Timecode

Special vinyl records (or CDs/digital files played with CDJs) can be used with DJ software to play digital music files with DJ software as if they were pressed onto vinyl, allowing turntablism techniques to be used with digital files. These vinyl records do not have music recordings pressed on to them. Instead, they are pressed with a special signal, referred to as "timecode", to control DJ software. The DJ software interprets changes in the playback speed, direction, and position of the timecode signal and manipulates the digital files it is playing in the same way that the turntable manipulates the timecode record.
This requires a specialized DJ sound card with at least 4 channels (2 stereo pairs) of inputs and outputs. With this setup, the DJ software typically outputs unmixed signals from the music files to an external hardware DJ mixer. Some DJ mixers have integrated USB sound cards that allow DJ software to connect directly to the mixer without requiring a separate sound card.