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
ITUT G729 preprocessing question
Started by ●April 29, 2009
Reply by ●April 29, 20092009-04-29
HyeeWang wrote:> 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.Fundamental frequency is not required to find the pitch.> 2. G729 preprocessing section uses a second order pole/zero filter > with a cut-off frequency of 140 Hz. > 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?Don't know where did you get that junk implementation. Refer to the original ITU-T annex. Anyway the main purpose of this filter is removing DC from the signal, so the frequency response is not critical. Vladimir Vassilevsky DSP and Mixed Signal Design Consultant http://www.abvolt.com
Reply by ●April 29, 20092009-04-29
On Apr 30, 8:02�am, Vladimir Vassilevsky <antispam_bo...@hotmail.com> wrote:> HyeeWang wrote: > > 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. > > Fundamental frequency is not required to find the pitch. > > > 2. G729 preprocessing �section uses a second order pole/zero filter > > with a cut-off frequency of 140 Hz. > > 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? > > Don't know where did you get that junk implementation. Refer to the > original ITU-T annex. Anyway the main purpose of this filter is removing > DC from the signal, so the frequency response is not critical. > > Vladimir Vassilevsky > DSP and Mixed Signal Design Consultanthttp://www.abvolt.comVladimir Vassilevsky ! Thank you. The two filter actually is almost same,except for a scaling of factor 2. Due to my not thinking over the coefficients of that filter,I misplot its frequency response. I just use the vector a[3] of the comments as the parameter of freqz function,forgetting to add the minus sign with the second and third elements. But another question still make me puzzled. Maybe I am confused with the concept of pitch and fundmental frequency. But I did not find the difference of them. So after cutting off the frequency below 140hz of speech,I think it have lost pitch components thus pitch searching algo does not work. Would you be kind to explain it to me? Regards HyeeWang
Reply by ●April 29, 20092009-04-29
HyeeWang wrote:> Maybe I am confused with the concept of pitch and fundmental > frequency. But I did not find the difference of them. So after cutting > off the frequency below 140hz of speech,I think it have lost pitch > components thus pitch searching algo does not work. > Would you be kind to explain it to me?Pitch is a repetition rate. If a signal is repeated with the frequency Fo, that doesn't mean that there are any components at the frequency Fo. Vladimir Vassilevsky DSP and Mixed Signal Design Consultant http://www.abvolt.com
Reply by ●April 30, 20092009-04-30
On 30 Apr., 03:18, HyeeWang <hyeew...@gmail.com> wrote:> Would you be kind to explain it to me?You better get text books about it. This way you (a) won't waste people's time and (b) you'll learn something. Second option: Quit your job and get a new one that doesn't require competency in DSP. btw: I'm the one who told you about the equivalence of the two filters (up to a scaling factor) in another forum. Funny, how you sometimes try to look smart by repeating other people's responses and making it look like it was the result of your thoughts. Cheers! SG
Reply by ●April 30, 20092009-04-30
On Apr 30, 12:34�pm, SG <s.gesem...@gmail.com> wrote:> On 30 Apr., 03:18, HyeeWang <hyeew...@gmail.com> wrote: > > > Would you be kind to explain it to me? > > You better get text books about it. This way you (a) won't waste > people's time and (b) you'll learn something. > Second option: Quit your job and get a new one that doesn't require > competency in DSP. > > btw: I'm the one who told you about the equivalence of the two filters > (up to a scaling factor) in another forum. Funny, how you sometimes > try to look smart by repeating other people's responses and making it > look like it was the result of your thoughts. > > Cheers! > SGhi,SG. Thank you. It looks as like you are argry that I "repeating other people's responses and making it look like it was the result of your thoughts. " The two filter actually is almost same,except for a scaling of factor 2. It is a basic fact. I did not think over and forget the minus signs and mistake the response. Thank you for you reminding me to that. But I have expressed thinkful to you in that forum. More ,it is in another forum. How can you wanna me to do here? Could you teach me? Regards HyeeWang
Reply by ●April 30, 20092009-04-30
On Apr 30, 1:08�pm, HyeeWang <hyeew...@gmail.com> wrote:> On Apr 30, 12:34�pm, SG <s.gesem...@gmail.com> wrote: > > > > > > > On 30 Apr., 03:18, HyeeWang <hyeew...@gmail.com> wrote: > > > > Would you be kind to explain it to me? > > > You better get text books about it. This way you (a) won't waste > > people's time and (b) you'll learn something. > > Second option: Quit your job and get a new one that doesn't require > > competency in DSP. > > > btw: I'm the one who told you about the equivalence of the two filters > > (up to a scaling factor) in another forum. Funny, how you sometimes > > try to look smart by repeating other people's responses and making it > > look like it was the result of your thoughts. > > > Cheers! > > SG > > hi,SG. > Thank you. > > It looks as like you are argry that I �"repeating other people's > responses and making it > look like it was the result of your thoughts. " > > The two filter actually is almost same,except for a scaling of factor > 2. > > It is a basic fact. I did not think over and forget the minus signs > and mistake the response. > Thank you for you reminding me to that. > > But I have expressed thinkful to you in that forum. More ,it is in > another forum. How can you wanna > me to do here? > Could you teach me? > > Regards > HyeeWang- Hide quoted text - > > - Show quoted text -Thank all teachers in my long journey. Maybe I should tell that it is *** who teach me every knowledge ,including 1+1=2,here. hehe. Regards HyeeWang
Reply by ●April 30, 20092009-04-30
> > >HyeeWang wrote: > >> 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. > >Fundamental frequency is not required to find the pitch. > >> 2. G729 preprocessing section uses a second order pole/zero filter >> with a cut-off frequency of 140 Hz. >> 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? > >Don't know where did you get that junk implementation. Refer to the >original ITU-T annex. Anyway the main purpose of this filter is removing>DC from the signal, so the frequency response is not critical.Its more than just an issue of removing DC. You need to remove the entire bass end of the spectrum to optimise the performance of the codec. This is true of most narrowband speech codecs. Even with an elementary codec like G.711, filtering below something like 200Hz dramatically improves how well the remainder of the signal codes. Steve
Reply by ●April 30, 20092009-04-30
"steveu" <steveu@coppice.org> wrote in message news:N_-dnV-RhPr12mTUnZ2dnUVZ_tidnZ2d@giganews.com...> > > > > >HyeeWang wrote: > > > >> 1. In the processing section of G729 spec, it says to apply a high > >> pass filter with a cut-off frequency of 140 Hz.> > Anyway the main purpose of this filter is removing > >DC from the signal, so the frequency response is not critical. > > Its more than just an issue of removing DC. You need to remove the entire > bass end of the spectrum to optimise the performance of the codec. This is > true of most narrowband speech codecs. Even with an elementary codec like > G.711, filtering below something like 200Hz dramatically improves how well > the remainder of the signal codes.I agree. There could be a lot of energy at low frequencies, however that part is not very important for the perception of the speech. It only wastes the bandwidth. Same idea applies to the power amplification. What always surprised me in the G.711, G.721 and such: why didn't they use a fixed preemphasis/deemphasis in the analog. It improves the quality very noticeably. Vladimir Vassilevsky DSP and Mixed Signal Consultant www.abvolt.com
Reply by ●May 4, 20092009-05-04
steveu,thank you. 1. Removing DC is reasonable,for it is not a part of speech at all.But what is the reason to remove bass? How and why it can optimise the performance ? We should be to noted that G729 is not a waveform coder,not a frequency domain waveform coder also, it is a parameter vocoder. 2. G711, as an elementary coder algo, use the basic A/mu law nonuniform PCM quantization. I wonder whether it can be called "codec". How it can be dramatically improves the quality? Vladimir Vassilevsky. Thank you. G.711, G.721, two elementary coding algo, use basic A/mu law nonuniform PCM quantization and ADPCM. They all use waveform to compress data. It is nothing about frequency domain. Why you wanna use a fixed preemphasis/deemphasis in them? How u expect it work? Any comments would be appreciated. HyeeWang@gmail.com
