An aux send is a fundamental feature found on nearly every mixing console, audio interface, and digital audio workstation that allows a specific amount of signal to be split off from a channel and routed elsewhere. This routing happens before the channel fader, meaning the level of the aux send is independent of the main output level, providing a clean way to feed external processors or monitor systems without affecting the core mix. Understanding this signal path is essential for anyone looking to move beyond basic playback and capture scenarios.
Breaking Down the Signal Path
The core of an aux send resides in the pre-fader circuit of the audio channel. Because the send is taken before the channel’s main fader, adjusting the master output does not alter the intensity of the signal sent to the aux bus. This behavior is critical for maintaining consistent monitoring levels or applying effects regardless of how loud or quiet the performer is in the main mix. The send level is usually controlled by a physical knob or a digital trim pot, allowing the user to set the ratio of the original signal that gets diverted.
Parallel Processing: The Heart of Modern Mixing
One of the most powerful applications of an aux send is parallel processing, where a dry (unprocessed) signal is blended with a heavily processed version of the same signal. Engineers often use aux sends to route audio to compressors, saturators, or exciters to add glue, punch, or harmonic richness without destroying the original transients. By blending the processed signal with the clean original on the aux return, you achieve a sound that is energetic and polished while retaining the natural dynamics of the source.
Common Parallel Processing Examples
Drum Bus Parallel Compression: Adding sustain and impact to a drum kit.
Vocal Bus Saturation: Introducing subtle warmth and glue to a lead vocal chain.
Master Bus Excitement: Enhancing the overall presence and loudness of a mix.
Creating Monitor Mixes for Performers
In live sound and studio monitoring, aux sends are the backbone of creating custom mixdowns for artists on stage or in the control room. Musicians often require a different balance of instruments in their headphones or stage monitors than what the main audience hears. By routing specific channels to dedicated aux buses, the engineer can create a "mix minus" feed, which removes the performer’s own microphone from their monitor to prevent feedback. This allows the artist to hear the rest of the band and the click track clearly without the distracting bleed of their own voice.
Sends vs. Inserts: Understanding the Difference
It is vital to distinguish between an aux send and an insert to use them effectively. An insert sends the entire signal of the channel down a singular path where it is processed completely before returning, effectively removing it from the main mix until the insert returns. In contrast, an aux send splits the signal, allowing the original channel to remain dominant while sending a portion to an external effect or monitor. Think of inserts as a direct pipeline for heavy processing and aux sends as a branching road for supplementary treatment.
Routing for Effects and Spatial Processing
Reverb and delay are the quintessential effects handled via aux sends, and for good reason. Sending multiple vocal or instrumental tracks to a single aux return of the same reverb unit ensures that the spatial parameters—such as decay time and pre-delay—remain consistent across the entire mix. This technique creates a cohesive soundstage where all elements exist in the same physical space. If you were to insert a reverb directly on every track, you would fight against phase cancellation and struggle to maintain a unified ambient environment.
