Compressors

[Lomas]

I know how they work and I know the parameters, except for one thing. People say, when describing compressors, that they lower loud parts and raise quiet parts. It's the last part that I don't get. If I put a signal through a compressor with a 2:1 ratio, any part of the signal that exceeds the threshold will be lowered by half.
But how does it raise the low signal, unless I use make up gain? The thing is I thought that make up gain is supposed to be used to compensate for change in volume compared to the uncompressed signal, to not be confused by that change in volume.

Is it really a good idea to compress and then use make up gain to increase volume instead of compressing and then raising the fader on a mixer or sequencer? Or doesn't it matter where it's done in this case?

I understand how, if you lower loud parts and then increase the volume you are in a way raising the quiet part and lowering the loud part. Just checking to see if I missed something else.

[aidan_m]

Compressing lowers the louder bits (then add gain to compensate)
Limiting brings up the quiet bits.

Explained much better here:
http://homerecording.com/bbs/showthread.php?t=74122

[mixsit]

Originally Posted by Lomas

...Is it really a good idea to compress and then use make up gain to increase volume instead of compressing and then raising the fader on a mixer or sequencer? Or doesn't it matter where it's done in this case?

Apparently in some designs make up is part of the built in function -aside from a separate output gain. (or perhaps it is how the relative relationship of threshold point and gain are defined) IIRC 'Valley People might have done it as 'built in'(?)
As a practice matter I wouldn't think it would matter if it was built in or where it was done.

Look at it like this too- Half the time if you're just knocking off some tops' there's not much in the way of gain or preceived volume to be 'fixed', and you just go on to making the moves you will do on the balance fader anyway. When there is a audible loss, the make-up knob is good for doing a/b quality comparisons at equal loudness.

[Lomas]

I guess it's like I thought then.

Isn't limiting the same thing as a compressor only with a ratio of at least 10:1?

[Massive Master]

Compressing lowers the louder bits (then add gain to compensate)
Limiting brings up the quiet bits.

Compression lowers the louder parts - Limiting *LIMITS* the louder parts - It does NOT make the quiet parts louder - It STOPS the louder parts cold. Adding gain makes the quiet parts louder (and the louder parts disappear forever).

[Lomas]

So it isn't true that limiting is the same thing as a compressor but with a ratio of at least 10:1

If it is, then theoretically a limiter can let a signal stay over the threshold, right?

[mixsit]

With high ratios they are comp/limiters, but many compressors have attack times that aren't strictly 'brickwall. So you might be looking at matching the unit to the the source (or job) in application.
For example a vocal comp set 10-1 is 'limiting -ie be set up to work mostly on the peaks and be fast enough for that, but wouldn't do the job of a peak stop or clipper'.

If it is, then theoretically a limiter can let a signal stay over the threshold, right?

I believe so. (Let's call in some help here... Some times it's enough just to do an amount of control that's needed with some amount of overshoot being exceptable.