One important aspect of mastering audio

One mystery of mastering audio that often goes overlooked is figuring out sound quality in other playing devices. Even professionals will tell you that when mastering audio, sometimes the sound quality is much different in other devices. One trick is to test your audio mastering samples on five different set of speakers such as: a cell phone, a computer, a TV, a car, and standard audio monitors. This test should give you some assurance that your mastering levels are up to standards.