what armin was doing was mixing keys, in part 1 he went from F to F#, in part 1 he went from F# to G he said 8 to 9 beats per minute equal half a note, so a sharp or a flat, so to go up a key he was playing the F# song and sped it up so it was G so it matched the next song he had lined up could also be done the opposite, pitch down your track in G to it becomes F# so it match's when you bring it in