Calculate FFT in blocks and then average it.
in [DSP]
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From: robert bristow-johnson on 10 Aug 2010 16:31 On Aug 10, 3:54 pm, Jerry Avins <j...(a)ieee.org> wrote: > On 8/10/2010 2:58 PM, Ron N. wrote: > > > On Aug 10, 5:57 am, Jerry Avins<j...(a)ieee.org> wrote: > >> 3) Since all relative phase information is lost by creating the blocks, > >> compute the magnitudes of the bins. > > > If you know the block offsets, then relative phase information > > isn't lost. This allows options such as coherent averaging > > for narrower bin-centered filtering, or interpolation of more > > bins or frequencies between blocks using phase vocoder > > methods. > > Do you suppose that anyone who asked the original question could manage > to do that? well, Ron's right (and i missed it too). you have to add (or subtract) a linear phase term (same as rotating the complex value) with slope proportional to the known block offset. i think then you have to do the averaging to the complex values of each bin. r b-j
From: Jerry Avins on 10 Aug 2010 18:34
On 8/10/2010 4:31 PM, robert bristow-johnson wrote: > On Aug 10, 3:54 pm, Jerry Avins<j...(a)ieee.org> wrote: >> On 8/10/2010 2:58 PM, Ron N. wrote: >> >>> On Aug 10, 5:57 am, Jerry Avins<j...(a)ieee.org> wrote: >>>> 3) Since all relative phase information is lost by creating the blocks, >>>> compute the magnitudes of the bins. >> >>> If you know the block offsets, then relative phase information >>> isn't lost. This allows options such as coherent averaging >>> for narrower bin-centered filtering, or interpolation of more >>> bins or frequencies between blocks using phase vocoder >>> methods. >> >> Do you suppose that anyone who asked the original question could manage >> to do that? > > well, Ron's right (and i missed it too). you have to add (or > subtract) a linear phase term (same as rotating the complex value) > with slope proportional to the known block offset. i think then you > have to do the averaging to the complex values of each bin. Not have to, but can. Of course Ron is right. Just remember: the OP asked, among other things, how to divide his "vector" into equal-sized "blocks". Do you imagine that he could have phase aligned the transformed blocks without more instruction than he could follow? I've been helping bewbies for a long time. I must have written about my second-grade classmate who began to whimper during the lunch period, but it's worth repeating here. Going home for lunch had been permitted when we were in first grade. The rule changed when we got to second grade and everyone had to bring lunch to school, even my classmate who lived across the street. (It was a local side street, but his mother didn't allow him to cross it alone.) About the second week of school, the guy began to whimper quietly while we we still in the gym where we gathered to eat. I noticed and asked him what was wrong. He said pitifully, "I have to go to the bathroom." I was puzzled. The door to the boy's room was in plain sight. He said "My mommy has to wipe me." I offered to show him how do to that himself, and all was well. The next day, his mother met him as usual at the gate of the schoolyard to guide him across the street*, but the two of them were just standing there when I came out. He had evidently pointed me out to her, because she addressed me when I approached. I assumed I was in for a scolding, but I was wrong. She thanked me warmly for caring for and educating her little darling. Despite being an articulate kid, I probably wouldn't have been able to express what I thought of her parenting skills even had I wanted to. I said only, "You could have showed him yourself if you wanted him to know." Her son was merely ignorant. She was dumb. Jerry ______________________________ * At that age, I would go alone by bus and subway to the Museum of Natural History to spend the day. My parents gave me half a dollar for the day; $.20 for four fares, $.25 for lunch in the cafeteria, and a nickle just so. (Usually a candy bar.) -- Engineering is the art of making what you want from things you can get. ����������������������������������������������������������������������� |