Digital audio
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Digital audio describes sound recording and reproduction systems which work by using a digital representation of the audio waveform.
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Technology overview
The most common method of creating digital audio is Pulse-code modulation (PCM). PCM digital audio is typically sampled at 44.1 kHz for CD recordings, or higher for professional audio applications. For comparison, speech signals for telephony are only sampled at 8 kHz. Higher sample rates for professional recording are becoming popular. These include 88.2 kHz, 96 kHz, and 192 kHz.
The amplitude of each sample is a numeric value that is represented by a certain number of bits. The more bits that are used to represent the amplitude, the greater the dynamic range that can be represented, with each bit providing a gain of approximately 6 dB. The dynamic range of 16 bit digital audio is therefore approximately 96 dB, whereas the dynamic range of 24 bit digital audio is 144 dB. 8 bit digital audio has a dynamic range of approximately 48 dB.
The amount of data created by digital audio is quite large. 16 bits per sample at 44.1 kHz creates 705600 bits per second. Thus for a stereo recording, approximately 10 MB will be generated per minute. 24 bit, 96 kHz digital audio has a bit rate of 2304000 bits per second, or around 33 MB per minute for stereo. Due to this, different forms of audio data compression have recently become more popular.
Another method of creating a digital representation of the audio waveform is Direct Stream Digital or DSD. The Super audio compact disc uses this format.
Since digital audio, unlike analog audio, is always accompanied implicitly or explicitly by a sample clock, synchronization is a crucial consideration in digital audio systems. This is usually accomplished by genlocking all the systems in a facility to a single master audio clock. Plesiochronous operation is not advisable, as it tends to result in widespread hard-to-debug problems.
Digital audio technologies
- Digital audio tape (DAT)
- DAB (Digital Audio Broadcasting)
- Compact disc (CD)
- DVD
- Minidisc
- Super audio compact disc
- Digital audio workstation
- and various audio file formats
Digital audio interfaces and interconnects
- AC97 (Audio Codec 1997) interface between Integrated circuits on PC motherboards
- ADAT interface
- AES/EBU interface with XLR connectors
- AES47, Professional AES3 digital audio over Asynchronous Transfer Mode networks
- I2S (Inter-IC sound) interface between Integrated circuits in consumer electronics
- S/PDIF, either over coaxial cable or TOSLINK
See also
- Digital audio workstation (DAW)
- Digital audio editor
- Software synthesizer
- Music sequencer
- Amplifier
- Audio compression
- Digital video
- Digital film
- Musical Instrument Digital Interface (MIDI)
- Nyquist-Shannon sampling theorem
- Category:Digital audio
- Valve sound (tube sound)
- Video game music
- Dither
External links
- Information on the ADAT interface (http://www.dmalham.freeserve.co.uk/adat.html)
- Home audio recording forum (http://www.studioathome.com)