Digital audio is the name for digitized audio signals (music etc.).

Transformation analog-digital

Similar audio signals consist of (air) waves. Digitization means to transform these infinitely exact waves lossy into numeric values. In addition the values of the audio signals must sufficiently often be scanned and stored. According to in digital signal processing scanning theroem must the sampling rate admitted more be than twice as large like the highest frequency of the signal which can be scanned. One scans too rarely, then the so-called alias Effekt.Da most humans only signals to zirka 20kHz develops to hear, audio signals for CDs with 44,1kHz is scanned. Higher frequencies in the audio signal must be filtered before (similar), since one hears here otherwise a humming (the aliasing became the too high frequencies on low frequencies "“down-throws"”).

DVDs and DAT work with 48kHz, newer formats and professional music productions even up to 192kHz.

High scanning rates increase not only the possible maximum frequency, but facilitate also both similar and digital treatment of the audio material: if the SAM polarizing rate the available is higher than the necessary, then digital audio effects of more Samples can consult for the computation and thus e.g. interpolate speed aspect ratio better. More to it under over scanning.

Since during the digital analog transformation a reflected signal develops above the maximum utilizable frequency, this must be removed with similar filters (Hicut/low-pass). Ideal way with 44,1kHz SAM polarizing rate below 22,05kHz all portions would loss-free be passed (low-pass), above 22,05kHz be however completely suppressed. Since such steilflankigen filters are to be manufactured complex, one can use the range from 22,05kHz to 24kHz than sliding range with a higher scanning rate (for example 48kHz) for the low-pass and use thus with similar Frequenzumfang more inexpensive Hicuts.

More importantly than the scanning rate is the volume range, which is described with PCM by the SAM polarizing width. It indicates, how many volume gradations can be coded digitally. While one cannot notice an increase of the SAM polarizing rate of 48kHz on 96kHz only with difficulty or, an extension the SAM polarizing width of 16 on 24Bit for the ear is clearly audible.

Coding

For unkomprimierte PCM-coded audio data large data sets result. The necessary storage location per second results out:

• Byte per second = SAM polarizing rate * SAM polarizing width * channels

For CD (44,1kHz, 16bit, 2 channels) thus 176400 bytes per second or 10,1MB per minute result.

For the reduction of these data sets formats were created such as Ogg/Vorbis or MP3, which reach a struggle of the data sets by lossy treatment. Depending upon desired output quantity the quality does not vary thereby between noticeably and strongly verfremdet; one speaks of compression artifacts: if it is audible, the selected resulting bit rate is to be differentiated too small and the result thereby clearly from the original to.

Music exchange stock exchanges

The emergence and private use of the Internets made a spreading possible of digital audio files in before ungekanntem extent. Exchange stock exchanges such as Napster contained hundredthousands music-file-frequently are it only source for no more by disk companies not offered clay/tone carriers.

Playing devices

Audio Player make a playing of compressed audio files at the computer in addition, portable Player possible are since some years with constantly growing memory and function range on the market. Frequently these devices control however only MP3 or WMA. Since WMA is patent afflicted a data format and MP3, the manufacturing firms can limit the use of the Audiodatein by a change of the license politics, prevent or with additional costs to provide. For WMA it is for a long time pay by play in the discussion with which each individual playing of the Songs is only rented liable to pay the costs or music. Better devices use therefore the patent-free Ogg/Vorbis format, for which royalties can be never raised, since it is publicly accessible for everyone.

See also: DVD, CD, mp3, digitization

Related links

• http://www.vorbis.com
• http://www.iis.fraunhofer.de/amm/techinf/layer3/
• Audio after MIDI change: What means recognition of Conversion programs audio after MIDI and general information, theses, mathematics and physics for the toner identification

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