https://wiki.hydrogenaudio.org/api.php?action=feedcontributions&feedformat=atom&user=185.94.193.182 2026-04-28T14:17:04Z User contributions MediaWiki 1.44.2 https://wiki.hydrogenaudio.org/index.php?title=Noise_normalization&diff=27570 2017-11-23T10:54:20Z

<p>185.94.193.182: </p> <hr /> <div>'''Noise normalization''' is a special type of coding technique (somewhat comparable to [[PNS]] used in [[AAC]], but not the same) used by [[Ogg Vorbis]] psychoacoustics model to '''compensate''' for loss of energy in certain frequency bands due to quantization (usually because of a low [[SNR]]). The algorithm uses an apsort function to determine where the energy lost in each frequency band is the greatest and compensates the band with the greatest energy lost by '''reviving the residue''' (noise error) ''(see [https://trac.xiph.org/browser/trunk/vorbis/lib/psy.c psy.c] in source, '''_vp_noise_normalize_sort''' function, line 1050)''. This is main cause of most ''metallic artifacts'' in MP3. It is '''one factor''' that gives Vorbis its '''noise-like''' sound characteristics, when the bitrate is too low to encode without susceptible artifacts. In the reference encoder it's used on all quality values less than 4.<br /> <br /> ==References==<br /> * [http://www.hydrogenaudio.org/forums/index.php?showtopic=20132 Noise Normalization and 'HF boost' problem] - The solution that ultimately lead to AoTuV tunings.<br /> <br /> [[Category:Algorithms]]</div>

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