Audio Interchange File Format

2013-06-26T03:09:55Z

94.193.39.224: Spelling.

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'''Audio Interchange File Format''' ('''AIFF''') is an audio [[Container Formats|container format]] developed by Apple Computer for their Macintosh computers.

It is, in a sense, the Mac-world equivalent of the Microsoft [[WAV]] format.

It can hold both uncompressed ([[PCM]]) and compressed data. The compressed formats most commonly found inside AIFF are [[ADPCM]] and [[MACE]].

It supports multichannel streams, high sampling rates and high bit depths. The amount of audio data it holds is limited to 2Gb.

== Additional Reading ==
* [http://www.borg.com/~jglatt/tech/aiff.htm Documentation on the AIFF file format]

[[Category:Container Formats]]

Masking

2013-06-26T03:02:02Z

94.193.39.224: So many spelling errors.

'''Masking''' is based on masking properties of the human ear. In contrast: When you look at the sun and if a bird passes ahead, you do not see it because of the too predominant light of the sun. In audio, it is similar. In the presence of strong sounds, you do not hear the weakest ones. Take for example traffic on a highway. During rush hour construction drilling may limit your ability to a hear an ambulance behind you; henceforth the ambulance is masked or vice versa . Different types of psychoacoustic masking exist and are exploited in most coding systems.

==Masking properties==

* [[TMN]] ''tone masking noise''
* [[NMT]] ''noise masking tone''
* [[TMT]] ''tone masking tone''

==Simultaneous masking==
''Simultaneous masking'' is a [[frequency domain]] phenomenon, where a low-level signal (noise) commonly referred to as the ''maskee'' can be made inaudible by the presence of a stronger signal ''masker'', ''(i.e high amplitude pure tone masking a noise)''. Several of the masking properties listed above are deployed in most coding systems (psychoacoustic models, etc). The masking threshold for each varies depending upon a number of characteristics, which are limited to the SPL and frequency of the masker. In practice high frequency noises are more easily masked.

==Temporal masking==
''Temporal masking'' is a [[time domain]] phenomena by which masking can be exploited before and after a signal, hence [[pre-masking]] and [[post-masking]]. The onset of pre-masking is relatively short and doesn't last upwards of 20 msec. In contrast to that of post-masking, which can last upwards of 50-200 msec after the signal that is being masked, usually the Simultaneous masker.

[[image:Masking.gif|none|frame|Simultaneous masker and the corresponding Temporal masking]]

==References==

* [http://www.hsu-hh.de/ant/index.php?brick_id=WGuDNLyFCEaTWamW&action=setlanguage&language=en# Masking Effects] this applet demonstrates the effects of masking in perceptual coding.
* [http://www.umiacs.umd.edu/~desin/Speech1/node9.html Human Auditory Masking] differences between auditory perception in masking.

[[Category:Psychoacoustics]]

Hydrogenaudio Knowledgebase - User contributions [en]

Audio Interchange File Format

Masking