Sends, Busses, and Parallel Processing

Serial vs. Parallel

These two words describe every routing decision you will make.

Serial: audio passes through effects in sequence. The output of one becomes the input of the next. This is what insert effects on a channel strip do — the signal has no choice but to go through each one in order.

Parallel: a copy of the audio is sent to a separate path. The original continues unaffected. The copy gets processed independently — reverb, compression, delay, whatever — and both the original and the processed copy reach the output, where they blend together.

Why would you want parallel? Because sometimes you need the dry signal to stay intact. Put a reverb directly on a vocal track (serial) and you are choosing between “mostly dry” and “mostly wet” with the plugin’s mix knob. Send a copy to a reverb on a separate channel (parallel) and you get independent control — separate faders, separate EQ, separate everything. The vocal stays clear. The reverb adds space around it. You control each with its own fader.

Sends and Aux Tracks

A send taps a copy of a track’s signal and routes it to a bus. The original signal continues on its normal path. The bus delivers that copy to an aux (auxiliary) channel strip, which is a full channel with its own fader, pan, insert effects, and sends.

To create a send:

1. Click an empty Send slot on the channel strip
2. Choose a bus number (Bus 1, Bus 2, etc.)
3. Logic automatically creates an Aux channel strip for that bus
4. Load effects on the Aux channel strip
5. Adjust the send level knob to control how much signal goes to the bus

The bus is the pipe. The aux is the destination. When you create a send to Bus 1, Logic builds the aux for you — a pipe needs somewhere to go.

Pre-Fader vs. Post-Fader Sends

Click the small Pre/Post label on a send to toggle between two modes.

Post-fader (the default): the send level follows the track’s volume fader. Pull the track down and the send decreases proportionally. This is what you want most of the time. If the vocal gets quieter, you want its reverb to get quieter too — the reverb stays proportional to the source.

Pre-fader: the send level ignores the fader entirely. Even if you pull the track fader all the way down, the send still delivers signal to the bus at whatever level you set it.

Pre-fader is the exception. You will use it for two things: headphone cue mixes (covered below) and creative effects where you want the wet signal to persist after the dry disappears.

Routing a Shared Reverb on a Bus

The classic parallel setup, step by step:

1. Create a send on your vocal track to Bus 1
2. On the Bus 1 Aux channel strip, load a reverb (ChromaVerb, Space Designer, or any reverb plugin)
3. Set the reverb plugin’s mix to 100% wet — the dry signal already comes from the original track, so you do not want the plugin mixing dry back in
4. Adjust the send level to taste
5. Send other tracks to the same Bus 1

That fifth step is the reason this routing exists. One reverb, shared across the mix. Your lead vocal, your backing vocals, your snare — all sending to the same reverb bus at different send levels. They sound like they are in the same room, because they are, virtually. And you control how much reverb each source gets independently.

Compare this to loading a separate reverb on every track (serial). You would have ten instances of the same plugin consuming CPU, each with its own settings to keep consistent. A shared bus gives you one reverb, one set of controls, and per-track dosing through the send levels.

Creating a Headphone Mix with Sends

When recording a musician, they need to hear themselves and the backing track through headphones. But they may want a different balance than what is coming through the monitors — more of their own instrument, less drums, extra click track.

This is a headphone cue mix, and sends are how you build one. Create a bus dedicated to the headphone output. On each track, add a send to that bus at pre-fader (so the headphone mix stays stable even if you adjust faders in the control room). Adjust each send level to create the balance the musician needs. Route the aux output to whatever hardware output feeds the headphone amp.

The musician hears their custom mix. You hear yours. Everyone is happy.

Track Stacks as Routing Tools

Logic has two kinds of track stacks, and they work differently.

A Folder Stack is purely organizational. It nests tracks visually but does not change their routing. Each track inside still sends its output wherever it was going — usually Stereo Output. The folder is a drawer, not a pipe.

A Summing Stack creates an aux channel and routes every track inside to it. The aux becomes a submix fader — one control for the combined volume, and a place to add processing to the group. This is identical to manually routing multiple tracks to a bus, but Logic sets it up for you and shows it as a collapsible stack in the Tracks area.

Use summing stacks when you want to group tracks for both organization and routing. Use folder stacks when you just want to tidy up the screen.

Groups vs. Routing

This distinction confuses people because both involve controlling multiple tracks together, but they do fundamentally different things.

Routing (busses, sends, summing stacks) is about where audio goes. Multiple signals flowing through a shared pipe. Change the fader on the bus and you change the combined volume. But the individual tracks still have their own faders, their own effects, their own independent controls.

Groups are about synchronized behavior. Put five tracks in a group and when you move one fader, the others follow. When you solo one, they all solo. When you mute one, they all mute. The audio is not combined — each track still goes to its own output. The controls are linked.

Groups are synchronized swimmers. Routing is a shared pipe.

Creating a Group

Select the tracks you want to group, then right-click a track header and choose Create Track Group, or use the Group slot in the Mixer. The Group Settings window lets you choose which parameters are linked: volume, pan, mute, solo, sends, automation mode, record enable, and more. You do not have to link everything — pick what makes sense for your situation.

Group Clutch

Sometimes you need to adjust one track in a group without the others following. Hold Control + Shift (the default for Toggle Group Clutch) while making your adjustment. This temporarily disengages the group link. Release it and the group resumes synchronized behavior.

Group Recording for Multi-Track Sessions

Groups become critical when recording multi-track sources like a drum kit with eight microphones. Enable Record as a linked parameter in the group, and arming one drum track arms them all. Every mic starts and stops recording together.

But groups matter even more for editing multi-track recordings. If you cut one drum track — say, trimming the intro — every mic in the group must cut at the same point. If you comp one take from a take folder, the grouped tracks must follow. Without groups, you would end up with the snare from take 2 playing against the overheads from take 3. The phase relationships would be destroyed and the drums would sound wrong.

This is why groups exist: to keep related tracks moving as a unit. Routing gets them to the same place. Groups keep their behavior in sync.

What to Practice

• Create a send on any track to Bus 1. Open the Mixer and find the Aux channel strip Logic created. Load a reverb on the aux and set it to 100% wet. Adjust the send level on the original track and listen to the blend change.
• Send a second track to the same Bus 1. Both tracks share the reverb. Adjust each track’s send level independently — one gets more reverb, one gets less, but they share the same space.
• Try the pre/post distinction: with a post-fader send to a reverb bus, pull the track fader down and hear the reverb tail disappear with it. Switch the send to pre-fader, pull the fader down again, and hear the reverb persist.
• Add an EQ to your reverb aux channel strip. Roll off everything below 200 Hz. The reverb cleans up without affecting the dry signal — this is something you can only do with parallel routing.
• Select three or four tracks and create a group. Move one fader and watch the others follow. Try the group clutch (default Control + Shift) to adjust one track independently.
• Create a summing stack from a few tracks. Notice the aux that appears. Compare this to a folder stack, which does not create an aux or change routing.

Commands in This Chapter