Some amateur (and a few professional) engineers are self-taught, and learn mostly by doing, or with the help of an instruction manual. Many engineers started in other studio jobs (such as running errands), and learned about recording as they became familiar with the studio where they worked. An engineer learns about the use and placement of microphones, how to operate and maintain an audio mixer, recording deck, sound effects, and other machines, and how to switch between live and recorded sounds, to make the best, and often the most unique, recording possible. A good engineer will strive to make recordings that are both of high technical quality, and also pleasing to hear.