Digital audio is technology that can be used to record, store, generate, manipulate, and reproducesound using audio signals encoded in digital form. Following significant advances in digital audio technology during the 1970s, it rapidly replaced analog audio technology in most areas of sound production, sound engineering and telecommunications. A microphone converts sound to an analog electrical signal, then an analog-to-digital converter(ADC)—typically using pulse-code modulation—converts the analog signal into a digital signal. Adigital-to-analog converter performs the reverse process, converting a digital signal back into an analog signal, which analog circuits amplify and send to a loudspeaker. Digital audio systems may include compression, storage, processing and transmission components. Conversion to a digital format allows convenient manipulation, storage, transmission and retrieval of an audio signal. In media production and publishing, content is information and experiences that provides value for an end-user or audience. Content is "something that is to be expressed through some medium, as speech, writing or any of various arts."Content can be delivered via many different media including the internet, television, and audio CDs, books, magazines, live events, such as conferences and stage performances. An audio signal is a representation of sound, typically as an electrical voltage. Audio signals have frequencies in the audio frequency range of roughly 20 to 20,000 Hz (the limits of human hearing). Audio signals may be synthesized directly, or may originate at a transducer such as a microphone, musical instrument pickup, phonograph cartridge, or tape head. Loudspeakers or headphones convert an electrical audio signal into sound. Digital representations of audio signals exist in a variety of formats.