Question about attack and release times in (ms)

[sleepwalker]

On a typical software compressor what do the specific ms values of the attack and release control do?

Say the attack is 10ms and the release is 50ms. Does the compressor trigger exactly 10ms after the threshold is reached? Does it release exactly 50ms after the threshold value reaches "false"?

Or

Does the compressor use the full 10ms to variably compress the signal, reaching the full chosen ratio at 10ms. Likewise, the 50ms release is the period of time it takes to go from full compression to no compression.

Hope I've made myself clear.
Thanks,
Dan

[Tim Farrant]

Good question. Unless the spec includes some sort of reference to the actual gain reduction occurring, then it's meaningless. For example, if the attack and release times are specified relative to 10dB of gain reduction, then you can say "the compressor will take 5mS to attack from 0 to -10dB (gain reduction) and take 100mS to release back to 0". A better way to specify attack and release times is mS/dB. In the above example, the attack time is 0.5mS per decibel (0.5mS/dB) and the release time is 10mS/dB.

Make sense?

Cheers
Tim.

[Bob Olhsson]

To be honest, I've never observed any correlation in attack and release settings between different limiters or compressors in hardware or software.

[alphajerk]

technically, they COULD write the cod ethat it does it in such a way... they already add variable knee. a "slew rate" function might be nice. there are hold functions on some.

i always though plugins should function like the ADSR envelopes in synths... all with bezier curves on each point. total fine tuning of the action of the compressor with visual feedback.

[Ethan Winer]

Dan,

> Does the compressor use the full 10ms to variably compress the signal, reaching the full chosen ratio at 10ms. Likewise, the 50ms release is the period of time it takes to go from full compression to no compression. <

Yes, that's the right one.

Originally, all compressors were made from analog circuits, and the attack and release times were determined by the time constant of a resistor and capacitor. So the attack time is how long it takes to reduce the gain by the appropriate amount depending on the input level and threshold setting. Same for the release time after the signal drops below the threshold. Further, if the changes were instantaneous, you'd get a loud click every time the volume were lowered and raised.

Digital compressors work exactly the same way, but use code to emulate what an analog compressor does.

--Ethan

[inaudio]

To be honest, I've never observed any correlation in attack and release settings between different limiters or compressors in hardware or software.

- Bob O.

This is why I love the 1176 calibration - no numbers on the face at all! Gotta use ears.

<L>

[sleepwalker]

Thanks for the comments guys. I appreciate it