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Compression

Definitions

Threshold:

  • The level (in decibels) at which the compressor starts to reduce the signal's gain.
  • Any signal above this level is compressed.
  • In some compressors, the threshold is fixed and the input gain is increased to push the signal into the threashold.
  • Example: If the threshold is set at -10 dB, only audio signals louder than -10 dB will be compressed.

Ratio:

  • The amount of compression applied to the signal once it exceeds the threshold.
  • Expressed as a ratio (e.g., 4:1).
  • A 4:1 ratio means that for every 4 dB above the threshold, only 1 dB will pass through.

Attack:

  • Definition: The time it takes (in milliseconds) for the compressor to start reducing the signal's gain after it exceeds the threshold.
  • Example: A fast attack (e.g., 1 ms) compresses transients quickly, while a slower attack allows more transient detail.

Release:

  • Definition: The time it takes (in milliseconds or seconds) for the compressor to stop reducing gain once the signal drops below the threshold.
  • Alternative Names: Recovery time.
  • Example: A fast release (e.g., 50 ms) allows the signal to return to normal quickly, while a slow release smooths out the compression effect.

Knee:

  • Definition: Controls how gradually or abruptly the compressor transitions into gain reduction as the signal exceeds the threshold.
    • Hard knee: Abrupt compression.
    • Soft knee: Gradual compression, starting slightly below the threshold.

Mix:

  • Definition: Adjusts the balance between the compressed (processed) and uncompressed (dry) signal.
  • This allows for parallel compression, where some of the original dynamics are retained while still benefiting from compression.
  • Alternative Names: blend, dry/wet control