
I'm not sure what audio preview is, but if you want to hear a song before you play it, you use the headphone and mixer/controller cue function to do that. For example on my DJM-S11, I would turn the Cue/Master knob over to Cue. Then I would move the cue fader over to channel 1 or 2 depending on which one I've loaded the song up I want to hear, then I keep the crossfader on the side of the playing song, and I listen to the cued song in my headphones and the audience cannot hear it yet. When I want them to hear it I can move the crossfader so both channels are audible or I can move the crossfader all the way to the other side so only the song I was listening to myself a second ago can be hear. I can then repeat the process with the other deck. This is a fundamental part of djing.