The first thing anyone learns about the MP3 audio format is that it is based on a lossy compression algorithm. Lossy compression means that in order to reduce the file size some of the original audio has been removed which inherently reduces the fidelity of the recording. How much data is removed during the compression process is a based on a combination of factors including user preference, portability requirements, available disk space, etc. In the case of an MP3 download the user little control over how much fidelity has been removed from the audio source.

In very simple terms the difference in fidelity can be demonstrated by removing letters from certain words in the following sentence. This is w_at a sentence wo_ld lo_k like if it was compres_ed usi_g a_ imaginary los_y compres_ion algorithm. It doesn