It is impossible to convert a mp3 to MIDI. Mp3s are actual copies (compressed lossy) of actual sound waves. Real sound. MIDI contains no sound at all. All it contains is a text file that has: what BPM, what note is being played, how hard the note is played, how long the note is played, and what instrument is being played. No actual audio is contained. A midi file can sound very different depending on what play back device is playing it. This is do to every midi device containing different samples.