Mixing two songs together involves combining both to produce a new single song. This process splits into 4 keys tasks, shown in the following diagram:
(1) - The tempo of both songs must first be extracted accurately.
(2) - The tempo of one or both songs must then be adjusted such that it is identical for both.
(3) - The songs are then aligned relative to one another appropriately, such that beats occur simultaneously.
(4) - Finally the volume of the first song must be turned down whilst the second is turned up - which fades the two songs together in the 'mixing passage'. Once the mix is completed the second song continues to play alone.
The methods used to solve these four tasks are detailed in the Implementation section.
In this project input songs are put into the order in which they will be mixed (see Playlist generation) and the process above is applied repeatedly until all songs have been mixed. (So the composite output of mixing songs 1 and 2 is then mixed with song 3, the output of which is then mixed with song 4, etc...).