Advanced Mixing: Buses, Sends, and Ducking

Basic mixing balances tracks against each other one at a time. Advanced mixing is about controlling groups of tracks together, efficiently, using routing.

What a bus actually does

A bus (or aux track) is a shared channel that multiple tracks route through together. Instead of processing five backing vocal tracks individually, you route all five to one "Backing Vocals" bus and apply compression or EQ once, to the group — it's faster, and it makes the group glue together more cohesively than processing each one separately.

Setting up a bus

Create a new Audio track to act as your bus, then use each source track's output routing option to send its signal to that bus instead of (or in addition to) the master output. Group related tracks — all drum tracks, all backing vocals, all synth layers — onto their own bus for combined control.

Sends: sharing one effect across many tracks

A send routes a copy of a track's signal to a shared effect — most commonly reverb — without moving the track's main signal off its own channel. This is both more efficient (one reverb instance instead of ten) and often sounds better, since everything sent to the same reverb shares the same sense of space, like instruments actually recorded in the same room.

Adjust how much of each track goes to the send individually — a vocal might go heavily into the shared reverb while a kick drum barely touches it at all.

Ducking with automation

Ducking temporarily lowers one track's volume in response to another — classically, music dropping slightly under narration or a lead vocal. Without a dedicated sidechain feature, you recreate this in GarageBand with manual volume automation: draw dips into the background track's automation lane that line up exactly with the phrases of the part you want to stand out.

This technique is especially useful for podcasts (music under speech) and for carving space for a lead vocal during busy, dense sections of a song.

Building a mix in stages

An efficient advanced mixing order:

1. Balance levels within each bus group first (all drums against each other, for example).
2. Balance bus groups against each other (drums vs. vocals vs. instruments).
3. Set up shared sends (reverb, delay) once groups are balanced.
4. Add ducking automation for any parts competing for the same space.
5. Do a final pass on the overall master bus.

What's next

With your mix properly routed and balanced, the next lesson covers advanced automation — the moves that make a mix feel dynamic and intentional from start to finish, not just correctly balanced.