Digital audio

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"Digital music" redirects here. For a kind of modern music composed by digital means, see electronic music.
A sound wave, in red, represented digitally, in blue (after sampling and 4-bit quantization).


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. A digital-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.


Overview of digital audio[edit]





Conversion process[edit]

Analog to Digital to Analog conversion

A digital audio system starts with an ADC that converts an analog signal to a digital signal.[note 1] The ADC runs at a specified sampling rate and converts at a known bit resolution. CD audio, for example, has a sampling rate of 44.1 kHz (44,100 samples per second), and has 16-bit resolution for each stereo channel. Analog signals that have not already been bandlimited must be passed through an anti-aliasing filter before conversion, to prevent the distortion that is caused by audio signals with frequencies higher than the Nyquist frequency, which is half of the system's sampling rate.

A digital audio signal may be stored or transmitted. Digital audio can be stored on a CD, a digital audio player, a hard drive, a USB flash drive, or any other digital data storage device. The digital signal may then be altered through digital signal processing, where it may be filtered or have effects applied. Audio data compression techniques, such as MP3, Advanced Audio Coding, Ogg Vorbis, or FLAC, are commonly employed to reduce the file size. Digital audio can be streamed to other devices.

For playback, digital audio must be converted back to an analog signal with a DAC. DACs run at a specific sampling rate and bit resolution, but may use oversampling, upsampling or downsampling to convert signals that have been encoded with a different sampling rate.

History of digital audio use in commercial recording[edit]

Pulse-code modulation was invented by British scientist Alec Reeves in 1937[2] and was used in telecommunications applications long before its first use in commercial broadcast and recording. Commercial digital recording was pioneered in Japan by NHK and Nippon Columbia, also known as Denon, in the 1960s. The first commercial digital recordings were released in 1971.[3]

The BBC also began to experiment with digital audio in the 1960s. By the early 1970s it had developed a 2-channel recorder, and in 1972 it deployed a digital audio transmission system that linked their broadcast center to their remote transmitters.[3]

The first 16-bit PCM recording in the United States was made by Thomas Stockham at the Santa Fe Opera in 1976, on a Soundstream recorder. An improved version of the Soundstream system was used to produce several classical recordings by Telarc in 1978. The 3M digital multitrack recorder in development at the time was based on BBC technology. The first all-digital album recorded on this machine was Ry Cooder's Bop till You Drop in 1979. British record label Decca began development of its own 2-track digital audio recorders in 1978 and released the first European digital recording in 1979.[3]

Sony digital audio recorder PCM-7030

Popular digital multitrack recorders produced by Sony and Mitsubishi in the early 1980s helped to bring about digital recording's acceptance by the major record companies. The 1982 introduction of the CD popularized digital audio with consumers.[3]

Digital audio technologies[edit]

Digital audio broadcasting
Storage technologies

Digital audio interfaces[edit]

Audio-specific interfaces include:

Naturally, any digital bus (e.g., USB, FireWire, and PCI) can carry digital audio. Also, several interfaces are engineered to carry digital video and audio together, including HDMI and DisplayPort.

In professional architectural or installation applications, many digital audio networking protocols and interfaces exist.

See also[edit]


  1. ^ Some audio signals such as those created by digital synthesis originate entirely in the digital domain, in which case analog to digital conversion does not take place.


  1. ^ Janssens, Jelle; Stijn Vandaele and Tom Vander Beken (2009). "The Music Industry on (the) Line? Surviving Music Piracy in a Digital Era". European Journal of Crime 77 (96). doi:10.1163/157181709X429105. 
  3. ^ a b c d Fine, Thomas (2008). "The Dawn of Commercial Digital Recording". In Barry R. Ashpole. ARSC Journal (Ted P. Sheldon). Retrieved 2010-05-02. 

Further reading[edit]

  • Borwick, John, ed., 1994: Sound Recording Practice (Oxford: Oxford University Press)
  • Bosi, Marina, and Goldberg, Richard E., 2003: Introduction to Digital Audio Coding and Standards (Springer)
  • Ifeachor, Emmanuel C., and Jervis, Barrie W., 2002: Digital Signal Processing: A Practical Approach (Harlow, England: Pearson Education Limited)
  • Watkinson, John, 1994: The Art of Digital Audio (Oxford: Focal Press)

External links[edit]