R/E/P Community

Please login or register.

Login with username, password and session length
Advanced search  

Pages: 1 [2] 3 4 ... 10   Go Down

Author Topic: One thing I don't understand about compressors  (Read 22086 times)

zmix

  • Hero Member
  • *****
  • Offline Offline
  • Posts: 2828
Re: One thing I don't understand about compressors
« Reply #15 on: April 10, 2006, 01:05:29 am »

brett wrote on Sun, 09 April 2006 17:14

Compression is upward ...

No... Compression operates around a rotation point. If the threshold is set to -10dB and the ratio is 2:1 then a signal entering the compressor at 0dB will exit at -5dB and a signal entering the compressor at -20dB will leave at -15dB.

A limiter will not affect the level until the threshold is exceded. In the same scenario, a signal entering a limiter at -20dB will leave at -20dB (plus whatever makeup gain), but the dynamic range is LINEAR until the threshold is crossed.

-CZ

brett

  • Hero Member
  • *****
  • Offline Offline
  • Posts: 1114
Re: One thing I don't understand about compressors
« Reply #16 on: April 10, 2006, 03:09:56 am »

zmix wrote on Mon, 10 April 2006 06:05

brett wrote on Sun, 09 April 2006 17:14

Compression is upward ...

No... Compression operates around a rotation point. If the threshold is set to -10dB and the ratio is 2:1 then a signal entering the compressor at 0dB will exit at -5dB and a signal entering the compressor at -20dB will leave at -15dB.

A limiter will not affect the level until the threshold is exceded. In the same scenario, a signal entering a limiter at -20dB will leave at -20dB (plus whatever makeup gain), but the dynamic range is LINEAR until the threshold is crossed.

-CZ


At unity gain, compression is upward meaning the quieter sections are brought up decreasing dynamics. While expansion is downward in that the quieter sections are brought downward to create dynamics.  
Logged

dcollins

  • Hero Member
  • *****
  • Offline Offline
  • Posts: 2815
Re: One thing I don't understand about compressors
« Reply #17 on: April 10, 2006, 05:13:44 am »

brett wrote on Mon, 10 April 2006 00:09


At unity gain, compression is upward meaning the quieter sections are brought up decreasing dynamics. While expansion is downward in that the quieter sections are brought downward to create dynamics.  


Hello?

It's from the top down.

Is this what you mean?

http://recforums.prosoundweb.com/index.php/m/51317/831/?srch =remedial#msg_51317

DC

compasspnt

  • Hero Member
  • *****
  • Offline Offline
  • Posts: 16266
Re: One thing I don't understand about compressors
« Reply #18 on: April 10, 2006, 09:50:49 am »

brett wrote on Sun, 09 April 2006 17:14


A compounder does both compression and expansion and usually gating and limiting used on individual tracks like vocals and bass.  


I find that these devices usually "compound" the problem.
Logged

zmix

  • Hero Member
  • *****
  • Offline Offline
  • Posts: 2828
Re: One thing I don't understand about compressors
« Reply #19 on: April 10, 2006, 12:14:09 pm »

brett wrote on Mon, 10 April 2006 03:09


At unity gain, compression is upward meaning the quieter sections are brought up decreasing dynamics. While expansion is downward in that the quieter sections are brought downward to create dynamics.  

"Unity gain" has nothing to do with the action of a compressor, but only refers to the gain setting of a device at which Vi=Vo.

If a compressor is 'bringing up quieter sections' and the makeup gain is adjusted so that those sections exit the compressor at the same level that they went in (aka 'Unity Gain') you will find that the overall level has been reduced.

Are people getting all this nonsense from Bob Katz book?

WTF?


I guess I might agree with BK about the horrors of compression: The compression required to fit a 30000 word explanation into a single chapter is HIGHLY destructive...


-CZ

esteso

  • Newbie
  • *
  • Offline Offline
  • Posts: 20
Re: One thing I don't understand about compressors
« Reply #20 on: April 12, 2006, 05:22:33 am »

Ok, still confused. Can I just make it really simple here so that I can understand it? In the thread DC posted a link to earlier BK says, "...... compressors increase gain on the release"

Why? Increase gain relative to what?

If we assume a hard knee, .1ms release compressor, we return to unity gain immediately when gain drops below threshold, yes?

Logged
Michael Telle
Vagabond
Bay Area

tom eaton

  • Hero Member
  • *****
  • Offline Offline
  • Posts: 3640
Re: One thing I don't understand about compressors
« Reply #21 on: April 12, 2006, 04:34:54 pm »

compressors increase gain on the release... think double negative.  compressors decrease gain reduction as the compressor releases.

z-mix... can you explain this:

"If the threshold is set to -10dB and the ratio is 2:1 then a signal entering the compressor at 0dB will exit at -5dB and a signal entering the compressor at -20dB will leave at -15dB."

where does the 5dB gain increase come from on the -20dB signal?  this equation would say that a signal entering your compressor at -50dB will leave it at -30.

if you've applied 5dB of makeup gain, your 0dB signal would exit at 0dB, not -5.

to the best of my knowledge a compressor is a gain REDUCTION device, no?

-t

Ronny

  • Hero Member
  • *****
  • Offline Offline
  • Posts: 2739
Re: One thing I don't understand about compressors
« Reply #22 on: April 12, 2006, 08:32:04 pm »

compasspnt wrote on Mon, 10 April 2006 09:50

brett wrote on Sun, 09 April 2006 17:14


A compounder does both compression and expansion and usually gating and limiting used on individual tracks like vocals and bass.  


I find that these devices usually "compound" the problem.




Can you "expand" on that statement, or are we just "limited" to the "compressed" text version?
Logged
------Ronny Morris - Digitak Mastering------
---------http://digitakmastering.com---------
----------Powered By Experience-------------
-------------Driven To Perfection---------------

Ged Leitch

  • Hero Member
  • *****
  • Offline Offline
  • Posts: 1057
Re: One thing I don't understand about compressors
« Reply #23 on: April 12, 2006, 08:39:30 pm »

i think we've hit a "brickwall" with this topic and see no need to go on anymore as my boredom "threshold" has dropped to -130dbfs and need to "make up" my loss of interest by "exapnding" my mind with some "high ratio" thought process.......ahem...
Logged
http://bitheadmastering.co.uk/

"...But I don't wanna be a pirate!"

Ronny

  • Hero Member
  • *****
  • Offline Offline
  • Posts: 2739
Re: One thing I don't understand about compressors
« Reply #24 on: April 12, 2006, 09:04:13 pm »

TER wrote on Wed, 12 April 2006 16:34

compressors increase gain on the release... think double negative.  compressors decrease gain reduction as the compressor releases.

z-mix... can you explain this:

"If the threshold is set to -10dB and the ratio is 2:1 then a signal entering the compressor at 0dB will exit at -5dB and a signal entering the compressor at -20dB will leave at -15dB."

where does the 5dB gain increase come from on the -20dB signal?  this equation would say that a signal entering your compressor at -50dB will leave it at -30.

if you've applied 5dB of makeup gain, your 0dB signal would exit at 0dB, not -5.

to the best of my knowledge a compressor is a gain REDUCTION device, no?

-t




Not correct on the second paragraph, threshold does not change ratio. Knee does somewhat. If you input the comp at -20dB with a 2:1 ratio, your gain reduction would be -10dB. If your ratio is 5:1 and threshold is -10dB your signal is reduced in gain by -2dB. Ratio is fixed and threshold only determines the level where the compressor comes on and starts reducing gain.

Knee determines how gradual or sharp the leveling slope is when the compressor reaches threshold level. A soft knee cuts the compressor on gradually and a hard knee cuts the compressor on faster. In this way full ratio is not reached immediately with a soft knee, but eventually will reach full ratio, whereas a very hard knee will reach the ratio immediately.

On the last point, a compressor is a gain reduction device, yes. By lowering gain above the threshold, more headroom can be applied, output level can be increased, RMS goes up, so when you make up gain, perceived loudness goes up and louder than the input signal. It is technically a gain reduction device that is used to increase gain on output. By keeping transients down, constant gain can be turned up louder, thus more impact and what a compressor is commonly used for. Bringing lower sounds up while keeping the sharper louder transients down. A brickwall limiter is typically a compressor set to infinity ratio and knee very hard.

Compressors don't exactly increase gain on release, they simply pass the same input signal when the signal falls below the threshold level, so a better way to look at it, is that the signal is restored to unity when the compression is released, not increasing gain when released. IOW, when the signal is below the threshold level, the input and output are at unity gain, no effective ratio, no effective knee, nothing but the input signal untouched by the compressor and only increased in gain from the signal when it was compressed, not from input, so no real increase in the signal when the compression is released.
Logged
------Ronny Morris - Digitak Mastering------
---------http://digitakmastering.com---------
----------Powered By Experience-------------
-------------Driven To Perfection---------------

tom eaton

  • Hero Member
  • *****
  • Offline Offline
  • Posts: 3640
Re: One thing I don't understand about compressors
« Reply #25 on: April 12, 2006, 10:03:31 pm »

Ronny-- read the statement by Z-mix carefully. It's copied from the bottom of the first page in this topic.  Z-mix stated that an input BELOW threshold would INCREASE in level. That's the point that I am questioning.

The first line of my post is in response to the post just above it where someone didn't understand Katz's explanation, in which Bob said "compressors increase gain during release."


-t

Ronny

  • Hero Member
  • *****
  • Offline Offline
  • Posts: 2739
Re: One thing I don't understand about compressors
« Reply #26 on: April 12, 2006, 10:24:09 pm »

TER wrote on Wed, 12 April 2006 22:03

Ronny-- read the statement by Z-mix carefully. It's copied from the bottom of the first page in this topic.  Z-mix stated that an input BELOW threshold would INCREASE in level. That's the point that I am questioning.

The first line of my post is in response to the post just above it where someone didn't understand Katz's explanation, in which Bob said "compressors increase gain during release."


-t



I'm arguing against zmix's point. Again, compressors only increase gain on release from the compression. Once the signal falls below the threshold, the signal does not increase beyond what it was at input, in the first place. To say that a compressor increases gain when the signal is below threshold IS NOT CORRECT. zmix wasn't reading Bob's statement correctly. It's true that when a compresor releases, gain increases, HOWEVER, If the signal never reaches threshold level, it is still below threshold the compressor never comes on and the signal remains neither lowered or increased in gain.

The correct statement would be, when the signal "FALLS" below threshold "AFTER BEING COMPRESSED" gain is increased. NOT when a signal is "BELOW" threshold gain is increased. Understand what I'm saying? The compressor never comes on when signal is below threshold and passes "unity" gain. The more logical statement in my opinion, would be "when a signal is below the threshold level, no gain reduction is applied".  
Logged
------Ronny Morris - Digitak Mastering------
---------http://digitakmastering.com---------
----------Powered By Experience-------------
-------------Driven To Perfection---------------

tom eaton

  • Hero Member
  • *****
  • Offline Offline
  • Posts: 3640
Re: One thing I don't understand about compressors
« Reply #27 on: April 12, 2006, 11:12:35 pm »

I get it.. as should have been clear from my earlier posts!  I think the "increasing gain" thing is honestly less confusing as a double negative, which is to say:  "the compressor decreases gain reduction during release from compression."

Bob's statement could have been much more clear. Z-mix's example is just wrong and I was trying to (gently) make the point.

-t

zmix

  • Hero Member
  • *****
  • Offline Offline
  • Posts: 2828
Re: One thing I don't understand about compressors
« Reply #28 on: April 13, 2006, 03:12:24 am »

Ronny wrote on Wed, 12 April 2006 22:24


I'm arguing against zmix's point. Again, compressors only increase gain on release from the compression.



This is not true. A compressor operates on a rotation point and a limiter operates above threshold.


A little reading of Michael Morgan's research (analog Devices application note AN 135) will clear this up. Here is an excerpt:

index.php/fa/2669/0/

zmix

  • Hero Member
  • *****
  • Offline Offline
  • Posts: 2828
Re: One thing I don't understand about compressors
« Reply #29 on: April 13, 2006, 03:14:23 am »

index.php/fa/2670/0/
Pages: 1 [2] 3 4 ... 10   Go Up