Audacity: A Free, Cross-Platform Digital Audio Editor

• Audacity: One the best Freewares in the internet for editing audio properties
  
• Audacity: A Free, Cross-Platform Digital Audio Editor, under GNU license
  
• Audacity is free, open source software for recording and editing sounds. It is available for Mac OS X, Microsoft Windows, GNU/Linux, and other operating systems
• It can record, add effects to sounds like echo and noise levels, fade in, fade out, increase/decrease volume, change palyback speed, mix waves, .........
• It can convert MP3 to WAV
  
• License: Free under GNU license
  
• Screenshots from Softpedia
  
• Homepage1
  
• Homepage2