Digital audio
From The Art and Popular Culture Encyclopedia
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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 and telecommunications in the 1990s and 2000s.
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.
Interfaces
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
Several interfaces are engineered to carry digital video and audio together, including HDMI and DisplayPort.
For personal computers, USB and IEEE 1394 have provisions to deliver real-time digital audio. 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