RMS Normalize

[steve]

the Effect drop-down menu doesn't show RMS Normalize or Limiter

Perhaps you're not looking low enough down the list of effects. By default it is below the dividing line.

[pato]

You're right; both of these effects appear below the dividing line. However, they (and most others below that line) appear only on my large external video monitor. When using my 15" laptop monitor only 6 of the 19 below-the-line effects appear, and no View setting or scrolling lets me see the rest of them. The Limiter and RMS Normalize effects are alphabetically below the visible 6. How can I see all installed plug-ins when using the 15" monitor?

[steve]

When using my 15" laptop monitor only 6 of the 19 below-the-line effects appear

On Windows you should be able to scroll down the list.

Also on Windows, when the Effect menu is open, pressing (for example) the "L" key, will jump down to the first effect beginning with "L". Press "L" again to jump down to the next effect beginning with "L" ... (obviously any letter can be used other than "L").

An alternative, is that effects may be grouped according to type. See here for more info: http://manual.audacityteam.org/man/effe ... ences.html

[Edward1]

This plug-in is been a lifesaver for me. With that I can set the RMS value within the allowed limitations anywhere within it on the ACX check plug-in. Just discovered this within the last couple of days after posting on it elsewhere in this forum.

[kozikowski]

And as I posted...

There is a simple process for ACX processing. You don't have to guess at it.

viewtopic.php?p=334950#p334950

Koz

[sertal]

Hi Steve, thanks for this plugin, it is very useful.

I'm trying to figure out how to implement a RMS normalization in a software development project I'm working to, where can I find the reference algorithm you used for this plugin?

[steve]

where can I find the reference algorithm you used for this plugin?

This plug-in cleverly "cheats". It lets Audacity do the heavy lifting of calculating the initial RMS value, then simply amplifies (multiplies the sample values by a constant value) as required.

The basic algorithm for measuring RMS is the square root of (the sum of squares of all sample values, divided by the number of samples).

In Audacity, the algorithm is considerably more complicated because Audacity uses cached values per block-file, which are then combined to give a value per audio clip, which are then combined to give a value for the selection, but the caching of block-file values makes the calculation very fast.

[sertal]

Thanks for your answer, Steve.

This plug-in cleverly "cheats". It lets Audacity do the heavy lifting of calculating the initial RMS value,

I'm fine with that, I already implemented the routine to measure the actual RMS of an audio track in my application.

then simply amplifies (multiplies the sample values by a constant value) as required.

This is the missing part, for me: how to define the "constant value" to use? It is clearly related to the target RMS the user wants to achieve, but how?

[steve]

This is the missing part, for me: how to define the "constant value" to use? It is clearly related to the target RMS the user wants to achieve, but how?

Perhaps a little surprising, but it's pretty much the same as "peak normalization".
Just as amplifying a sound by +3 dB causes the peak level to increase by +3 dB, so it also causes the RMS level to increase by +3 dB.

To convert dB to linear:
10 ^ (dB / 20)

So, for example, if you measure the RMS as -24 and you want the RMS to be -20, then you need to amplify by +4 dB.
So to do that, you would multiply each sample value by 10^(4/20) = 1.584893192

[sertal]

Thanks again Steve!

Perhaps a little surprising, but it's pretty much the same as "peak normalization".
Just as amplifying a sound by +3 dB causes the peak level to increase by +3 dB, so it also causes the RMS level to increase by +3 dB.

Incredibly simple! Sorry, I'm a complete newbie in audio manipulation from the sw development perspective... well, time to coding now, thanks so much!