# Compression : Peak & RMS

Discussion in 'Mixing & Song Critique' started by paradice, Aug 7, 2008.

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• AT5047

The New AT5047 Premier Studio Microphone Purity Transformed

1. Hi all..
can someone briefly explain the difference between peak and rms compression and its applications

thank you

2. The explains it well.

Drums signals are going to have a higher peak level than an RMS equivalent pad or bowed string.

Also because RMS level is a root mean square average over time, the peak level detection will have a faster attack at the cost of some distortion.

Joined:
Mar 31, 2007
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North Vancouver
Ah yep
RMS is the Root mean square,

To simplify things you can think of the rms level as a average level. Say you have 3 bank accounts. Each bank account has 3 different amounts of money.

Say:
Bank 1 = \$40
Bank 2 = \$50
Bank 3 = \$60

The average amount of money per bank would be:

(40 + 50 + 60) / The number of Banks (3) = 150/3 = 50

Now the rms value is a bit different calculation:

The rms average amount of money per bank would be:

((40^2 + 50^2 + 60^2) /3)^(1/2) = ((1600 + 2500 + 3600)/3)^(1/2) =2567^(1/2)

=50.7

Peak is the largest value. Either negative or positive. In electronics you will hear the term peak to peak. Think of a sine wave swinging around 0V. The distance from the OV mark to the crest, be it negative or positive is the peak value.
Check this link for pretty pictures:

http://ourworld.compuserve.com/homepages/g_knott/elect39.htm

In Simple Math ->
You can convert overall peak values to overall rms just multiply by 0.707 =(1 /root 2).

So.... in peak mode your compressor looks for peaks to act on. usefull for catching quick transients, tameing a ACU GTR for example. Peak compression when used with a large ratio and slow release times will be more noticeable. In this mode the RMS filter in the control path is removed.

In rms mode the compressor responds to changes in the rms level.
The overall level will be smoothed out. In this mode the rms filter in the control path is engaged, and the control signal (either the input (feedforward) or output (feedback)) is changed into an rms level. This dc level then controls the amout of attenuation in the gain control device (Typically a VCA or optical device).

Hope this helps.

• AT5047

The New AT5047 Premier Studio Microphone Purity Transformed