How to Sidechain in Pro Tools: Key Input, Dyn3 Compressor and Fixes

To sidechain in Pro Tools, send the kick to a bus, insert a compressor such as Dyn3 Compressor/Limiter on the track you want to duck, choose that bus as the compressor's key input, and turn on External Key. The compressor then turns the bass or pad down every time the kick hits.

The routing takes a minute once you've done it. Below are the steps, the settings to start with, how to set up a ghost kick, and what to check when it doesn't work.

What you need

• A trigger track, usually the kick.
• A target track, the one you want to duck: bass, pad, chords or a reverb return.
• A free bus to carry the kick signal to the compressor's sidechain.
• A compressor with a key input. Pro Tools' stock Dyn3 Compressor/Limiter has one, and so do many AAX compressors from other developers.

How to sidechain in Pro Tools, step by step

1. Create the send. On the kick track, click an empty send slot and choose a bus. Rename the bus something you'll recognize, like Kick Key.
2. Set the send level. Raise the send so the compressor gets a strong signal. The kick still plays through its own output as normal; the send only feeds the sidechain.
3. Insert the compressor. On the target track, click an insert slot and choose Dyn3 Compressor/Limiter from the Dynamics category.
4. Choose the key input. In the header of the plug-in window, open the key input selector (it shows no key input by default) and choose your Kick Key bus.
5. Turn on External Key. In Dyn3's sidechain section, enable External Key. Without it, the compressor keeps listening to its own track and ignores the bus.
6. Dial in the compression. Lower the threshold until the gain-reduction meter shows ducking on each kick, then set ratio, attack and release from the table below.

Sidechain compression settings for Pro Tools

Release is the control that makes it groove. Too short and the level snaps back with a click; too long and the track never recovers before the next kick, so it just sounds quieter. Set it while the full beat plays and watch the meter rise back just before each new kick. For the theory behind these settings in any DAW, see our general sidechain guide.

How to focus the sidechain with Key Listen

Dyn3's sidechain section includes high-pass and low-pass filters for the key signal and a Key Listen button. If the kick sample has a lot of click and you want the ducking to follow only its low thump, turn on Key Listen, lower the low-pass filter until you hear just the low end of the kick, then turn Key Listen off again. The compressor now triggers on the part of the kick that actually clashes with the bass.

How to set up a ghost kick in Pro Tools

A ghost kick is a kick track you never hear that exists only to trigger the sidechain. It's useful when you want ducking during a breakdown with no audible kick, or a pump on a different rhythm than the real drums.

1. Duplicate or create a kick track with the trigger rhythm you want, often steady quarter notes.
2. Set its main output to no output (or an unused bus), so it doesn't reach the mix.
3. Send it to the Kick Key bus with a pre-fader send, so its fader position doesn't matter.
4. Keep or remove the real kick's send depending on whether you want both to trigger the ducking.

Why isn't my sidechain working in Pro Tools?

• External Key is off. The most common cause. The key input is set, but the compressor isn't using it.
• Wrong bus. The send and the key input must use the same bus. Renaming the bus makes this easier to check.
• The send is muted or at minus infinity. Depending on your preferences, new sends can start fully down; raise it.
• The send is post-fader and the kick fader is down. Switch the send to pre-fader in its send window.
• The plugin has no sidechain. If the key input selector is missing or greyed out, the plugin doesn't support sidechain in Pro Tools. Use Dyn3 or another compressor that does.
• Threshold too high. With a quiet key signal, the compressor never reaches threshold. Raise the send or lower the threshold.

Sidechain gating and other uses

The same key input routing works with Pro Tools' Dyn3 Expander/Gate. Key a gate on a pad from a hi-hat or a rhythmic part and the pad opens only when that part plays, which gives you rhythmic chopping that follows a real performance. You can also key a compressor on the music bus from the lead vocal, so the instruments dip slightly whenever the singer is in, a technique common in broadcast and podcast mixing.

A no-routing alternative

If you want the pumping sound without buses and key inputs, a tempo-synced volume shaper does the job on the track itself. Our free Pump plugin is built in AAX format for Pro Tools and locks to the session tempo. The Classic Pump preset ducks on every quarter note with 90% depth, a 55% curve and light smoothing, which is close to a strong kick sidechain.

The difference is what drives it. A sidechain compressor reacts to the actual kick, including any variations in timing or level. Pump follows the tempo grid, so it's perfectly consistent and works even when there's no kick at all. If you haven't installed AAX plugins before, our Pro Tools plugin install guide walks through it.