HOWTO: amplify mp3 file without clipping

I tried to make my own iphone ringtones.
But the music I choose has very small volume, so I need it to be louder.
Google gave me the solution.

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ref : http://forum.audacityteam.org/viewtopic.php?f=28&t=14567&sid=cf371db3400fa65f5c5575b8c5b3fc13

Chris's page -> audacity plug-in : http://pdf23ds.net/software/dynamic-compressor/

install Chris's dynamic compressor plug-in :
1. download "compress.ny" file from chris's page.
2. copy it to /usr/share/audacity/plug-ins/ (ubuntu jaunty 9.04)
3. restart audacity

Audacity -> select all range ->

1. menu > effect > amplify > set dB to (given dB) - 0.1 to prevent clipping
2. menu > effect > plug-ins > compress dynamics
3. change parameters, and click ok.