On Jan 13, 3:52 am, "antenna404" <wanfa...@163.com> wrote:> hi Kumar Vijay Mishra > I am sure that I have made my data Hermitian symmetric. > just like this: > 1-j*1,2-j*2,3-j*3,0,3+j*3,2+j*2,1+j*1. > but after doing IFFT,the output is still a complex sequence.But your data is, in fact, not complex conjugate symmetric! The correct sequence will be: [0, 1-1i, 2-2i, 3-3i, 3+3i, 2+2i, 1+1i]. This is because the dc component is NOT included while considering the above-said symmetry of the sequence. Kumar Vijay Mishra.
How to use IFFT to get the system impulse response?
Started by ●January 11, 2008
Reply by ●January 15, 20082008-01-15
Reply by ●January 23, 20192019-01-23
เมื่อ วันจันทร์ที่ 14 มกราคม ค.ศ. 2008 19 นาฬิกา 46 นาที 55 วินาที UTC+7, Greg Berchin เขียนว่า:> On Jan 13, 5:52 am, "antenna404" <wanfa...@163.com> wrote: > > > I am sure that I have made my data Hermitian symmetric. > > just like this: > > 1-j*1,2-j*2,3-j*3,0,3+j*3,2+j*2,1+j*1. > > but after doing IFFT,the output is still a complex sequence. > > Just as an experiment, try structuring your data set like > > "0, 3+j*3, 2+j*2, 1+j*1, 1-j*1, 2-j*2, 3-j*3", > > if your FFT size is odd, or > > "0, 3+j*3, 2+j*2, 1+j*1, 4, 1-j*1, 2-j*2, 3-j*3", > > if it is even, and run that through Matlab's IFFT. > > Greg
Reply by ●January 23, 20192019-01-23
Hi Greg, Could u explain why u add 0 and 4 to the complex hermitian conjugate when a number is even. THanks.
Reply by ●January 23, 20192019-01-23
On Tuesday, January 22, 2019 at 11:28:16 PM UTC-6, won...@gmail.com wrote:> Could u explain why u add 0 and 4 to the complex hermitian conjugate when a number is even.The reason to put *values* at DC and Fs/2 is because the DFT of a real sequence with an even number of elements is conjugate-symmetric about DC and Fs/2 -- they serve as "pivot points" for the symmetry. The reason that the values at DC and Fs/2 are *real* is that the only way a number can be its own complex conjugate is if it's real. The reason that the values are "0" and "4" has been lost to history -- this is, after all, an eleven year old thread. - Greg
Reply by ●January 23, 20192019-01-23
On Wednesday, January 23, 2019 at 8:01:23 AM UTC-5, Greg Berchin wrote:> On Tuesday, January 22, 2019 at 11:28:16 PM UTC-6, won...@gmail.com wrote: > > > Could u explain why u add 0 and 4 to the complex hermitian conjugate when a number is even. > > The reason to put *values* at DC and Fs/2 is because the DFT of a real sequence with an even number of elements is conjugate-symmetric about DC and Fs/2 -- they serve as "pivot points" for the symmetry. The reason that the values at DC and Fs/2 are *real* is that the only way a number can be its own complex conjugate is if it's real. The reason that the values are "0" and "4" has been lost to history -- this is, after all, an eleven year old thread. > > - Gregwow an 11 year gap and the conversation picks right up where it left off :-) mark
Reply by ●January 24, 20192019-01-24
เมื่อ วันพุธที่ 23 มกราคม ค.ศ. 2019 20 นาฬิกา 01 นาที 23 วินาที UTC+7, Greg Berchin เขียนว่า:> On Tuesday, January 22, 2019 at 11:28:16 PM UTC-6, won...@gmail.com wrote: > > > Could u explain why u add 0 and 4 to the complex hermitian conjugate when a number is even. > > The reason to put *values* at DC and Fs/2 is because the DFT of a real sequence with an even number of elements is conjugate-symmetric about DC and Fs/2 -- they serve as "pivot points" for the symmetry. The reason that the values at DC and Fs/2 are *real* is that the only way a number can be its own complex conjugate is if it's real. The reason that the values are "0" and "4" has been lost to history -- this is, after all, an eleven year old thread. > > - GregThanks Greg for your explanation.
