The mastering engineer is responsible for a final edit of a product and preparation for manufacturing copies. Although there are no official requirements to work as an audio mastering engineer, practitioners often have comprehensive domain knowledge of audio engineering, and in many cases, may hold an audio or acoustic engineering degree. Most audio engineers master music or speech audio material. The best mastering engineers might possess arrangement and record production skills, allowing them to 'trouble-shoot' mix issues and improve the final sound. Generally, good mastering skills are based on experience, resulting from many years of practice.