Mastering can be done two ways: in an analog environment, or a digital environment. While analog is generally considered the best quality method for mastering, many home studios are confined to using digital software for the task because of limited budgets. Popular software programs include the Waves L1+Maximizer and the Bias Peak software package.
Audio mastering can be expensive; be very cautious when using a low-priced per-song mastering service. Always request an equipment list and references. A lot of low-priced services offer simple services that can be done at home using normalizing and compressor plug-ins, and the side-by-side comparison of original material versus the mastered material shows little improvement.