Mm - hmm.
Well , if you compare the first figure to this one  Actually the scale is not the same , but if you look at the  the numbers um  you clearly see that the difference between the C - zero of the speech and C - zero of the noise portion is larger. Uh but what happens is that after spectral subtraction ,  you also increase the variance of this  of C - zero.
Mm - hmm.
And so if you apply variance normalization on this , it completely sc screw everything. Well.