Digital audio

Digital audio describes sound recording and reproduction systems which work by using a digital representation of the audio waveform.

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 48 kHz (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 certian number of bits. The more bits that are used to represent the amplitude, the greater the dynamic range that can be represented. The dynamic range of 16 bit digital audio is aproximatly 96 dB, whereas the dynamic range of 24 bit digital audio is 144 dB. 8 bit digital audio has a dynamic range of approximatly 48 dB.

The amount of data created by digital audio is quite large. 16 bit 44.1kHz creates 705600 bits per second. Thus for a stereo recording, there will 10MB per minute. 24 bit, 96kHz digital audio has a bit rate of 2304000 bits per second, or 33MB per minute for stereo

Another method of creating a digital representaion of the audio wavefrom 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 isn't advisable, as it tends to result in widespread hard-to-debug problems.

Digital audio technologies:

• Digital audio tape (DAT)
• Compact disc (CD)
• DVD
• Minidisc
• Super audio compact disc
• and various audio file formats

Digital audio interconnects:

• AES/EBU interface with XLR connectors
• S/PDIF, either over coaxial cable or TOSLINK
• ADAT interface

See also:

• Audio compression
• Software synthesizers
• Digital video
• Digital film
• MIDI
• Nyquist-Shannon sampling theorem

External links

• Information on the ADAT interface (http://www.dmalham.freeserve.co.uk/adat.html)

Common misspelling and questions (FAQ)

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