tags: music mus-407 electroacoustic dynamic-range dynamics

Dynamic Range Processing

• #dynamic-range-processing
  • #key-concepts
  • #types
  • #more-terms--techniques
    • #drp-considerations
    • #attack-hold-release
    • #upwarddownward-compression--expansion
    • #side-chaining
  • #transfer-function-examples

Dynamic range processing transforms the amplitude of [audio signals]. A dynamic range process (DRP) changes a signal's [dynamic range] by altering its [amplitude].

• measuring signal amplitude
• adjusts signal amplitude based on measured value

Measured & processed signals can be the same or different (i.e. there can be distinct source & target signals. see: [Sidechaining])

Applications include:

• maintaining a constant signal level
• increasing the overall level of a mix
• creative [transient] and [envelope] shaping
• [noise] reduction
• preventing clipping/overloading
• [sidechaining] (amplitude following, ducking)

Key Concepts

All forms of DRP rely on an amplitude [threshold].

• determines signal level above or below which DRP take effect, depending on the type of effect

DRPs utilize a detection circuit or detection [algorithm] for tracking signal amplitude, which can track either peak or average signal level

Peak: instantaneous measurement, captures true [waveform] peaks: "no sample left unchecked"

• more applicable for preventing overloading/clipping.

Average: signal values averaged over a time interval, also called RMS ([root-mean-square]) tracking

• sculpting the [dynamic range] of the sound without closely monitoring every single peak or [transient]
• provides a smoother response to a changing input signal

Types

• [Noise gate]
• Compressor ([compression])
• [limiter]
• [expander]
• [Envelope shaper]

More Terms & Techniques

DRP Considerations

DRPs, particularly compressors ([compression]) and [limiter]s, can smear/distort transients

• like all effects, easy to overuse, generally should be applied in moderation
• can be used in extremes for creative effect

DRPs may involve a "look ahead" time to properly anticipate signal levels

• introduces a small delay into processed audio
• can create synchronization issues, but usually automatically or easily managed in DAW context

DRPs generally have more applications in recording/live sound.

In [electroacoustic] [composition], traditional application of DRP is less useful

• composer has complete control over levels during compositional process
• can usually go back and adjust levels as necessary

Attack, Hold, Release

Many DRPs include [envelope] parameters: often attack/release, sometimes hold

Attack determines the amount of time for DRP effect to fully activate. The attack [transient] begins when signal crosses the threshold.

Release determines amount of time for DRP effect to deactivate completely. Release transient begins when level no longer crosses threshold.

Hold will force DRP effect to remain active for a time, regardless of threshold.

• can be exploited for creative transient shaping (used explicitly in envelope shapers)
• useful in noise gates to prevent intermittent signal near threshold

Upward/Downward Compression & Expansion

Typical cases:

• compressors attenuate above a threshold ([compression])
• [expander]s attenuate below a threshold
• both referred to as "downward" compression/expansion

However, it is sometimes possible to set a threshold and amplify signal below it, considered a form of compression.

Likewise, it is possible to boost signal above a threshold - a form of expansion.

This technique is infrequently used:

• upward compression raises the [noise floor]
• upward expansion makes peaks even [louder]

Side-Chaining

See: [Sidechaining]

Transfer Function Examples

All DRP effects can be represented through a [transfer function], a function between an input signal (in [dB]) and an output signal with a processed [amplitude].