Normalization - under the hood

Effects, Recipes, Interfacing with other software, etc.

If you require help using Audacity, please post on the forum board relevant to your operating system:
Windows
Mac OS X
GNU/Linux and Unix-like

Normalization - under the hood

Permanent link to this post Posted by jim1001 » Sun Mar 18, 2018 6:17 pm

Can anyone tell me what Audacity uses under the hood for its normalization effect?

I've used Normalize in Audacity with the default options:
Remove DC offset
Normalize max amplitude to -1.0 dB

and it does what I want.

However I'd like to use ffmpeg so I can apply to audio in a video.

I've been trying ffmpeg-normalize but not sure how to get same results as Audacity.

Grateful for any help. Thank you.
jim1001
 
Posts: 6
Joined: Sun Mar 18, 2018 5:56 pm
Operating System: Windows 7

Re: Normalization - under the hood

Permanent link to this post Posted by kozikowski » Sun Mar 18, 2018 6:23 pm

Normalize and Amplify are sisters. They turn the volume of the whole performance up or down to meet the criteria. Full stop.

If you Normalize to -1dB for example, you should be able to find at least one place in the performance where one peak in the blue sound waves reached -1db. This can be a little rough to see since the waves are in percent, but the bouncing sound meters should show it.

You can also change the sound waves to dB, but that can be even harder to see.

If you actually want processing and mastering, that's a whole different set of tools.

Koz
kozikowski
Forum Staff
 
Posts: 39870
Joined: Thu Aug 02, 2007 5:57 pm
Location: Los Angeles
Operating System: OS X 10.9 Mavericks

Re: Normalization - under the hood

Permanent link to this post Posted by kozikowski » Sun Mar 18, 2018 11:59 pm

I did the sums for you.

-1dB works out to be 89.1% which you can convert (.891) and round off to 0.9 in Audacity-speak.

You can grab the bottom of the timeline and pull down to make it taller and it will actually show you that. Then all you need to do is find the one peak (up or down) which lives at -1dB.

Screen Shot 2018-03-18 at 16.53.07.png
Screen Shot 2018-03-18 at 16.53.07.png (12.39 KiB) Viewed 143 times


I have this conversion table. I ran one of the numbers backwards and they seem to work. Click the graphic to see the whole thing.

This is the perfect illustration of why you never ordinarily do sound in percent. The sound channel, for example in an Audio CD goes to -96dB. Look at where the percent would be if you did that.

Percent-dB_Conversion .png
Percent-dB_Conversion .png (11.48 KiB) Viewed 143 times


Koz
kozikowski
Forum Staff
 
Posts: 39870
Joined: Thu Aug 02, 2007 5:57 pm
Location: Los Angeles
Operating System: OS X 10.9 Mavericks

Re: Normalization - under the hood

Permanent link to this post Posted by jim1001 » Mon Mar 19, 2018 10:44 am

Thanks for your time & help.

In this case I was really trying to find out if Audacity is using ffmpeg behind the scenes to do the normalization & what ffmpeg options would be needed to get same results as Audacity. I've been trying ffmpeg-normalize. I know this is a question about ffmpeg *and* Audacity but there isn't a common forum as far as I know ;)

All the best,
Jim
jim1001
 
Posts: 6
Joined: Sun Mar 18, 2018 5:56 pm
Operating System: Windows 7

Re: Normalization - under the hood

Permanent link to this post Posted by steve » Mon Mar 19, 2018 11:10 am

jim1001 wrote: was really trying to find out if Audacity is using ffmpeg behind the scenes to do the normalization

No it doesn't.

FFmpeg is purely optional for Audacity and used to extend the range of audio formats that can be imported / exported.

The Normalize effect is one of the standard built-in effects. It makes use of Audacity's "summary data" (a unique feature of Audacity projects) to determine the peak amplitude of the selected audio, (which is very fast and efficient), and then multiplies each selected sample by an appropriate amount to scale the waveform to the desired level.
9/10 questions are answered in the FREQUENTLY ASKED QUESTIONS (FAQ)
steve
Site Admin
 
Posts: 46815
Joined: Sat Dec 01, 2007 11:43 am
Operating System: Linux *buntu

Re: Normalization - under the hood

Permanent link to this post Posted by jim1001 » Mon Mar 19, 2018 11:29 am

OK Steve, many thanks for the explanation. Knowing that, I'll try & figure out what options will do similar in ffmpeg / ffmpeg-normalize.

All the best,
Jim
jim1001
 
Posts: 6
Joined: Sun Mar 18, 2018 5:56 pm
Operating System: Windows 7


Return to Audio Processing



Who is online

Users browsing this forum: No registered users and 3 guests