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thedisillusioned



Joined: 01/04/13
Posts: 2
mp3 compression - how to test
      #1040786 - 01/04/13 06:19 PM
Hi all

As part of my final year university degree i have to create a track of test signals to test mp3 compression. I understand how mp3 compression works but am not sure on what sort of test signals i should be putting in

Can anyone suggest to me what sort of test signals are good for testing mp3 compression at different bit rates and why or if you have any links to articles that are useful then that would be great

thanks in advance

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Kwackman



Joined: 07/11/02
Posts: 1386
Loc: Belfast
Re: mp3 compression - how to test new [Re: thedisillusioned]
      #1040789 - 01/04/13 06:35 PM
Suzanne Vega "Tom's Diner".

I'm pretty certain this is what the original MPEG developers used, and why Suzanne Vega is known as the mother of MP3.

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Cubase, guitars.


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sambrox



Joined: 20/12/08
Posts: 231
Loc: Denmark
Re: mp3 compression - how to test new [Re: thedisillusioned]
      #1040801 - 01/04/13 08:06 PM
Read this

Cheers,
Sam

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seedy.dk


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BJG145



Joined: 06/08/05
Posts: 3394
Loc: Norwich UK
Re: mp3 compression - how to test new [Re: thedisillusioned]
      #1040830 - 01/04/13 09:46 PM
Incidentally Sonnox produce an interesting plugin for auditioning MP3 compression in real time. (15-day demo available.)

http://www.sonnoxplugins.com/ws/pub/plugins/support/demos.htm

http://dload.sonnoxplugins.com/pub/plugins/Reviews/Pro-Codec-SOS.pdf < br />


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Hugh RobjohnsAdministrator
SOS Technical Editor


Joined: 25/07/03
Posts: 21729
Loc: Worcestershire
Re: mp3 compression - how to test new [Re: thedisillusioned]
      #1040874 - 02/04/13 10:05 AM
MP3 throws stuff away. So you can evaluate the frequency domain perforamnce by uising a test signal that has everything, and then see what's missing after encoding -- white noise for example -- although you'll need a very accurate spectral analysis averaged over many passes t achieve sufficient definition.

The other thing you can do is a null test with the original and processed signals -- but take care over accurate time alignment (a one sample pulse at the start is a handy way of ensuring accurate time-alignment).

More complex signals will obviously challenge the algorithm a lot harder than simple signals, and voices are more revealing of artefacts than other signals simply because we are so familiar with the sounds that real voices make and can spot artefacts more easily.

H

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Technical Editor, Sound On Sound


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A. AuCr



Joined: 12/02/12
Posts: 144
Loc: NEW England
Re: mp3 compression - how to test new [Re: thedisillusioned]
      #1040975 - 02/04/13 10:42 PM
Null testing the mid and side components separately can be particularly revealing. The stereo image suffers greatly at lower bitrates.


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mjfe2



Joined: 11/10/09
Posts: 599
Loc: Cambridge, UK
Re: mp3 compression - how to test new [Re: thedisillusioned]
      #1041048 - 03/04/13 12:35 PM
This is a great essay if you want some cultural studies to back up your project: Jonathan Sterne, "The mp3 as cultural artifact"


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thedisillusioned



Joined: 01/04/13
Posts: 2
Re: mp3 compression - how to test new [Re: A. AuCr]
      #1041745 - 06/04/13 06:14 PM
How would i go about setting up a Null test on pro tools?

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http://disillusioneddesigns.com/


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Martin WalkerModerator
Watcher Of The Skies


Joined: 28/02/01
Posts: 17479
Loc: Cornwall, UK
Re: mp3 compression - how to test new [Re: thedisillusioned]
      #1042156 - 08/04/13 08:01 PM
Quote thedisillusioned:

How would i go about setting up a Null test on pro tools?




You just set up two tracks - one containing the original audio, and the other containing the MP3 version, tweaked so that both are as close to the same level as you can get them, then invert the polarity of one of them and see what's left after the common parts cancel out


Martin

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YewTreeMagic


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Goddard



Joined: 04/04/12
Posts: 949
Re: mp3 compression - how to test new [Re: thedisillusioned]
      #1042442 - 09/04/13 11:10 PM
Quote thedisillusioned:

How would i go about setting up a Null test on pro tools?




If you just want to hear what is being removed from the input signal by the encoding, the Sonnox Fraunhofer codec plug-in as already mentioned above provides that function ("difference" auditioning) in PT.

Assume you've already consulted Fraunhofer's resources (and perhaps even contacted them for guidance?) but if not that might be helpful.


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