RMS Normalizing

[steve]

There is a new "RMS Normalize" plug-in available that may be useful to people engaged in producing audiobooks.
It is available here: http://forum.audacityteam.org/viewtopic ... 78#p293878

[Gembo85]

Hi Steve- thankyou for this.
Without any fiddling, I'm at an RMS of -31.1 dB and peak amplitude of -6.6453. I need to adjust this to fit the ACX perameters of between -18 and -23 and peak -3.
Can I simply use the RMS normaliser to within the spectrum (say -20) and then hard limit the peaks to - 3?
I suspect its much more complicated than that....?

[Gembo85]

Sorry- forgot to attach a clip for your reference- any help on this would be greatly appreciated...

Hi Steve- thankyou for this.
Without any fiddling, I'm at an RMS of -31.1 dB and peak amplitude of -6.6453. I need to adjust this to fit the ACX perameters of between -18 and -23 and peak -3.
Can I simply use the RMS normaliser to within the spectrum (say -20) and then hard limit the peaks to - 3?
I suspect its much more complicated than that....?

[steve]

Your recording level is a little low. That means that you will need to amplify the recording, and that will raise the noise level as well as the signal.
A good level to aim for in your recording is for a maximum peak level of about -6 dB. That gives you a waveform of about half the height of the track when in the default "Waveform" view.

Have you tried just amplifying/normalizing that audio clip to a peak level of -3 dB (as required by ACX) and measuring the RMS level? Try it. I get an RMS of -21.5 dB, which sits close to the middle of the specified (-18 to -23 dB) range, and there are no massive peaks that stand out as being much higher than the rest. In other words, no compression or limiting required.

firsttrack007.png (10.95 KiB) Viewed 4048 times

[Gembo85]

Cheers for getting back to me Steve, really appreciate it- The actual track is 30 minutes long so I think there's a couple of discrepancies that are altering with the values.
Yup, my first port of call was to amplify to -3db peak and the RMS worked out at 27.4. Here is a screen shot of the full waveform after amplifying to -3db peak. I'm going to need to compress first right? Because there's a couple of odd peaks? Or am I best off Isolating those peaks and reducing their amplification before raising the whole thing? It's been a year since I last did this and I'm rusty I'm afraid!

Chapter1wavafterAmptominus3dbpeak.png (296.41 KiB) Viewed 4044 times

[steve]

Could you post a short sample at about the 12:30 mark. I see there is a big spike there.

Also, when you make a screenshot for the forum, please reduce the size of the Audacity window first so that the image fits better in the forum page - it saves a lot of scrolling for those trying to read your post and view the image.

[Gembo85]

Thanks Steve- this is the spike with the amplify to -3b.

[steve]

Taking a somewhat 'unscientific' approach, I've roughly drawn by eye a line showing a kind of "average peak level" of your recording as a whole.

envelope.png (143.89 KiB) Viewed 4038 times

I notice that there's a period of a few minutes where the peaks get higher and higher, then lower again until it finally settles down at about 15:00 back to a similar level as the first 10 minutes. I'm not able to tell from the images 'why' that is - perhaps you were becoming enthralled in the drama, which is a good thing from a 'performance' point of view, but not so good from a recording point of view.

Before you do anything, ensure that you have a good backup copy in WAV format, preferably "32-bit float WAV".

I'd suggest that you try a bit of compression to even out that rise in volume.
It's difficult to judge the settings from just a short sample, but as a starting point I'd suggest something like this:

fullwindow-Compressor-000.png (37.7 KiB) Viewed 4038 times

I'd advise not going much above 4:1 for the compression ratio, and keep the attack time at a couple of seconds or more. The control to twiddle with is the "Threshold".
You will need to normalize to -3 dB after using the compressor.

[Zetrick]

I know this topic is quite old, but I was wondering if there is a way to use this RMS-Normalize function in a chain? I'd would like to batch process multiple files with it, and having to open each file and run it can take a long time...

Thanks!

[steve]

I know this topic is quite old, but I was wondering if there is a way to use this RMS-Normalize function in a chain?

Yes, once the plug-in has been installed it can be used in a Chain.