Audio Compression Techniques

Why This Matters

Compression is arguably the most powerful—and most misunderstood—tool in your production arsenal. It's not just about making things louder; it's about controlling dynamics to create clarity, punch, and cohesion in your mixes. Whether you're taming an unruly vocal performance, adding sustain to a snare, or gluing an entire mix together, compression shapes how listeners feel the energy of your music. Understanding these techniques separates amateur mixes from professional ones.

You're being tested on more than just knowing what a threshold does—you need to understand how compression parameters interact, when to use different compression types, and why certain settings work for specific sources. The concepts here connect to broader principles of gain staging, frequency management, signal flow, and psychoacoustics. Don't just memorize definitions—know what problem each technique solves and when you'd reach for it in a real session.

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Core Compression Parameters

These are the fundamental controls found on virtually every compressor. Mastering these parameters is essential before moving to advanced techniques—they determine how aggressively, quickly, and transparently your compressor responds to incoming signal.

Threshold

• Sets the level where compression begins—any signal above this point gets reduced according to your ratio setting
• Lower threshold = more compression—you're essentially telling the compressor to work on a larger portion of the signal
• Critical for gain staging—setting this correctly ensures you're compressing the right dynamic peaks without squashing everything

Ratio

• Determines compression intensity—expressed as input:output (e.g., 4:1 means 4dB over threshold becomes 1dB over)
• Gentle ratios (2:1–4:1) work for transparent leveling; aggressive ratios (8:1+) create obvious dynamic control
• Directly affects dynamic range—higher ratios narrow the gap between loud and soft, fundamentally changing the signal's character

Makeup Gain

• Restores output level after compression—compensates for the volume reduction caused by gain reduction
• Essential for A/B comparison—without matching levels, you'll mistake "louder" for "better" when bypassing
• Not just about loudness—proper makeup gain lets you hear what the compression is actually doing to the sound

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Timing Controls

Attack and release settings determine the temporal behavior of compression—how the compressor breathes with your music. These parameters have the most dramatic impact on the feel and punch of your tracks.

Attack Time

• Controls response speed after threshold is crossed—measured in milliseconds (ms)
• Fast attack (1–10ms) catches transients, reducing punch; slow attack (30–100ms+) lets transients through, preserving impact
• Critical for drums and percussion—the difference between a snare that snaps and one that thuds often comes down to attack time

Release Time

• Dictates how quickly compression stops after signal drops below threshold—affects the "recovery" of your sound
• Fast release creates pumping/breathing effects; slow release provides smoother, more transparent compression
• Must match the tempo and groove—release times that fight the rhythm create unmusical artifacts

Knee (Soft vs. Hard)

• Determines the transition curve into compression—hard knee engages abruptly at threshold, soft knee introduces compression gradually
• Hard knee = more aggressive and obvious; soft knee = more musical and transparent
• Soft knee effectively lowers the threshold slightly—compression begins gently before the set threshold, then increases progressively

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Advanced Compression Types

Beyond standard compression, these techniques offer specialized control for complex mixing situations. Each solves a specific problem that basic compression can't address effectively.

Parallel Compression

• Blends compressed and dry signals together—also called "New York compression," originally popularized on drums
• Preserves transients while adding density—you get the punch of the original plus the sustain and fullness of heavy compression
• Set up via aux send or duplicate track—compress the parallel channel aggressively (high ratio, fast attack) and blend to taste

Sidechain Compression

• Uses one signal to trigger compression on another—the "key" or "trigger" input controls gain reduction on the main signal
• Creates the iconic EDM "pumping" effect—kick drum triggers compression on synths/bass, making them duck rhythmically
• Essential for frequency management—duck bass when kick hits to prevent low-end mud without cutting frequencies permanently

Multiband Compression

• Splits signal into frequency bands with independent compression—typically 3–5 bands (lows, low-mids, high-mids, highs)
• Allows surgical dynamic control—tame a boomy low-end without affecting crisp highs, or control harsh mids independently
• Powerful but dangerous—overuse can create an unnatural, "split" sound; use sparingly and check in mono

Limiting

• Extreme compression with very high ratios (10:1 to ∞:1)—acts as a "brick wall" ceiling that signal cannot exceed
• Prevents clipping and enables loudness maximization—essential in mastering for competitive levels
• Introduces distortion when pushed hard—understand the trade-off between loudness and dynamic integrity

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Compression Direction and Behavior

Understanding which way compression works opens up creative possibilities beyond simple peak reduction. Downward compression is standard, but upward compression and expansion offer different solutions.

Downward Compression

• Reduces loud signals above the threshold—the standard compression behavior most producers know
• Decreases dynamic range from the top down—loud parts get quieter, bringing them closer to soft parts
• Best for controlling peaks and evening out performances—the go-to for vocals, bass, and most mixing applications

Upward Compression

• Boosts quiet signals below the threshold—the opposite of standard compression, raising the noise floor
• Increases audibility of subtle details—room tone, breath, decay tails all become more prominent
• Useful for adding sustain and presence—can make drums sound bigger without squashing transients

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Application-Specific Techniques

Compression settings must be tailored to the source material. What works for a vocal will destroy a drum bus, and vice versa—context is everything.

Compression for Vocals

• Consistent intelligibility is the goal—vocals must sit clearly in the mix without disappearing or overpowering
• Medium attack (10–30ms) preserves consonants; medium release (50–100ms) follows natural phrasing
• Often requires multiple stages—gentle compression for leveling, followed by more aggressive compression for character

Compression for Drums and Percussion

• Attack time is critical for punch—slow attack lets the transient snap through; fast attack creates a "thick" sound
• Release should match groove—time it so the compressor recovers before the next hit for consistent dynamics
• Parallel compression excels here—blend heavily compressed signal for weight while keeping original transients intact

Mixing vs. Mastering Compression

• Mixing compression shapes individual elements—focused on balance, tone, and making tracks sit together
• Mastering compression glues the entire mix—subtle settings (1–3dB gain reduction) for cohesion and loudness
• Different tools for different jobs—mixing uses surgical precision; mastering uses broad, gentle strokes

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Troubleshooting and Quality Control

Knowing what can go wrong is just as important as knowing what to do. Over-compression is one of the most common mixing mistakes—learn to identify and avoid these artifacts.

Compression Artifacts and Distortion

• Pumping occurs when release is too fast—you hear the compressor "breathing" as it rapidly engages and disengages
• Breathing/noise floor rise happens with too much gain reduction—quiet sounds between phrases become audible
• Distortion results from excessive limiting or fast attack on transient-heavy material—the compressor can't respond cleanly

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Quick Reference Table

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Self-Check Questions

1. Compare and contrast parallel compression and multiband compression—what problem does each solve, and when would you choose one over the other?

2. Which two parameters most directly affect whether a compressor preserves or reduces the "punch" of a drum hit? Explain how their interaction shapes the transient.

3. You're mixing a vocal that sounds "pumpy" and unnatural. Which compression parameters would you adjust, and in what direction?

4. Identify the key differences between compression used in mixing versus mastering. What gain reduction amounts and ratio settings are typical for each context?

5. A producer wants the bass to "duck" when the kick drum hits in an EDM track. Which compression technique achieves this, and what signal would serve as the trigger input?