Audacity is a Free sound editing software developed by the open source community, and can be downloaded at http://audacity.sourceforge.net. It is free, but its packed with so many features that  one can’t help but thank the open source community for such a product. For the features it offers, the utilities are endless. Let me show you one example of how this software can be put to use.

To convert a sound track into a ringtone for your mobile phone, here is what you would do.

Import the audio track into Audacity.

Select the portion of the audio track that you want as your ringtone. Copy it. Create a new instance (File->New) and Paste the selected sound clip into the new empty workspace (Edit->Paste)

  

 

Apply the desired effects (there is a lot you can do here). 

For e.g. select the portion of the track towards the end, and apply the fade-out effect (this ensures that the sound track fades out, and doesn’t end abruptly).
 

 

And finally, export the sound clip as an MP3. Apply the desired options (for e.g. setting the bitrate etc.) and thats it! 

 

Of course, if you are looking for a professional sound editing software, with all the bells and whistles, you could try Adobe SoundBooth, Avid, Goldwave or some other commercial alternative.