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Presumably most audio tools when regarding volume normalization, find the global maximum volume and normalizes the entire audio file based on that value, to avoid clipping.

It sounds very logical, but is not practical when volume varies in such a way that periods where there is very loud sounds are intercalated with periods of very quiet sounds

For instance in a movie with ocationals explosions, with very quiet scenes in between, where people are whispering most of the time.

So, it would be good to find an out-of-the-box tool that normalizes an audio file dynamicaly calculating the local maximum volume amplitude

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3 Answers

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Have you tried Levelator ? (though i have not used it)

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Well.... That's what I'm talking about...!!! Thanks very much –  rraallvv Nov 23 '12 at 6:05
    
Just notice that Levelator is intended for speech and does not work so well with f.ex. music. –  Ken Fyrstenberg Nov 23 '12 at 11:50
    
Thanks it's good to know it. I've not tested Leveler with music, I guess there could be better tools for that matter. –  rraallvv Nov 24 '12 at 2:21
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In the old days a quick and dirty way to get a little more out of audio would use "maximizing" where you found the max top and then scaled all data to the max value within the available bit range (in those days 8-, 12- and 16-bit - today most are 24-bit or floating point).

However, this approach is linear and doesn't work so well as we hear sound logarithmic. That is, even if we double the amplitude's value we won't hear it as "double volume". For that decibel is used and RMS (root-mean-square).

All movies and commercial music tracks are manually crafted - a process called mastering which gives the final touch to a track and is what makes it sound so good (though you find cheap services that can process your music and claim it will be mastered using automatic settings - not the same).

The main tools to get a proper master is EQ, compressor, limiter and sometimes a bunch of other tools. The mastering engineer will often have his own bag of tools and settings. And a compressor isn't just any compressor (or limiter, EQ etc.). Each has its own flavor and characteristics. But it comes down to the human ear, in particular the one of the engineer. The environment for mastering is very important as well and you will find the top-notch equipment in such studios.

I would like to mention this as this site target more the professional aspect in audio-video productions.

You can get a quick-fix with tools such as Levelator, although, you will never be able to get what you hear in movies or music with it. If you are seeking that kind of sound (movie and music) you will either learn how to master (or even basic mixing techniques can help you to get better sound) or send the audio to a studio that provides mastering. Mastering is considered a separate art/skill in music/audio production and takes a while to learn.

There is however no standard process to work on an audio track. This is because each track is different and require different approaches and settings. This is the main reason why automatic tools of today cannot produce what an engineer can produce.

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Thanks, appreciate it. I understand your concern, as movies, TV shows, podcasts, and most media in general, require very good quality audio. Leveler is acceptable in my case as my sound files do not requiere so much processing. I guess my question could clarify better my requirement, as I mentioned a movie as example. –  rraallvv Nov 23 '12 at 20:50
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We built a software which does exactly that (and more): auphonic.com

It's free, like the levelator, but also performs well on music regions.

Actually audio loudness normalization is also a hot topic ATM, see e.g.: https://auphonic.com/blog/2012/08/02/loudness-measurement-and-normalization-ebu-r128-calm-act/ or https://auphonic.com/blog/2011/07/25/loudness-normalization-and-compression-podcasts-and-speech-audio/

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Thanks, It's perfect for my voice notes. Also very interesting readings. –  rraallvv Nov 24 '12 at 2:27
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