Petko shared with us his experience with music information retrieval (MIR) acquired at SoundCloud. Similar algorithms are employed at Spotify, Pandora, Shazam and SoundHound. The most basic form of music retrieval extracts musical notes from the audio signal. The digital audio signal itself is a sequence of numbers sampled from electrical voltage representing sound waves. Petko explained that the first step in MIR is to perform segmentation of the signal at even intervals (frames), typically lasting 52 ms each.