Noise normalization: Difference between revisions
(I just noticed a comment there were Monty mentions coding a solution in linear time, that's pretty damn good in terms of O(n) complexity ;-D.) |
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'''Noise normalization''' is special type of coding technique (somewhat comparable [[PNS]] used in [[AAC]], but not the same) used by [[Ogg Vorbis]] psychoacoustics model to '''compensate''' for loss of energy in certain frquency 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''' ''(see [http://trac.xiph.org/cgi-bin/trac.cgi/file/trunk/vorbis/lib/psy.c psy.c] in source, '''_vp_noise_normalize_sort''' function)''. This is main cause of most ''metallic artifacts'' in MP3. It is '''one factor''' that gives Vorbis it's ''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 7. | '''Noise normalization''' is special type of coding technique (somewhat comparable [[PNS]] used in [[AAC]], but not the same) used by [[Ogg Vorbis]] psychoacoustics model to '''compensate''' for loss of energy in certain frquency 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''' ''(see [http://trac.xiph.org/cgi-bin/trac.cgi/file/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 it's ''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 7. | ||
Revision as of 21:24, 9 January 2006
Noise normalization is special type of coding technique (somewhat comparable PNS used in AAC, but not the same) used by Ogg Vorbis psychoacoustics model to compensate for loss of energy in certain frquency 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 (see 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 it's 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 7.