Online mastering studios have been around for a number of years now and many musicians maybe be attracted to the lower prices. There is no doubt that saving some money is on a lot of peoples minds these days. This is understandable, however the online mastering services you can find on the internet are wide and varied along with the pricing that you can find. As an operator of a professional online mastering studio myself I find it quite alarming when looking at the websites of some people offering online mastering services. It is very obvious to a mastering professional what studios seem ill equipped or lacking in experience and skill that mastering requires. As such I thought it would be a good idea to list some of the things to look out for when choosing mastering. Firstly I will clarify what mastering is. Mastering is preparing a body of music works for final release medium. This involves fades, spacing, tonal sonic tweaks, tweaks to the dynamic range of the material, entering sub code data such as ISRC codes and UPC/EAN codes  and quality control. (click, glitch removal etc) A master format might be a CD-R pre master disk or a DDP file or .wav and MP3 files.