GODJ has two output jacks, the LINE OUT and PHONES. When DJing, speakers are connected to the LINE OUT jack and a headphone is connected to PHONES jack. Now you can monitor your next music without outputting its sound to the speakers. This is the most significant difference between GO-DJ and DJ apps found in the Apple iTunes Store / Google Play Store.
By clicking each VOLUME knob, you can control the output for the headphone sources from TrA or TrB, or destination to right or left channel. Do you know what happens if you click both VOLUME-A and VOLUME-B at same time?
Answer: It switches to LINE OUT sound immediately
In this mode, you can hear the exact same sound as the LINE OUT by the headphone so that you can confirm how the crossfader or effectors are applied to the LINE OUT.