You are here

mp3 compression - how to test

For everything after the recording stage: hardware/software and how you use it.

mp3 compression - how to test

Postby thedisillusioned » Mon Apr 01, 2013 6:19 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
thedisillusioned
Posts: 2
Joined: Sun Mar 31, 2013 11:00 pm

Re: mp3 compression - how to test

Postby Kwackman » Mon Apr 01, 2013 6:35 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.
User avatar
Kwackman
Frequent Poster
Posts: 784
Joined: Thu Nov 07, 2002 12:00 am
Location: Belfast

Cubase, guitars.


Re: mp3 compression - how to test

Postby sambrox » Mon Apr 01, 2013 8:06 pm

Read this

Cheers,
Sam
User avatar
sambrox
Regular
Posts: 232
Joined: Sat Dec 20, 2008 12:00 am

Re: mp3 compression - how to test

Postby BJG145 » Mon Apr 01, 2013 9:46 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
User avatar
BJG145
Frequent Poster
Posts: 2988
Joined: Fri Aug 05, 2005 11:00 pm
Location: Norwich UK

 


Re: mp3 compression - how to test

Postby Hugh Robjohns » Tue Apr 02, 2013 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
User avatar
Hugh Robjohns
Moderator
Posts: 17098
Joined: Thu Jul 24, 2003 11:00 pm
Location: Worcestershire, UK

Technical Editor, Sound On Sound


Re: mp3 compression - how to test

Postby A. AuCr » Tue Apr 02, 2013 10:42 pm

Null testing the mid and side components separately can be particularly revealing. The stereo image suffers greatly at lower bitrates.
A. AuCr
Regular
Posts: 154
Joined: Sun Feb 12, 2012 12:00 am
Location: NEW England

Re: mp3 compression - how to test

Postby mjfe2 » Wed Apr 03, 2013 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"
User avatar
mjfe2
Frequent Poster
Posts: 558
Joined: Sat Oct 10, 2009 11:00 pm
Location: London, UK

Re: mp3 compression - how to test

Postby thedisillusioned » Sat Apr 06, 2013 6:14 pm

How would i go about setting up a Null test on pro tools?
thedisillusioned
Posts: 2
Joined: Sun Mar 31, 2013 11:00 pm

Re: mp3 compression - how to test

Postby Martin Walker » Mon Apr 08, 2013 8:01 pm

thedisillusioned wrote: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
User avatar
Martin Walker
Moderator
Posts: 9844
Joined: Wed Jan 13, 2010 8:44 am
Location: Cornwall, UK

Steampunk & Synth News | Mad Scientist Mode


Re: mp3 compression - how to test

Postby Goddard » Tue Apr 09, 2013 11:10 pm

thedisillusioned wrote: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.
User avatar
Goddard
Frequent Poster
Posts: 997
Joined: Tue Apr 03, 2012 11:00 pm

 



Who is online

Users browsing this forum: No registered users and 2 guests