From: onkars on 29 Jun 2010 18:22 Hi, I am looking for an FFT algorithm that can give me a 4096 pt. FFT using two 64 pt. FFTs. Is it the mixed radix FFT? Thank you.
From: Jerry Avins on 29 Jun 2010 18:37 On 6/29/2010 6:22 PM, onkars wrote: > Hi, > > I am looking for an FFT algorithm that can give me a 4096 pt. FFT using two > 64 pt. FFTs. Is it the mixed radix FFT? > > Thank you. I'd like to have a bank account That gives me a $4096 balance for two $64 deposits. Jerry  Engineering is the art of making what you want from things you can get. �����������������������������������������������������������������������
From: onkars on 29 Jun 2010 19:28 >On 6/29/2010 6:22 PM, onkars wrote: >> Hi, >> >> I am looking for an FFT algorithm that can give me a 4096 pt. FFT using two >> 64 pt. FFTs. Is it the mixed radix FFT? >> >> Thank you. > >I'd like to have a bank account That gives me a $4096 balance for two >$64 deposits. > >Jerry > >Engineering is the art of making what you want from things you can get. >����������������������������������������������������������������������� > What i mean "using two 64 pt FFTs" is that there is some reordering and twiddle multiplications between the 2 64 pt FFTs. And of course the whole 4096 pt. FFT will take many cycles. I guess this can be achieved using the mixedradix  i.e. 4096 = 64 x 64. Hence the 1st 64 point FFT will perform 64 number of 64 pt FFTs followed by some reordering and twiddle factor mults (which I intend to learn about) and then finally again 64 number of 64 pt FFTs using the 2nd 64 pt. FFT. Is this the mixedradix? also where can I read the theory about this mixed radix ffts  which will enable me to implement any N (N=P*Q) pt. FFt using P pt and Q pt FFT engines. Thank you.
From: Jerry Avins on 29 Jun 2010 22:12 On 6/29/2010 7:28 PM, onkars wrote: >> On 6/29/2010 6:22 PM, onkars wrote: >>> Hi, >>> >>> I am looking for an FFT algorithm that can give me a 4096 pt. FFT using > two >>> 64 pt. FFTs. Is it the mixed radix FFT? >>> >>> Thank you. >> >> I'd like to have a bank account That gives me a $4096 balance for two >> $64 deposits. >> >> Jerry >>  >> Engineering is the art of making what you want from things you can get. >> > > What i mean "using two 64 pt FFTs" is that there is some reordering and > twiddle multiplications between the 2 64 pt FFTs. And of course the whole > 4096 pt. FFT will take many cycles. > I guess this can be achieved using the mixedradix  i.e. 4096 = 64 x 64. > Hence the 1st 64 point FFT will perform 64 number of 64 pt FFTs followed by > some reordering and twiddle factor mults (which I intend to learn about) > and then finally again 64 number of 64 pt FFTs using the 2nd 64 pt. FFT. > > Is this the mixedradix? also where can I read the theory about this mixed > radix ffts  which will enable me to implement any N (N=P*Q) pt. FFt using > P pt and Q pt FFT engines. Perhaps there is enlightenment here: www.vassilioschouliaras.com/pubs/c39.pdf Jerry  Engineering is the art of making what you want from things you can get.
From: dvsarwate on 29 Jun 2010 22:21 On Jun 29, 6:28 pm, "onkars" <onkar.sarode(a)n_o_s_p_a_m.gmail.com> wrote: > >On 6/29/2010 6:22 PM, onkars wrote: > >> Hi, > > >> I am looking for an FFT algorithm that can give me a 4096 pt. FFT using > two > >> 64 pt. FFTs. Is it the mixed radix FFT? > > >> Thank you. > > >I'd like to have a bank account That gives me a $4096 balance for two > >$64 deposits. > > >Jerry > > > >Engineering is the art of making what you want from things you can get. > > > > What i mean "using two 64 pt FFTs" is that there is some reordering and > twiddle multiplications between the 2 64 pt FFTs. And of course the whole > 4096 pt. FFT will take many cycles. The theory says that a 4096 FFT can be done using 4096x12 multiplications. Some savings can be achieved by careful coding, but N log_2 N is a useful rule of thumb. > I guess this can be achieved using the mixedradix  i.e. 4096 = 64 x 64. > Hence the 1st 64 point FFT will perform 64 number of 64 pt FFTs followed by > some reordering and twiddle factor mults (which I intend to learn about) > and then finally again 64 number of 64 pt FFTs using the 2nd 64 pt. FFT. If you do 64 64point FFTs, that is 64x64x6 = 4096x6 muiltiplications.The next set of 64 64point FFTs also takes 4096x6 multiplications. So, we are up to 4096x12 muiltipications already. Taking into account the re ordering and the twiddle factors that you refer to, your proposed approach may not provide a significant gain. Plus, the programming is that much more complicated, but YMMV. Dilip Sarwate

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