Microphones are used in many applications such as telephones , tape recorders , hearing aids , motion picture production , live and recorded audio engineering , in radio and television broadcasting and in computers for recording voice . Microphones are used in many applications such as telephones , tape recorders , karaoke systems , hearing aids , motion picture production , live and recorded audio engineering , FRS radios , megaphones , in radio and television broadcasting and in computers for recording voice , speech recognition , VoIP , and for non-acoustic purposes such as ultrasonic checking or knock sensors .