Key Applications in Live Sound and Recording
In live sound reinforcement, aux sends are most commonly used to create monitor mixes. Musicians on stage require a different mix than what the audience hears, often emphasizing vocals or specific instruments. By routing various channels to auxiliary outputs, a monitor engineer can craft a custom blend that allows performers to hear themselves and the band clearly. In recording studios, aux sends are used to group instruments together on bus channels, such as sending all drum tracks to a single compressor to glue the rhythm section together.
Parallel Processing and Effects
A very popular use of aux sends is to apply effects like reverb and delay without destroying the original dry signal. Instead of inserting a plugin directly on the channel, a send is routed to an aux bus that holds the effect plugin. The entire band can then be sent to this bus at varying amounts. This technique keeps the core sound intact while adding a shared sense of space and depth across the mix. It also consumes fewer CPU resources in a digital audio workstation compared to multiple inserts.
Adjusting Levels and Pre vs. Post Fader
Understanding the difference between pre-fader and post-fader sends is essential for effective mixing. A pre-fader send takes the signal before the channel fader, ensuring that the aux output level remains constant regardless of how loud or quiet the main mix fader is. Conversely, a post-fader send takes the signal after the fader, causing the aux level to rise and fall with the main mix. Most modern interfaces allow the user to switch between these modes depending on whether the destination requires a consistent level, like a recording track, or a level that follows the main volume change, like a foldback cue.
Gain Staging and Signal Integrity
When working with aux sends, gain staging is critical to avoid noise and distortion. The output level of the aux send should be matched to the input level of the receiving device. If the aux send is too hot, it can clip the input of the external hardware or software, leading to a poor signal. It is good practice to send a strong, clean signal to the destination so that the operator on the other end has ample headroom to adjust the level further.
Digital Interfaces and Modern Implementation
In today's digital audio interfaces and mixing software, aux sends are often represented as virtual knobs on a screen. These function identically to their analog counterparts but offer greater flexibility. Users can rename them, change their color coding, and assign them to specific groups. Many audio interfaces provide multiple aux outputs, which can be patched into hardware compressors, converters, or back into the interface as additional inputs for re-amping or alternative monitoring.
