In the perfect case the crossfader would keep constant output level. However, there's no standard how this should be achieved. Many DJ equipment manufacturers offer different mixers for different purposes (e.g. scratching, beatmixing, cut mixing, etc.). High-end mixers often have crossfade curve switches allowing the DJ to select the type of crossfade necessary. Experienced DJs are also able to crossfade between tracks using the channel faders.