[Vorbis] several questions

[fangchao]

VorbisHi
Any help is appreciate.
I have two questions.
First, I looked into the vorbis-Ⅰ-specific and was confused by the floor1 algorithm.
I think at last the aim is to derive the piecewise curve with the list X and Y,then when encodering ,why not
use the selected point orderly to get the curve ?   In other words, the specific use the list of [0,128,64,32,96,16,48,80] ,
why can not use [0,16,32,48,64,80,96,112,128] and encoder the diffence between the Y and the previous Y  directly? 
Second, from the previos letter,I know that floor is the least squared error approximation of the maximum amount of 
noise allowable for each mdct coefficient/frequency (determined by the psychoacustic model). Now I am just confused 
whatever the floor really is .Is it a predition to the MDCT coefficient or just an estimation to the maximum allowable noise?
And how the psychoaustic result is applied to the compution of the floor?

Looking forward to your letter!
 				

　　　　　　　　Lisa
　　　　　　　　fangchao_dlut at sina.com
　　　　　　　　　　2005-09-26