Compression Below the Threshold

This was a question in a foum:

Please confirm if this statement is true or not “the compression still works and compresses even when the signal falls below the threshold”. If not… I don’t see why release would be doing anything to the signal…
if yes please further explain so I can understand.

An image was then provided which made little sense as it is was not annotated in any way. Another person drew a line to represent the most likely Threshold.

Compress Legend
Compress Legend

I then added points and this explanation:

If Threshold were at the Red Line as seems reasonable (one wonders why the image has no guide/legend) then it seems to me that:

  1. Audio is playing below Threshold unmolested by the Compression
  2. A sudden loud signal appears
  3. The Attack phase gets underway and
  4. Clamps to its Ratio – assuming 2:1
  5. Loud signal suddenly stops – falls below Threshold
  6. The Compressor is still in for every 2db in, let 1db out mode
  7. This will keep going until the Release phase finishes (in a nice linear fashion it appears)

As a result, the sudden “offness” of the signal catches the slow Compressor by surprise (all machines can only ever work on what has happened – which is why automatic cars can’t change down before a hill gets steep) so it can actually “bite” below the Threshold in such a case.

This is a somewhat rare case as few instruments are that ON/OFF. Also, you may decide to shorten the release of the Compressinaor.

The workings of Compression seem nonsensical a lot of the time, but this is more to do with our thinking than that of compressors. Compression is pure logic, only it behaves in a machine style of thinking which is not the same style of fuzzy thinking we humans prefer (I want it to be therefore it is – or should be).

More importantly, there is the psychoacoustics of the situation where a sudden LOUD sound will cause the human brain to do this very thing you see here as it “flinches” and takes a moment to recover and open its eyes (ears) again. During that time, the world is actually muted to some extent.

This last is where Compression truly gets interesting and becomes your friend in Storytelling as you can use compressors (and their various relatives) to not just “flatten” dynamics but shape them to better express the story of one sound, a section, or the whole track.

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