Noise music is a category of music that is characterised by the expressive use of noise within a musical context. This type of music tends to challenge the distinction that is made in conventional musical practices between musical and non-musical sound. Noise music includes a wide range of musical styles and sound-based creative practices that feature noise as a primary aspect. It can feature acoustically or electronically generated noise, and both traditional and unconventional musical instruments. It may incorporate live machine sounds, non-musical vocal techniques, physically manipulated audio media, processed sound recordings, field recording, computer-generated noise, stochastic process, and other randomly produced electronic signals such as distortion, feedback, static, hiss and hum. There may also be emphasis on high volume levels and lengthy, continuous pieces. More generally noise music may contain aspects such as improvisation, extended technique, cacophony and indeterminacy, and in many instances conventional use of melody, harmony, rhythm and pulse is dispensed with.