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Compression: Rms vs Peak
Old 27th February 2008
  #1
Gear interested
 

Thread Starter
Compression: Rms vs Peak

Hi everyone,

I've been researching all over the internet to find out as much as I can about the two different modes of compression. I've so far understand all the definitions, technically speaking the behaviours, and all the calculations of RMS. But I still dont quite get the difference in the outcomes; so RMS deals with the average signal of the input and doesn't handles the peaks? What if the input signal only has so few peaks above the threshold, then it is better off using the Peak mode?

What I'm looking for is more of a visual explanation of the how an original input signal would differ by using either the Peak or RMS mode.

if anyone can help me out? THANK YOU!
Old 27th February 2008
  #2
Lives for gear
 

The usual reason for choosing the RMS method of detection is "leveling". Please understand that often when using compression , you let peaks get through!
Inside the compressor when the detection circuit looks at the envelope ( there is always a lag between when the over threshold situation is detected and when the turn it down thing happens ! It may be in thousands of a secound , but it happens , that's why digital limiting has look-ahead so as to not let things slip through ; but thats a different subject).

So since you asked about RMS detection, keep in mind that the detector now has to calculate what the average loudness (RMS ) is before it decides about wheter that value is over threshold. So it's a little slower at this . You set your threshold around the place where the RMS is "modulating" ( These are all averaged values so it does'nt have anything to do with those spikes you see in a waveform) ; thus "leveling".

There are RMS mode compressors that have lookahead, but this will only help to not let burst (not instantaineous peaks!) of loudness ( a :mini-chunk ) get through. This is also realted to attack settings , where as you , once again , are not trying to stomp down peaks , so the attack settings can be set slower , but lookahead in this context ( rms leveling) lets you set attack slower ( for a natural sound ) but still catch "peaks" (mini burst of average loudness , not peaks. ( this stuff happens in milliseconds so remember were just trying to "visuallize whats happening).

Some people like to put 2 compressors in a row , with the first one in a more instantaineous , peak catching set-up and then the "leveling" rms compressor, or , vice versa!!

While your studying, look into "Crest Factor" and remember , that this is one of those subjects that you almost always have to keep after as there are so many different ways to approach and put "Dynamics processing" into practice!

Read the "compression uncompressed tuitorial hereIndependent Recording Network

it's good




Good Luck!!



heh
Old 28th February 2008
  #3
Gear interested
 

Thread Starter
THX! Now I got it! I was thinking also that the perfect compression would be using both modes one after another.

thank you very much!

So what kind of compressors can I find the look-ahead function in???
Old 28th February 2008
  #4
Mastering
 

I've added about 3 pages worth of discussion on RMS versus Peak style compressors in the second edition of my book.

Here's a tip:

If the snare drum stands out too far and you want to zero in on that with less effect on the vocal, then likely you need more peak sensitivity than RMS. However, with either style of compressor, if the attack knob is versatile enough, you can "mimic" or vary your style to taste.

For de-essing, peak compression is tops. For basic leveling RMS compression usually wins out. And there are compressors with a continuous control to vary its style between RMS and peak.

BK


Quote:
Originally Posted by oblivio View Post
Hi everyone,

I've been researching all over the internet to find out as much as I can about the two different modes of compression. I've so far understand all the definitions, technically speaking the behaviours, and all the calculations of RMS. But I still dont quite get the difference in the outcomes; so RMS deals with the average signal of the input and doesn't handles the peaks? What if the input signal only has so few peaks above the threshold, then it is better off using the Peak mode?

What I'm looking for is more of a visual explanation of the how an original input signal would differ by using either the Peak or RMS mode.

if anyone can help me out? THANK YOU!
Old 28th February 2008
  #5
Lives for gear
 

Quote:
Originally Posted by oblivio View Post
So what kind of compressors can I find the look-ahead function in???

There are many ; Wavearts track plugg comes to mind. Also , if your host can deal with a 4 input mode VST , the check out REAcomp here REAPER | ReaPlugs The Price is right (free!) this plugg has look-ahead ( they call it pre-comp I believe , and you can adjust the window size for the RMS averaging( it's a fader that , if I'm not mistaken , is like the continuous control that Bob described in his post .)



Cheers
Old 28th October 2014
  #6
Gear interested
 

I've found that rms compression gives you a much louder product, upon comparing some of my earlier tracks to those of my favorite artists, I discovered that they had a much louder RMS value than mine, thus I experimented and found that rms is, in my opinion, much better than peak for leveling, I would definitely recommend the peak setting for sidechaining and if you wanted something to add a little more glue to your peaks in the final mix a bit of peak compression on the master bus doesn't hurt too much, but definitely don't overdo it. Hope this helps at least a little bit!

Cheers!
Old 29th October 2014
  #7
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Hermetech Mastering's Avatar
 

Verified Member
How does one know if their compressor is peak or RMS sensing? Just wondering about my Chandler Germ comps!

Oh, and nice thread necromancy BTW!
Old 29th October 2014
  #8
Registered User
 

Quote:
Originally Posted by Hermetech Mastering View Post
How does one know if their compressor is peak or RMS sensing? Just wondering about my Chandler Germ comps!

Oh, and nice thread necromancy BTW!
Should be in the settings/preferences. Even Audacity's in-the-box compressor contains a checkbox - "Compress based on peaks". Also, check the specifications in the (online)manual.
Old 29th October 2014
  #9
Quote:
Originally Posted by The_K_Man View Post
Should be in the settings/preferences. Even Audacity's in-the-box compressor contains a checkbox - "Compress based on peaks". Also, check the specifications in the (online)manual.
Classic!
Old 29th October 2014
  #10
Lives for gear
 
Hermetech Mastering's Avatar
 

Verified Member
Quote:
Originally Posted by Broyhillio View Post
Classic!
Indeed...



I'll shoot Wade an email and ask.
Old 30th October 2014
  #11
Lives for gear
 
Retinal's Avatar
Quote:
Originally Posted by Hermetech Mastering View Post
Indeed...



I'll shoot Wade an email and ask.
Now I'm jealus of you germ comps plugins..
wait wut?
Old 30th October 2014
  #12
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Hermetech Mastering's Avatar
 

Verified Member
Heard back from Wade, they are peak sensing!
Old 23rd September 2016
  #13
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jasonallenh's Avatar
Quote:
Originally Posted by bob katz View Post
and there are compressors with a continuous control to vary its style between rms and peak.

Bk
urei 7110!!!!!!!!!!!!!
Old 23rd September 2016
  #14
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Laurend's Avatar
 

Peak signal value is relevent for limiting.
RMS value is a pseudo RMS according a time window. A 50 ms window can measure the signal down to 20 Hz. Larger windows are OK for leveling. Compressors need pseudo RMS.
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