Spreading function slopes 
Spreading function slopes 
Aug 21 2004, 07:23
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#1


MPEG4 AAC developer Group: Developer Posts: 398 Joined: 1June 03 Member No.: 6943 
About a year or 2 ago, there was a posting by someone by the name of Yan..
It was a very interesting issue.. which is to switch the slope of the spreading function so that the lower slope is less steeper than the upper slope.. Initially, I thought I found something interesting when I tried calculating the r_normalization factors and compared to the R_norm of the MP3 ISO specs.. I now think that Yan is wrong.. and MP3 ISO specs is wrong about the r_normal.. Both slopes should be identical in steepness.. Yan's proposal would result in audible artifacts.. Not only that.. refering to the orginal SNR equation : SNR = (14.5 + i) * tb +(1tb)* 5.5 this is when the spreading function slope is steeper in the upper slope than in the lower slope.. just as in Layer II and Layer I psychoacoustic model II.. when it was changed to SNR = 29 *tb + (1tb)*6.0 in MP3, both slope of the spreading function has to be modified to make them identical in steepness to compensate for the constant TMN.. Try working out the mathematical equations.. wkwai 


LoFi Version  Time is now: 26th January 2015  08:54 