Reply by neelufar.2005 May 28, 20072007-05-28
>On May 24, 8:40 am, "neelufar.2005" <neelufar.2...@gmail.com> wrote: >> Hi, >> >> I am a fresher to the DSP field, I am going through the acoustic echo >> cancellation. I want help regarding delay estimation in acoustics echo >> cancellation. Can any one suggest me a good algorithm for this. Help
me
>> for getting good papers on this. Thanks in advance. >> >> Regards, >> Neelufar. >> >> _____________________________________ >> Do you know a company who employs DSP engineers? >> Is it already listed athttp://dsprelated.com/employers.php? > >Actually, you can use the Average Magnitude Difference Function (AMDF) >to estimate delay, and it's computationally cheaper than LMS. > >Maurice Givens
Thanks for your reply sir, I am going through Average Magnitude Difference Function (AMDF), while exploring on this I found a good PDF Enhancing Echo Cancellation via Estimation of delay By Youhong lu,Ronald Fowler,Wenshun Tian and Leland Thompson. In which the delay estimation is done. I am going through this paper to understand the mathematical steps used for estimation of delay. I have got struck with the normalized coss correlation function formule given in this formula. The normalised cross correlation function &#61554;(n,k) at the time n can be defined as R(n,k) = Pxy(n,k) / squareroot[Px(n-k) Py(n)] where x(n) is frend signal and y(n) be recieved echo, where n is the time index. The denominator part I have understood. Px(n) and Py(n) is the power ofx(n) and y(n) I have doubt in this part of the formula. I am not understand how cross correlation is calculated. Pxy(n,k) is the cross correlation function between x(n) and y(n) at ime n. L - 1 Pxy(n,k) = 1/ L summation x*(n- l &#2013266070;k) y(n &#2013266070; l) l = 0 Can you plaese help me in this regard Sir.
> >
_____________________________________ Do you know a company who employs DSP engineers? Is it already listed at http://dsprelated.com/employers.php ?
Reply by Steve Underwood May 24, 20072007-05-24
Vladimir Vassilevsky wrote:
> > Line echo compensation is much simpler than the acoustic echo > compensation. However it is not the task for the beginners either. >
Its not simpler. It just has a rather different set of problems to solve. Steve
Reply by Vladimir Vassilevsky May 24, 20072007-05-24

dbell wrote:

>>>I am a fresher to the DSP field, I am going through the acoustic echo >>>cancellation. I want help regarding delay estimation in acoustics echo >>>cancellation. Can any one suggest me a good algorithm for this. Help me >>>for getting good papers on this. Thanks in advance. >> >> >>Actually, you can use the Average Magnitude Difference Function (AMDF) >>to estimate delay, and it's computationally cheaper than LMS.
Computing the AMDF for all possible lags is not cheaper then the LMS. And the AMDF will be completely destroyed by the delay spread.
> Whether or not there is a definable echo time (delay) depends on what > you mean by acoustic echo. If you mean room reverberation there are > many echoes arriving at different times, one number does not describe > the situation.
For that reason the acoustic echo can be very long. In order to reduce the complexity and improve the convergence, it can be useful to compensate only for the most significant part (or parts) of the echo. The coarse estimation of the delay is required to do that.
> If you mean in a telephone hybrid you may have a > better defined echo time.
Line echo compensation is much simpler than the acoustic echo compensation. However it is not the task for the beginners either. Vladimir Vassilevsky DSP and Mixed Signal Design Consultant http://www.abvolt.com
Reply by dbell May 24, 20072007-05-24
On May 24, 3:55 pm, maury <maury...@core.com> wrote:
> On May 24, 8:40 am, "neelufar.2005" <neelufar.2...@gmail.com> wrote: > > > Hi, > > > I am a fresher to the DSP field, I am going through the acoustic echo > > cancellation. I want help regarding delay estimation in acoustics echo > > cancellation. Can any one suggest me a good algorithm for this. Help me > > for getting good papers on this. Thanks in advance. > > > Regards, > > Neelufar. > > > _____________________________________ > > Do you know a company who employs DSP engineers? > > Is it already listed athttp://dsprelated.com/employers.php? > > Actually, you can use the Average Magnitude Difference Function (AMDF) > to estimate delay, and it's computationally cheaper than LMS. > > Maurice Givens
Whether or not there is a definable echo time (delay) depends on what you mean by acoustic echo. If you mean room reverberation there are many echoes arriving at different times, one number does not describe the situation. If you mean in a telephone hybrid you may have a better defined echo time. Dirk
Reply by maury May 24, 20072007-05-24
On May 24, 8:40 am, "neelufar.2005" <neelufar.2...@gmail.com> wrote:
> Hi, > > I am a fresher to the DSP field, I am going through the acoustic echo > cancellation. I want help regarding delay estimation in acoustics echo > cancellation. Can any one suggest me a good algorithm for this. Help me > for getting good papers on this. Thanks in advance. > > Regards, > Neelufar. > > _____________________________________ > Do you know a company who employs DSP engineers? > Is it already listed athttp://dsprelated.com/employers.php?
Actually, you can use the Average Magnitude Difference Function (AMDF) to estimate delay, and it's computationally cheaper than LMS. Maurice Givens
Reply by Vladimir Vassilevsky May 24, 20072007-05-24

neelufar.2005 wrote:

> I am a fresher to the DSP field, I am going through the acoustic echo > cancellation. I want help regarding delay estimation in acoustics echo > cancellation. Can any one suggest me a good algorithm for this.
Process the old good LMS over the decimated data. That will give you the estimate of the delay in the channel for a moderate computing cost. Vladimir Vassilevsky DSP and Mixed Signal Design Consultant http://www.abvolt.com
Reply by neelufar.2005 May 24, 20072007-05-24
Hi,

I am a fresher to the DSP field, I am going through the acoustic echo
cancellation. I want help regarding delay estimation in acoustics echo
cancellation. Can any one suggest me a good algorithm for this. Help me
for getting good papers on this. Thanks in advance.

Regards,
Neelufar.



_____________________________________
Do you know a company who employs DSP engineers?  
Is it already listed at http://dsprelated.com/employers.php ?