How do I use audacity to change the quality of my songs?

I need to do exactly what it says in the following link:



http://www.sciencebuddies.org/science-fa鈥?/a>



I'm using Audacity 1.3 beta, but i can download another version if its easier to explain.How do I use audacity to change the quality of my songs?
To do the comparison test as described in the article you will need the Lame codec.



http://lame.sourceforge.net/



Audacity 1.3 is fine.



Note it is difficult to detect a difference unless doing a direct A-B comparison. That is switching from the original to the compressed track and back again while both are playing.

The quality of the speaker system is also critical.

Unless you're using good quality headphones or are plugged through a good stereo system the exercise will be fruitless.

The lowest compression ratio is 320 kbps. This removes the least amount of audio information from the file and results in the best mp3 quality. 128 kbps is generally accepted as the best compromise between file size and quality.



There is one error in the text which states that 70 minutes is the industry standard for the length of a CD.

This is incorrect.

74 minutes was chosen as this is the playing time of the longest orchestral work.

Until technology caught up blank CDs were only available as 650 Mb / 74 minute. Blank CDs are now available as 700 Mb / 80 minute.

The compact disk was originally developed for the archival storage of data until, as with tape and vinyl, somebody thought "We can use this for music" so compromises had to be reached for bitrate and capacity.

The playing time measured in minutes only applies to files in wav format.How do I use audacity to change the quality of my songs?
get the lame decoder