Building a Sidechain Compression Template in Reaper

By Priya Nair · February 23, 2026

Building a Sidechain Compression Template in Reaper

1) What you’ll learn (and why it matters)

Sidechain compression is one of the most practical routing skills you can build in Reaper. It’s how you make a kick drum “push” a bass line out of the way, tame a vocal against loud guitars, or keep a voiceover consistently on top of background music without manually drawing automation for every phrase.

This tutorial walks you through creating a reusable Reaper template that includes:

A clean, repeatable sidechain routing setup
A compressor configured to respond to an external key input
Optional filtering on the detector so the compressor reacts to the right frequencies
Gain-staging and troubleshooting steps so it behaves predictably

The goal is not just “make it duck,” but to build a template that you can drop into real sessions and trust.

2) Prerequisites / setup requirements

Reaper version: Reaper 6.x or 7.x (steps assume current routing window and FX behavior)
Plugins: Stock Reaper plugins only (ReaComp, ReaEQ, JS plugins), so this works on any system
Audio material: At minimum, one track to be compressed (e.g., Bass or Music Bed) and one track as the key/trigger (e.g., Kick or Voiceover)
Project settings: Any sample rate is fine; set your project tempo if you want tempo-synced release timing (not required)

Recommended monitoring: Use a master limiter if you’re experimenting aggressively. Sidechain setups can create unexpected peaks when you overdrive makeup gain.

3) Step-by-step: Build the template

Step 1 — Create and name the core tracks

Action: Create two tracks: one for the audio you want to reduce (the “Ducked” track) and one for the trigger (the “Key” track).

How: Insert two tracks and name them clearly:
- Track 1: “BASS (DUCKED)” or “MUSIC BED (DUCKED)”
- Track 2: “KICK (KEY)” or “VO (KEY)”
Why: Sidechain routing is easy to misread months later. Naming conventions prevent you from compressing the wrong element or sending the wrong signal to the detector.

Common pitfalls: Leaving tracks named “Track 1/Track 2” leads to mistakes when you reuse the template. Also, avoid putting the compressor on the key track—sidechain compression usually lives on the signal being reduced.
Step 2 — Confirm track channel count on the Ducked track

Action: Ensure the Ducked track has at least 4 channels so it can receive an external sidechain on channels 3/4.

How: Click the Ducked track’s I/O button. Set Track channels to 4 (default is 2).

Why: Reaper’s common sidechain method uses channels 1/2 for the audible audio and channels 3/4 as the detector input. If the track only has 2 channels, the sidechain send has nowhere to land.

Common pitfalls: A silent or non-reactive compressor is often just a 2-channel track. If the compressor never gains reduction, check this first.
Step 3 — Route the Key track to the Ducked track’s sidechain channels

Action: Send the Key track to channels 3/4 of the Ducked track, not to the main audible channels.

How (recommended method):
- On the Key track, click I/O.
- Add a Send to the Ducked track.
- In the send settings, set Audio to 1/2 => 3/4.
- Set Send level to 0.0 dB as a starting point.
Why: You want the key signal to control compression without being heard (unless you explicitly want it audible). Sending to 3/4 keeps it separate from your mix path.

Common pitfalls:
- Accidentally using 1/2 => 1/2, which blends the key into the audio and can make your bass track suddenly contain kick drum.
- Using pre-fader vs post-fader sends incorrectly. For most musical ducking, post-fader is fine; for consistent triggering regardless of key track fader moves, switch the send to pre-fader (post-FX).
Step 4 — Insert ReaComp on the Ducked track and select the detector input

Action: Add ReaComp to the Ducked track and tell it to listen to the sidechain channels.

How: On the Ducked track, insert ReaComp (Cockos). In ReaComp:
- Set Detector input to Auxiliary input L+R (this corresponds to channels 3/4).
- Set Auto makeup to OFF (important for predictable gain staging).
- Set Classic attack to ON if you want slightly snappier, more traditional behavior; leave it OFF for a smoother curve. Either is fine—pick one and be consistent in your template.
Why: If ReaComp is listening to the main input instead of the auxiliary detector, you’ll just compress the bass based on the bass itself—which defeats the sidechain purpose.

Common pitfalls: Forgetting to set the detector input is the #1 reason people think sidechaining “doesn’t work.” If you see no gain reduction meter movement during kick hits/VO words, verify this first.
Step 5 — Dial in baseline compression settings (musical ducking starting point)

Action: Use proven starting values that work in real sessions, then adjust by ear.

Starting settings for kick->bass ducking (EDM/pop):
- Ratio: 4:1
- Attack: 2.0 ms (fast enough to clear space immediately)
- Release: 120 ms (musical and commonly stable; adjust to tempo)
- Knee size: 3.0 dB (slightly softer grab)
- Pre-comp: 0.0 ms (leave off initially; use later if needed)
- Threshold: Start around -24 dB, then move until you see ~3–6 dB gain reduction on each kick
Starting settings for voiceover->music bed ducking (broadcast/podcast):
- Ratio: 2.5:1
- Attack: 10 ms (preserves consonant clarity in the music, avoids “choking”)
- Release: 250 ms (smooth recovery between phrases)
- Knee size: 6.0 dB (gentler transitions)
- Threshold: Adjust for ~6–10 dB gain reduction when the voice is present
Why: Attack controls how quickly space is created; release controls how naturally the music/bass returns. Too fast a release causes pumping/chatter; too slow a release makes the bed stay down too long and feel disconnected.

Common pitfalls:
- Over-ducking: 12–20 dB reduction might sound impressive soloed but usually feels like the mix collapses on every kick/word.
- Release too short: You’ll hear a “flutter” or distortion-like pumping, especially on sustained bass notes.
- Auto makeup on: This often counteracts your ducking by boosting output when the compressor works.
Step 6 — Shape what triggers the compressor (sidechain filtering)

Action: Filter the detector so the compressor responds to the most relevant part of the key signal.

How (inside ReaComp):
- Enable ReaComp’s highpass filter in the detector section and set it to 80 Hz for voiceover triggers (removes plosives so “P” pops don’t slam the bed).
- For kick triggers, try a lowpass around 200 Hz so cymbal bleed or clicky beater noise doesn’t cause extra ducking.
Why: The cleanest sidechain behavior happens when the detector hears a simplified version of the key. For VO, plosives can cause exaggerated dips. For kick, high-frequency click can create twitchy, inconsistent reduction.

Common pitfalls: Over-filtering can make the detector miss the transient, forcing you to lower the threshold too far and increasing noise or sensitivity to unrelated content.
Step 7 — Set the key send level and stabilize behavior across sections

Action: Adjust the send level so the compressor reacts consistently even if the key track level changes in the mix.

How:
- On the Key->Ducked send, start at 0.0 dB.
- If the gain reduction is too heavy even with a reasonable threshold, reduce the send to -6.0 dB.
- If it barely triggers, raise the send to +3.0 dB (avoid going much higher; fix the threshold first).
- If you want ducking to stay consistent even when you ride the Key fader, set the send to pre-fader (post-FX).
Why: Treat the key send like a “detector calibration.” The mix fader is for listening balance; the send level is for how strongly the compressor gets triggered.

Common pitfalls: Mixing with the key track fader and unknowingly changing ducking depth. If your ducking changes every time you adjust the key level, switch to pre-fader sends.
Step 8 — Build it into a reusable template (track template + folder option)

Action: Save the setup so you can recall it instantly on new sessions.

How:
- Select both tracks (Key and Ducked).
- Right-click a track panel and choose Save tracks as track template…
- Name it clearly, e.g., “SC Ducking - Key to Ducked (ReaComp)”.
Optional (for bigger sessions): Put the Key and Ducked tracks into a folder named “SIDECHAIN DUCKING”. This makes it easy to collapse/expand and keeps routing organized in dense mixes.

Why: Sidechain routing is repeatable but easy to mess up under deadline pressure. A template turns it into a one-click decision.

Common pitfalls: Saving only the compressor FX but not the routing. Track templates capture routing; FX chains alone won’t store the send mapping.
Step 9 — Troubleshooting checklist (when it doesn’t work)

Action: Use a fast diagnostic path instead of randomly changing knobs.

If you get no gain reduction at all:
- Confirm Ducked track has 4 channels.
- Confirm send is 1/2 => 3/4 (not 1/2 => 1/2).
- Confirm ReaComp Detector input = Auxiliary input L+R.
- Lower threshold to something extreme temporarily (e.g., -40 dB) to verify it can trigger.
If the key bleeds into the Ducked audio (you hear the kick/VO in the bass/bed):
- Your send is probably going to 1/2. Set it back to 3/4.
- Check that you didn’t accidentally create a normal audible send to the Ducked track.
If it pumps or chatters:
- Increase release (try +50 to +150 ms).
- Soften the action with a bigger knee (try 6 dB).
- Filter the detector (HPF for VO, LPF for kick) to remove trigger junk.

4) Before/after: what you should hear and see

Before (no sidechain): The bass and kick compete in the same low-frequency space. The kick feels smaller, the bass feels inconsistent, and you may find yourself turning one down too far. In voiceover scenarios, the music bed masks intelligibility and you end up over-EQ’ing the bed or pushing the VO too loud.

After (sidechain template engaged):

Kick->bass: Each kick transient produces a controlled dip (typically 3–6 dB) in the bass, making the kick read clearly without lowering bass overall level.
VO->music: The music bed gently ducks under speech (often 6–10 dB during phrases) and returns smoothly between lines, improving intelligibility without sounding like the bed is “muting.”

Meter check: ReaComp’s gain reduction meter should move reliably on each key event. If it barely twitches or stays pinned, your threshold/send level/release timing needs adjustment.

5) Pro tips to take it further

Tempo-match release for musical pumping: If you want rhythmic movement, set release so the gain recovers in time with the track. As a starting point at 120 BPM, try 125 ms (roughly a 1/16 note) or 250 ms (roughly an 1/8 note). Fine-tune by ear until the return feels like part of the groove.
Use a “ghost” key for cleaner triggering: Duplicate the kick to a new track called KICK (GHOST KEY), high-pass it at 30 Hz, low-pass it at 200 Hz, and use that as the key send. This keeps the sidechain consistent even if the audible kick is heavily processed.
Pre-comp for ultra-tight kick clearance: If the bass still fights the initial kick click, try Pre-comp 2.0–5.0 ms in ReaComp. This makes the compressor “look ahead” slightly so the dip begins right at the transient. Use sparingly—too much can dull the feel.
Multi-target ducking: Send the same key to multiple tracks (pads, reverb returns, bass). Keep each duck amount smaller (e.g., 2–4 dB each) rather than crushing one element by 12 dB.
Sidechain the reverb return, not the dry vocal: For dense mixes, ducking the vocal reverb with the dry vocal as the key keeps the reverb from clouding the words while preserving vocal level. Start with ratio 3:1, attack 5 ms, release 300 ms, and aim for 3–6 dB reduction on phrases.

6) Wrap-up (practice targets)

Build the template once, then practice using it on three common session types: kick/bass in a dance track, voiceover/music for a promo, and vocal/reverb control in a dense pop mix. Each one teaches a different “release feel” and detector filtering approach.

If you can consistently get predictable gain reduction, avoid audible key bleed, and match the release so it feels intentional, you’re past the beginner stage. Save variations of the template (fast EDM, smooth broadcast, reverb duck) and you’ll stop treating sidechain compression like a trick and start using it like a dependable mixing tool.