Engineering Tutorial

Compression

Dynamic Control & Tone Shaping

What is Compression?

Compression reduces the dynamic range of audio by making loud parts quieter and (with makeup gain) quiet parts louder. It's the most powerful tool for controlling dynamics, adding punch, glue, and character to your mix.

Think of compression as an automatic volume knob that turns down when the signal gets too loud, then turns back up when it gets quiet.

Why Compression Matters

  • Control Dynamics: Tame wild volume fluctuations in vocals or instruments
  • Add Punch: Emphasize transients and attack for impact
  • Create Glue: Make elements sit together cohesively
  • Increase Loudness: Reduce peaks to allow higher overall levels
  • Shape Tone: Different compressors add unique coloration
  • Enhance Sustain: Bring up quiet tails of notes

Compression Parameters Explained

Threshold

What it does: Sets the level where compression starts

  • Lower threshold = more compression
  • Higher threshold = less compression
  • Set so peaks trigger compression, not the whole signal

Ratio

What it does: How much compression is applied above threshold

  • 2:1 to 4:1: Gentle, transparent compression
  • 4:1 to 8:1: Medium, noticeable compression
  • 8:1 to 20:1: Heavy compression, limiting
  • ∞:1: Hard limiting (brick wall)

Attack

What it does: How quickly compression engages after threshold is crossed

  • Fast (0.1-10ms): Catches transients, reduces punch
  • Medium (10-30ms): Balanced, natural sound
  • Slow (30-100ms+): Lets transients through, adds punch

Release

What it does: How quickly compression stops after signal drops below threshold

  • Fast (50-150ms): Responsive, can sound pumpy
  • Medium (150-300ms): Natural, musical
  • Slow (300ms-2s): Smooth, glue-like
  • Auto: Adapts to the material (often best)

Knee

What it does: How gradually compression engages around threshold

  • Hard knee: Abrupt, precise compression
  • Soft knee: Gradual, smooth, musical

Makeup Gain

What it does: Restores volume lost to compression

  • Match input and output levels for fair comparison
  • Auto makeup gain is convenient but check manually

Step-by-Step Compression

1. Set Your Threshold

  • Start with threshold high (no compression)
  • Lower it until you see 3-6dB of gain reduction on peaks
  • More GR isn't always better—start subtle

2. Choose Your Ratio

  • Vocals: 3:1 to 6:1
  • Drums: 4:1 to 10:1
  • Bass: 4:1 to 8:1
  • Mix bus: 2:1 to 4:1

3. Adjust Attack

  • Want punch? Use slow attack (30-50ms)
  • Want control? Use fast attack (1-10ms)
  • Listen to how it affects the transient

4. Set Release

  • Start with auto release if available
  • Or match release to the tempo/rhythm
  • Too fast = pumping, too slow = sluggish

5. Add Makeup Gain

  • Match output to input level
  • A/B at equal loudness
  • Louder always sounds "better"—don't be fooled

Example Settings

Rap Vocals (Aggressive)

  • Threshold: -20dB (4-6dB GR)
  • Ratio: 4:1
  • Attack: 5-10ms (fast)
  • Release: Auto or 100-200ms
  • Knee: Medium

Sung Vocals (Natural)

  • Threshold: -18dB (3-5dB GR)
  • Ratio: 3:1
  • Attack: 10-30ms (medium)
  • Release: Auto or 150-300ms
  • Knee: Soft

Kick Drum (Punch)

  • Threshold: -15dB (6-10dB GR)
  • Ratio: 6:1
  • Attack: 20-40ms (slow, let transient through)
  • Release: 100-200ms (fast)
  • Knee: Hard

Snare (Control)

  • Threshold: -12dB (4-8dB GR)
  • Ratio: 5:1
  • Attack: 1-5ms (fast)
  • Release: 50-150ms (fast)
  • Knee: Medium

Bass Guitar

  • Threshold: -20dB (4-6dB GR)
  • Ratio: 4:1
  • Attack: 10-20ms (medium)
  • Release: Auto or 200-400ms
  • Knee: Soft

Mix Bus (Glue)

  • Threshold: -10dB (1-3dB GR)
  • Ratio: 2:1 to 3:1
  • Attack: 30ms (slow)
  • Release: Auto or 300-500ms
  • Knee: Soft

Compression Techniques

Parallel Compression

Blend compressed and uncompressed signals for punch + dynamics.

  • Send to aux with heavy compression (8:1, fast attack)
  • Blend compressed signal under original (30-50%)
  • Keeps transients while adding body and sustain

Serial Compression

Multiple compressors in series, each doing light work.

  • First: 3:1, 2-3dB GR (control peaks)
  • Second: 2:1, 1-2dB GR (add glue)
  • More transparent than one heavy compressor

Sidechain Compression

Trigger compression from an external source.

  • Duck bass when kick hits (EDM/hip hop)
  • Duck music when vocals come in (podcasts)
  • Create pumping effect (EDM)

Multiband Compression

Compress different frequency ranges independently.

  • Control boomy low-end without affecting highs
  • Tame harsh highs without dulling the mix
  • Essential for mastering

Common Mistakes

  • Too much gain reduction: 10dB+ GR kills dynamics and sounds squashed
  • Fast attack on everything: Removes punch and transients
  • Not using makeup gain: Can't judge if compression is helping
  • Compressing in solo: Sounds good alone, disappears in mix
  • Ignoring the meter: Watch GR meter, not just your ears
  • One-size-fits-all settings: Every source needs different compression
  • Compressing to fix EQ problems: EQ first, compress second

Pro Tips

  • Less is more: 3-6dB GR is usually plenty
  • Match levels when A/B: Compression makes things louder—compensate
  • Use your ears: If it sounds good, it is good
  • Compress after EQ: Clean signal = better compression
  • Try different compressors: Each has unique character (1176, LA-2A, SSL)
  • Automate instead: Sometimes manual volume rides work better
  • Check in context: Solo to set, mix to confirm
  • Save presets: Build a library of go-to settings

Compressor Types

VCA (Voltage Controlled Amplifier)

Sound: Clean, precise, punchy

Use for: Drums, bass, mix bus (SSL-style)

FET (Field Effect Transistor)

Sound: Fast, aggressive, colorful

Use for: Vocals, drums, anything needing attitude (1176)

Optical (Opto)

Sound: Smooth, musical, slow

Use for: Vocals, bass, mix bus (LA-2A, LA-3A)

Tube/Variable-Mu

Sound: Warm, smooth, vintage

Use for: Mix bus, mastering, vocals (Fairchild, Manley)

Digital

Sound: Clean, transparent, flexible

Use for: Anything requiring precision and control

Genre-Specific Compression

Hip Hop

Heavy, aggressive compression. Vocals: 4:1-6:1, fast attack. Drums: parallel compression for punch. 808s: light compression to control peaks.

Rock

Medium compression for energy. Drums: 4:1-6:1, medium attack. Vocals: 3:1-4:1, preserve dynamics. Mix bus: 2:1-3:1 for glue.

EDM

Heavy compression and limiting. Sidechain everything to kick. Parallel compression on drums. Multiband on master for loudness.

Jazz

Minimal, transparent compression. 2:1-3:1 ratios, slow attack to preserve dynamics. Focus on natural performance, not control.

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