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Dynamic range compression with command line version
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Author:  elrombe [ Tue Jun 17, 2008 4:22 pm ]
Post subject:  Dynamic range compression with command line version
Hello all,

I was wondering if it possible, and if so, how, to change the dymamic range of a wav file (or mp3). I need the dynamic range not to exceed the value of 7db.
Any help/comment will be appreciated.

Thank you very much
Elrom Behar
Author:  hvz [ Tue Jun 17, 2008 7:10 pm ]
Post subject:  Re: Dynamic range compression with command line version
Because the input signal can drop to 0, the output signal can also drop to 0. So a dynamic range of 7 dB is impossible to guarantee...

What are you trying to achieve?
Author:  elrombe [ Wed Jun 18, 2008 8:41 am ]
Post subject:  Re: Dynamic range compression with command line version
Hey,
First, 10x for the reply.
The problem is that:
We have to produce a video clip to be used on TV. One of requirments we have to achive is that the dynamic range of the audio in the clip will not be greater then 7db, as I indicated before.
The way that we produce the audio is by playing a bunch of mp3 which are captured to a wav file. This wav file is then added to the video and encoded to an mpg file.
The output audio dynamic range that we get is larger than the limit allowed. We are looking for a way to meet this requirment. If you have another solution, such as limiting the recording level or something else we will be happy to hear about it.
Author:  hvz [ Wed Jun 18, 2008 12:49 pm ]
Post subject:  Re: Dynamic range compression with command line version
How do you measure the dynamic range?

From Wikipedia: "The dynamic range is defined as the difference between the minimum and maximum amplitude a given device can record."

So, if the maximum is 0 dB (maximum peak level is usually defined as 0), then you should NEVER get below -7. But that's not possible - you can always have a moment of silence (unless you add a lot of noise - silence on a CD is -96 dB, and making silence louder still gives silence).

So my guess would be that the required dynamic range here must be something else, maybe something like "95% of the signal must stay within the 7 dB range". Or: "within every second, the volume should reach the 0..-7 dB region".

How do you currently measure the dynamic range?
Author:  elrombe [ Thu Jun 19, 2008 9:38 am ]
Post subject:  Re: Dynamic range compression with command line version
We used a sofware called RightMark Audio Analyzer 6.1.0.
The requiremnt is "Dynamic Audio Range : no greater than 7dB"
(http://www.google.com/adwords/tvads/tvguidelines.html)
A feedback that we recieved indicated as follows :

Failed audio requirements: The dynamic audio range is approximately
14dB. Operator applied a 2.0 audio compression.

I must note that the feedback was on an mpg file while we checked the wav that later used to create the mpg file.
We were wondering how we can get the dynamic range value and fix it autmatically.
Author:  hvz [ Fri Jun 20, 2008 12:49 am ]
Post subject:  Re: Dynamic range compression with command line version
I just couldn't believe the 7 dB requirement, and I've Googled a bit on Google adwords :-)

This is what I found:
Quote:
What is the dynamic audio range?

The dynamic audio range is the difference between the peak and average audio level in your spot. This ratio should not exceed 7dB. Basically, the difference between the peak audio level and average audio level cannot be too large.
So Google's definition does not correspond to what I though and what Wikipedia describes. Also, it is definitely NOT what RightMark measures - RightMark measures the difference between the loudest and SOFTEST part instead of average.

Hint: Open the generated .WAV file in a wave file editor. Or look at the output sliders of Stereo Tool. If the peak level is not more than 7 dB louder than the average level, you're ok.

Hint: To trick Google to broadcast your ad louder, use the Loudness filter... :-)
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