Dynamics Processing

Dynamics in audio signals

Dynamics describe level changes within a signal over time.

Dynamic range is the difference between the highest and lowest relevant levels. The result depends on the signal, measurement, and time scale.

Related: Fundamentals of Sound · Psychoacoustics

Dynamics at different time scales

Microdynamics and macrodynamics

The time scale determines what kind of level change is being controlled.

Dynamics problems and possible controls

Not every uneven passage requires compression.

Manual and automatic level control

Level and dynamic range can be controlled through manual, automatic, and assisted approaches.

• editing and item gain: isolate passages and correct local level differences before processing
• volume automation: shapes phrases, sections, and larger dynamic contours
• compression: reacts automatically to short-term changes in signal level
• assisted tools: generate level rides or propose compressor settings for further adjustment

Downward compression

Compressor parameters

• threshold: level at which compression begins
• ratio: relationship between input and output level changes above the threshold
• attack: how quickly gain reduction responds
• release: how quickly gain reduction returns
• knee: how abruptly or smoothly compression begins around the threshold
• make-up gain: gain applied after compression

Compression ratios

Hard-knee response without make-up gain

Attack and release

• Attack sets how quickly gain reduction reaches its target.
• Release sets how quickly it returns toward zero.

Compressor signal flow

Level detection and gain computation derive a control signal.

• look-ahead briefly delays the audio path so gain reduction can respond before a peak arrives

Evaluating compression

• match the processed and bypassed levels before comparing them
• listen for changes in transients, envelope, rhythm, and background detail
• consider whether the gain reduction supports the intended balance
• evaluate the result within the complete mix as well as in isolation

A louder version may initially seem better, even when the processing itself is not an improvement.

Sidechaining

A sidechain lets one signal control the dynamics processing of another.

• useful for creating space between competing sounds, e.g. kick controls bass

Multiband compression

Multiband compression divides the signal into frequency bands and compresses each band independently.

• useful when dynamic problems are limited to particular frequency bands

Limiting

Upward compression

Expansion

Gating

The loudness war

The loudness war describes the use of heavy compression and limiting to make recordings appear louder.

• excessive processing reduces dynamic contrast and may cause listener fatigue
• loudness normalization reduces the advantage of simply increasing level
• normalization cannot restore dynamics already removed during production

Automation and compression

Use a short recording with clear level changes and distinct transients. Create one controlled version with volume automation and another with compression, then compare them at matched loudness.

Decide which approach better supports the material. Consider transients, low-level detail, and the larger dynamic shape when explaining your choice.

Selected references

• Katz, Bob. Mastering Audio: The Art and the Science. 3rd ed., Focal Press, 2015.
• Giannoulis, Dimitrios, Michael Massberg, and Joshua D. Reiss. “Digital Dynamic Range Compressor Design—A Tutorial and Analysis.” Journal of the Audio Engineering Society, vol. 60, no. 6, 2012, pp. 399–408.

Related: Fundamentals of Sound · Psychoacoustics · Digital Audio