Hi, Can anyone please explain how decimation using frequency response masking is done?? thanks in advance. Raj.
Decimation filtering using Frequency response masking technique
Started by ●September 25, 2003
Reply by ●September 25, 20032003-09-25
Rajasekaran C wrote:> Hi, > Can anyone please explain how decimation using frequency response > masking is done?? thanks in advance. >=20 > Raj.Raj, I have to guess at your meaning. If you're using a standard term, it refers to something I don't know about. If, by "frequency response masking", you mean what I call filtering, then the answer to your=20 question is simple, even if my explanation is not. When decimating a signal -- reducing its sample rate -- the maximum=20 supportable frequency is also reduces. That part of the original signal=20 that lies above half the new sample rate must be reduced (to avoid aliasing in the decimated signal) before samples are discarded. Those filter outputs that are to be discarded need not be calculated at all unless the workings of a recursive filter needs them. The actual procedure that is best will depend on the degree of decimation, which you didn't' tell us. Jerry --=20 Engineering is the art of making what you want from things you can get. =AF=AF=AF=AF=AF=AF=AF=AF=AF=AF=AF=AF=AF=AF=AF=AF=AF=AF=AF=AF=AF=AF=AF=AF=AF= =AF=AF=AF=AF=AF=AF=AF=AF=AF=AF=AF=AF=AF=AF=AF=AF=AF=AF=AF=AF=AF=AF=AF=AF=AF= =AF=AF=AF=AF=AF=AF=AF=AF=AF=AF=AF=AF=AF=AF=AF=AF=AF=AF=AF=AF=AF
Reply by ●October 2, 20032003-10-02
Hi, Thanks for the reply. What I meant by "frequency response masking" was the removal of the frequency components above the new sample rate by using masking filters. i.e., the unwanted frequencies are masked using filters. I wanted to know whether a decimation filter can be implemented using this technique. Thanks once again for the reply. Regards, Raj. Jerry Avins <jya@ieee.org> wrote in message news:<bkuv53$o9d$1@bob.news.rcn.net>...> Rajasekaran C wrote: > > > Hi, > > Can anyone please explain how decimation using frequency response > > masking is done?? thanks in advance. > > > > Raj. > > Raj, > > I have to guess at your meaning. If you're using a standard term, it > refers to something I don't know about. If, by "frequency response > masking", you mean what I call filtering, then the answer to your > question is simple, even if my explanation is not. > > When decimating a signal -- reducing its sample rate -- the maximum > supportable frequency is also reduces. That part of the original signal > that lies above half the new sample rate must be reduced (to avoid > aliasing in the decimated signal) before samples are discarded. > > Those filter outputs that are to be discarded need not be calculated at > all unless the workings of a recursive filter needs them. The actual > procedure that is best will depend on the degree of decimation, which > you didn't' tell us. > > Jerry
Reply by ●October 2, 20032003-10-02
Rajasekaran C wrote:> Hi, > Thanks for the reply. What I meant by "frequency response masking" > was the removal of the frequency components above the new sample rate > by using masking filters. i.e., the unwanted frequencies are masked > using filters. I wanted to know whether a decimation filter can be > implemented using this technique. Thanks once again for the reply. >=20 > Regards, > Raj.Raj, I guessed your meaning correctly. The process of decimating by an integer ratio 1/N amounts simply to selecting every Nth sample. As you wrote, frequencies that the new sample rate won't support need to be filtered out first. The operations can be combined by using a transversal filter (the usual kind of FIR) and calculating only every Nth output value. A slight embellishment can be used for ratios like M/N. You might want to look at polyphase approach exemplified by http://www.nt.ruhr-uni-bochum.de/lehrstuhl/dsv/publikationen/ecctd99_1.pd= f Jerry --=20 Engineering is the art of making what you want from things you can get. =AF=AF=AF=AF=AF=AF=AF=AF=AF=AF=AF=AF=AF=AF=AF=AF=AF=AF=AF=AF=AF=AF=AF=AF=AF= =AF=AF=AF=AF=AF=AF=AF=AF=AF=AF=AF=AF=AF=AF=AF=AF=AF=AF=AF=AF=AF=AF=AF=AF=AF= =AF=AF=AF=AF=AF=AF=AF=AF=AF=AF=AF=AF=AF=AF=AF=AF=AF=AF=AF=AF=AF
Reply by ●October 2, 20032003-10-02
Hi Raj, I am guessing that you are talking about a technique were you insert zeros inbetween the filter taps to generate a "periodic" filter, then you create another filter "the masking filter" with a lower complexity to get the passband of interest. I've seen this technique used to generate narrowband filters used for decimation. Do a google search on "frequency response masking" and you will find much information on the technique. Jon raaj_cee@msn.com (Rajasekaran C) wrote in message news:<6e6d57f7.0309250151.6cd57523@posting.google.com>...> Hi, > Can anyone please explain how decimation using frequency response > masking is done?? thanks in advance. > > Raj.