MD Tip: Compression & Limiting

Here's an excerpt from several of my threads, along with responses from some forum members...

A simple explanation of the Compression Ratio:

Given a 3:1 ratio, for every 3dB the signal exceeds the threshold level you have set, only 1dB of signal will pass (over and above the threshold level). ---jonrose

In other words, using 3:1, where 3=x and 1=y. What this means is that, for every X dB above threshold, the signal is Y dB at the output. So what's the difference between compression and limiting? Simply, compressing occurs with ratios below 10:1...limiting occurs with ratios above 10:1 (ie, 20:1, 30:1, infinity:1, etc)

Now, how about setting these parameters? Are there defaults that should be used? Here's some answers that might help...

THRESHOLD. This is totally dependent on the recorded level of the instrument in question. Going above the threshold is the point where compression begins. Having a default of -10 is fine, IF each and every time you record said instrument with the same levels (peak, what have you, etc)...Thresholds often need to be altered to accomodate the source recording's level

RATIO: Well, this is a bit easier to make a default out of. Again, it's about hearing what's happening to the signal when it goes above threshold, and what you're trying to achieve. Punch and Tightening can be achieved with as little as 1.75:1, 2:1, even 3:1...Beyond that, punch is not really the effect, as much as dynamic control.

ATTACK/RELEASE: Again, here's an area where listening is key. For instance, many people set a default A/R for snare drums, roughly 20ms attack and 100ms release. Fine. But, again, depending on threshold level and HOW the drums were played (and the style of the tune) a 20ms attack might be too fast, causing audible 'clicks' when the snare is hit. Backing off a few MS (ie, 25ms) will allow you to retain the transient and beef it up, without the 'clipped' sound of the attack. The release is much more dependent on the speed of the playing as well. For a fast tune, you no doubt want a fast release. For a warm-ballad, a slower release will give you a thicker, phatter snare sound.

OUTPUT COMPENSATION GAIN: This field can be your friend. If you've set your compressor properly, it's likely that the output of your file has been somewhat attenuated. Use this field to 'make up' for gain lost in the process (on some hardware devices, this control is actually titled 'Make-Up Gain')

---Audition M.D.

From SteveG, a little bit on Peak and RMS detection settings...

Peak or RMS? The difference is all to do with how the compressor responds to the 'loudness envelope' of your track. Peak says 'okay, there's a very high, but short transient there, so I'll use that as the reference point for the amount of compression I'm going to apply at this instant'. RMS (stands for Root of the Mean (value) Squared) effectively looks at the 'perceived loudness' values of the track and uses those to set the compression value. By and large, RMS is the one to use, as it does more or less what your ears do. Synt says that the Peak setting was only there to ensure backwards compatibility. Peak can be difficult, as it appears to do about twice as much as you think it should!

SteveG's String Line Mix