Compressor
Module ID: fx.compressor
Category: Effects
Header Color: Purple
The Compressor module
Description
The Compressor reduces the dynamic range of a signal by attenuating loud portions while leaving quiet portions unchanged. This creates a more consistent level, adds punch, and can create distinctive pumping effects.
Inputs
| Port | Signal Type | Description |
|---|---|---|
| Input | Audio (Blue) | Signal to be compressed |
| Sidechain | Audio (Blue) | External signal to control compression (optional) |
Outputs
| Port | Signal Type | Description |
|---|---|---|
| Output | Audio (Blue) | Compressed signal |
| Gain Reduction | Control (Orange) | CV output showing compression amount |
Parameters
| Knob | Range | Default | Description |
|---|---|---|---|
| Threshold | -60 dB to 0 dB | -20 dB | Level above which compression begins |
| Ratio | 1:1 to ∞:1 | 4:1 | How much gain reduction is applied |
| Attack | 0.1 ms - 100 ms | 10 ms | How quickly compression engages |
| Release | 10 ms - 1000 ms | 100 ms | How quickly compression releases |
| Makeup Gain | 0 dB to +24 dB | 0 dB | Level boost after compression |
| Knee | Hard/Soft | Soft | Gradual or abrupt compression onset |
How It Works
- Signal level is measured (or sidechain input if connected)
- When level exceeds Threshold, compression begins
- Ratio determines how much signals above threshold are reduced
- Attack controls how fast compression responds to transients
- Release controls how fast compression recovers
- Makeup Gain compensates for level reduction
Understanding Ratio
- 1:1: No compression (bypass)
- 2:1: For every 2 dB above threshold, only 1 dB passes
- 4:1: For every 4 dB above threshold, only 1 dB passes
- 10:1: Heavy compression
- ∞:1: Limiting (nothing passes above threshold)
Threshold Example
If Threshold = -20 dB and Ratio = 4:1:
- Signal at -30 dB: Unchanged
- Signal at -20 dB: Unchanged (at threshold)
- Signal at -10 dB: Reduced to -17.5 dB
Usage Tips
Gentle Leveling
Smooth out dynamics without obvious compression:
Threshold: -18 dB
Ratio: 2:1
Attack: 20 ms
Release: 200 ms
Knee: Soft
Punchy Drums
Add snap and punch:
Threshold: -10 dB
Ratio: 4:1
Attack: 10 ms
Release: 50 ms
Fast attack catches transients, fast release lets energy through.
Sustained Bass
Even out bass levels:
Threshold: -15 dB
Ratio: 4:1
Attack: 5 ms
Release: 150 ms
Vocal Compression
Consistent vocal level:
Threshold: -20 dB
Ratio: 3:1
Attack: 10 ms
Release: 100 ms
Knee: Soft
Synth Pad Sustain
Make pads sustain more evenly:
Threshold: -24 dB
Ratio: 3:1
Attack: 30 ms
Release: 300 ms
Slow attack preserves natural swell.
Sidechain Pumping
Classic EDM pumping effect:
[Kick] ──> [Compressor Sidechain]
[Pad/Bass] ──> [Compressor Input]
Threshold: -30 dB
Ratio: 6:1
Attack: 1 ms
Release: 200 ms
The kick ducks the pad, creating rhythmic pumping.
Peak Limiting
Catch peaks without obvious compression:
Threshold: -3 dB
Ratio: 10:1 or higher
Attack: 0.1 ms
Release: 50 ms
Parallel Compression
Blend compressed and dry signals:
[Input] ──> [Compressor] ──> [Mixer Ch 2]
──> [Mixer Ch 1 (dry)]
[Mixer] ──> [Output]
Heavy compression (6:1+) on the compressed path, blend to taste.
Using Gain Reduction Output
Visualize or control other parameters based on compression:
[Compressor GR Output] ──> [Other Parameter CV]
Could modulate filter cutoff, pan, effects send, etc.
Attack and Release Guide
Attack Times
| Attack | Effect |
|---|---|
| 0.1-1 ms | Catches all transients (can sound unnatural) |
| 1-10 ms | Fast, punchy, some transients pass |
| 10-30 ms | Balanced, musical compression |
| 30-100 ms | Slow, lets transients through fully |
Release Times
| Release | Effect |
|---|---|
| 10-50 ms | Fast, can cause pumping |
| 50-150 ms | Medium, musical, versatile |
| 150-400 ms | Slow, smooth, sustained |
| 400+ ms | Very slow, sustained compression |
Knee Types
Hard Knee
Compression applies suddenly at threshold. More obvious compression, more aggressive.
Soft Knee
Compression gradually increases around threshold. More transparent, natural sound.
Gain Staging
- Set Threshold to catch peaks you want to compress
- Adjust Ratio for desired amount
- Use Makeup Gain to match bypassed level
- A/B compare with bypass to verify
Connection Examples
Channel Strip
[Synth] ──> [EQ] ──> [Compressor] ──> [Output]
Sidechain Setup
[Kick] ──> [Compressor Sidechain]
[Bass] ──> [Compressor Input]
[Compressor Output] ──> [Output]
Parallel Compression
[Drums] ──> [Compressor (heavy)] ──> [Mixer (wet)]
──> [Mixer (dry)]
[Mixer] ──> [Output]
Ducking
[Voice/Narration] ──> [Compressor Sidechain]
[Background Music] ──> [Compressor] ──> [Output]
Music ducks when voice is present.
Compression Cheat Sheet
| Use Case | Threshold | Ratio | Attack | Release |
|---|---|---|---|---|
| Gentle leveling | -18 dB | 2:1 | 20 ms | 200 ms |
| Punchy drums | -10 dB | 4:1 | 5 ms | 50 ms |
| Sustained bass | -15 dB | 4:1 | 5 ms | 150 ms |
| Vocal control | -20 dB | 3:1 | 10 ms | 100 ms |
| Pad sustain | -24 dB | 3:1 | 30 ms | 300 ms |
| Sidechain pump | -30 dB | 6:1 | 1 ms | 200 ms |
| Peak limiting | -3 dB | 10:1+ | 0.1 ms | 50 ms |
Tips
- Don't overcompress: 2-6 dB of gain reduction is usually enough
- Match levels: Use Makeup Gain to fairly compare compressed vs original
- Attack is key: It determines if transients punch through
- Release affects groove: Too fast causes pumping, too slow causes sustained squash
- Use your ears: Watch meters but trust what sounds good
Related Modules
- VCA - Alternative level control
- EQ - Often used before/after compression
- Distortion - Can add saturation like compressor
- Audio Output - Has built-in limiter