Hyee Wang,
The two differ only by a constant term, 2.0E0, otherwise they are
identical...
Rgds,
Andrew
> ITUT G729 preprocessing question
> Posted by: hyeewang@ hyeewang
> Date: Wed Apr 29, 2009 8:36 am ((PDT))
>
> About ITUT G729, I have two questions.
>
> 1. In the processing section of G729 spec, it says to apply a high pass filter
with a cut-off frequency of 140 Hz. As we know, the range of pitch is between 55
and 400 Hz. Then, how to search the pitch with frequency below 140Hz with such a
preprocessing algo? It is as fetching the moon from sea.
>
> 2. G729 preprocessing section uses a second order pole/zero filter with a
cut-off frequency of 140 Hz.
> H(z) =
(0.46363718-0.927247058.*z.^-1+0.46363718*z.^-2)/(1-1.9059465.*z.^-1+0.9114024*z.^-2);
> But ,In contrast to the spec,the G729 codec software implementation uses a
different filter, which is described as follows. It is also 2nd order high pass
filter with cut off frequency at 140 Hz.
>
> To my surpise,I find the frequency response of that filter is bad.
>
> Why? Why the G729 codec software implementation use such a bad
filter,rejecting a designed and perfect filter?
> That puzzle me greatly.
>
> /**
> * 2nd order high pass filter with cut off frequency at 140 Hz. *
> * Designed with SPPACK efi command -40 dB att, 0.25 ri. *
> * *
> * Algorithm: *
> * *
> * y[i] = b[0]*x[i] + b[1]*x[i-1] + b[2]*x[i-2] *
> * + a[1]*y[i-1] + a[2]*y[i-2]; *
> * *
> * b[3] = {0.92727435E+00, -0.18544941E+01, 0.92727435E+00}; *
> * a[3] = {0.10000000E+01, 0.19059465E+01, -0.91140240E+00}; *
> *-----------------------------------*/
>
> Regards
> HyeeWang