Lossy or Lossless ?-  A quick guide to check your bootlegs
By Alexx1977

When a wave file is encoded into mp3, the higher frequencies are cut to achieve a file size up to ~1/10th of the size of the original. This smaller file size results in less time downloading.
I made two graphs using the Frequency Analysis Tool of Cool Edit Pro 2. If you see a sudden cut at about 15-16 kHz, and the graph goes down to zero and never gets up again, than it's 100% MP3 sourced.

 

This graph shows that our source file is mp3 sourced.

This graph shows that our source is uncompressed audio :