User:Dlevine123/Digital audio

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This article is about the technology used to record sound. For the defunct magazine originally named "Digital Audio", see CD Review.

"Digital music" redirects here. For modern music composed by digital or electronic means, see Computer music and Electronic music. Audio levels display on a digital audio recorder (Zoom H4n)

Digital audio is a representation of sound recorded in, or converted into, digital form. In digital audio, the sound wave of the audio signal is typically encoded as numerical samples in a continuous sequence. For example, in CD audio, samples are taken 44,100 times per second, each with 16-bit sample depth. Digital audio is also the name for the entire technology of sound recording and reproduction using audio signals that have been encoded in digital form. Following significant advances in digital audio technology during the 1970s and 1980s, it gradually replaced analog audio technology in many areas of audio engineering, record production and telecommunications in the 1990s and 2000s. With growing digital circuit technology, digital emulations can now accurately replicate analog hardware .

Typically, In a digital audio system, an analog electrical signal representing the sound is converted with an analog-to-digital converter (ADC) into a digital signal, typically using pulse-code modulation (PCM). This digital signal can then be recorded, edited, modified, and copied using computers, audio playback machines, and other digital tools. When the sound engineer wishes to listen to the recording on headphones or loudspeakers (or when a consumer wishes to listen to a digital sound file), a digital-to-analog converter (DAC) performs the reverse process, converting a digital signal back into an analog signal, which is then sent through an audio power amplifier and ultimately 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. Unlike analog audio, in which making copies of a recording results in generation loss and degradation of signal quality, digital audio allows an infinite number of copies to be made without any degradation of signal quality.

Overview[edit]
A sound wave, in red, represented digitally, in blue (after sampling and 4-bit quantization).

Digital audio technologies are used in the recording, manipulation, mass-production, and distribution of sound, including recordings of songs, instrumental pieces, podcasts, sound effects, and other sounds. Modern online music distribution depends on digital recording and data compression. The availability of music as data files, rather than as physical objects, has significantly reduced the costs of distribution as well as made it easier to share copies. Before digital audio, the music industry distributed and sold music by selling physical copies in the form of records and cassette tapes. With digital-audio and online distribution systems such as iTunes, companies sell digital sound files to consumers, which the consumer receives over the Internet. Popular streaming services such as Spotify and Youtube, offer temporary access to the digital file, and are now the most common form of music consumption. Digital audio files, unlike analog recordings can be shared and copied without loss of quality or resolution.

Technologies[edit]
Sony digital audio tape recorder PCM-7030

Digital audio is used in broadcasting of audio. Standard technologies include Digital audio broadcasting (DAB), Digital Radio Mondiale (DRM), HD Radio and In-band on-channel (IBOC).

Digital audio in recording applications is stored on audio-specific technologies including CD, Digital Audio Tape (DAT), Digital Compact Cassette (DCC) and MiniDisc. Digital audio may be stored in a standard audio file formats and stored on a Hard disk recorder, Blu-ray or DVD-Audio. Files may be played back on smartphones, computers or MP3 player.

'''Digital audio resolution is measured in sample depth. Most digital audio formats use a sample depth of either 16-bit, 24-bit, and 32-bit.Digital audio resolution is measured in sample depth. Most digital audio formats use a sample depth of either 16-bit, 24-bit, and 32-bit.'''

Recording[edit]
Main article: Digital recording

Pulse-Code Modulation (PCM) 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 and their Denon brand, in the 1960s. The first commercial digital recordings were released in 1971.

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.

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.

Popular professional digital multitrack recorders produced by Sony/Studer (DASH) and Mitsubishi (ProDigi) in the early 1980s helped to bring about digital recording's acceptance by the major record companies. Machines for these formats had their own transports built-in as well, using reel-to-reel tape in either 1/4", 1/2", or 1" widths, with the audio data being recorded to the tape using a multi-track stationary tape head. PCM adaptors allowed for stereo digital audio recording on a conventional NTCS or PAL videorecorder.

The 1982 introduction of the CD or 'compact disc' popularized digital audio with consumers.

ADAT became available in the early 1990s, which allowed eight-track 44.1 or 48 kHz recording on S-VHS cassettes, and DTRS performed a similar function with Hi8 tapes.

Formats like ProDigi and DASH were referred to as SDAT (Stationary-head Digital Audio Tape) formats, as opposed to formats like the PCM adaptor-based systems and DAT, which were referred to as RDAT (Rotating-head Digital Audio Tape) formats, due to their helical-scan process of recording, such as a compact disc.

Like the DAT cassette, ProDigi and DASH machines also accommodated the obligatory 44.1 kHz sampling rate, but also 48 kHz on all machines, and eventually a 96 kHz sampling rate. They overcame the problems that made typical analog recorders unable to meet the bandwidth (frequency range) demands of digital recording by a combination of higher tape speeds, narrower head gaps used in combination with metal-formulation tapes, and the spreading of data across multiple parallel tracks.

'''Modern Digital audio workstations and audio interfaces allow as many channels in as manny different sampling rates as the computer can effectively run at a single time. This makes multitrack recording and mixing much easier for large projects which would otherwise be difficult with analog gear.'''

Interfaces[edit]
Digital-audio-specific interfaces include:


 * A2DP via Bluetooth
 * AC'97 (Audio Codec 1997) interface between integrated circuits on PC motherboards
 * ADAT Lightpipe interface
 * AES3 interface with XLR connectors, common in professional audio equipment
 * AES47 - professional AES3-style digital audio over Asynchronous Transfer Mode networks
 * Intel High Definition Audio - modern replacement for AC'97
 * I²S (Inter-IC sound) interface between integrated circuits in consumer electronics
 * MADI (Multichannel Audio Digital Interface)
 * MIDI - low-bandwidth interconnect for carrying instrument data; cannot carry sound but can carry digital sample data in non-realtime
 * S/PDIF - either over coaxial cable or TOSLINK, common in consumer audio equipment and derived from AES3
 * TDIF, TASCAM proprietary format with D-sub cable
 * Focusrite USB Interface

Several interfaces are engineered to carry digital video and audio together, including HDMI and DisplayPort. Some interfaces offer MIDI support as well as XLR and TRS analog ports.

For personal computers, USB and IEEE 1394 have provisions to deliver real-time digital audio. USB interfaces have become increasingly popular among independent audio engineers and producers due to their small size and ease of use. In professional architectural or installation applications, many audio over Ethernet protocols and interfaces exist. In broadcasting, a more general audio over IP network technology is favored. In telephony voice over IP is used as a network interface for digital audio for voice communications.

See also[edit]

 * Digital audio editor
 * Digital Audio Workstation
 * Digital synthesizer
 * Frequency modulation synthesis
 * Sound chip
 * Sound Card
 * Audio interface
 * Quantization
 * Sampling
 * Multitrack Recording