How Shazam works Sep 22 2010
The Shazam algorithm fingerprints a song by generating this 3d graph, and identifying frequencies of "peak intensity." For each of these peak points it keeps track of the frequency and the amount of time from the beginning of the track. Shazam builds their fingerprint catalog out as a hash table, where the key is the frequency. When Shazam receives a fingerprint like the one above, it uses the first key (in this case 823.44), and it searches for all matching songs.