Music Spectrograph allows you to visualize and reverse engineer sound and music. The Music Spectrograph displays music and sound as it might appear on a live piano-roll or MIDI/Music editor. The scrolling graph is of music pitch frequencies versus time. This form of sound visualization can assist with the transcription of music (but only if you ignore harmonics and overtone frequencies). In addition, you can also slow down the audio play rate to make it even easier to transcribe music, or even freeze music in time, using a built-in custom audio re-synthesis mode.
The HotPaw Musical Piano Roll Spectrograph creates a scrolling 12th-octave MIDI pitch-centered spectrogram, either from microphone input or synchronized with playing a sound or music file. To analyze a song in your iTunes library, hit the "Pick Tune" button and choose a music file. Hit the "Use Mic" button on the Music Control panel to switch back to analyzing live audio.
Note: Now requires macOS 10.12 or later