On 2/26/14 10:08 PM, Eric Jacobsen wrote:> On Wed, 26 Feb 2014 16:07:15 -0600, Tim Wescott > <tim@seemywebsite.really> wrote: > >> On Wed, 26 Feb 2014 21:08:41 +0000, glen herrmannsfeldt wrote: >> >>> Tim Wescott<tim@seemywebsite.really> wrote:...>>>> Keep in mind that a[0 ... N/2] = a[N-1 ... N/2]*, where a* denotes the >>>> complex conjugate of a. This (together with knowing that Im(a[0]) == >>>> Im(a [N/2] == 0) reflects the fact that you only put in N non-zero >>>> points (because the N imaginary samples were zero), so you only get out >>>> N unique points. >>> >>> That says why a[N/2] is special, but the OP asked about a[N/2+1]. >>> (Where the first element is a[0].) >> >> We all missed that. >> >> Hey! OP! You meant a[N/2]. Really. a[N/2 + 1] is just the complex >> conjugate of a[N/2 - 1]. Or your indexing is off. Or something. > > I didn't miss it, I added the caveat about "depending on your > coefficient numbering". I didn't point it out because I thought the > only candidate in the region for specialness is the symmetry point, so > I figured it was a typo or a numbering issue.it's because of MATLAB (or Octave or R or whatever fixed 1-origin indexing in whatever tool). blame it on err, ... MATLAB (Cleve, i won't name names.) jadedly, -- r b-j rbj@audioimagination.com "Imagination is more important than knowledge."
General FFT question
Started by ●February 26, 2014
Reply by ●February 27, 20142014-02-27
Reply by ●February 27, 20142014-02-27
On 2/27/14 3:27 AM, Markus Grunwald wrote:> Hello to all who answered :) > > Thank you very much, your Answers were most helpful. The one that I > understood easily was clay's "Think of sampling a cosine every multiple > of 180 degrees." while the others helped to understand further. > > And you're right, I got my indexing wrong.and we understand why. it's not your fault. but i won't say whose fault it is. -- r b-j rbj@audioimagination.com "Imagination is more important than knowledge."
Reply by ●February 28, 20142014-02-28
On Thu, 27 Feb 2014 14:14:29 -0500, robert bristow-johnson wrote:> On 2/27/14 3:27 AM, Markus Grunwald wrote: >> Hello to all who answered :) >> >> Thank you very much, your Answers were most helpful. The one that I >> understood easily was clay's "Think of sampling a cosine every multiple >> of 180 degrees." while the others helped to understand further. >> >> And you're right, I got my indexing wrong. > > and we understand why. it's not your fault. but i won't say whose > fault it is.It's all our faults. Clearly the indexing should start at 'a' and go from there. -- Tim Wescott Wescott Design Services http://www.wescottdesign.com
Reply by ●February 28, 20142014-02-28
On 2/28/14 6:06 PM, Tim Wescott wrote:> On Thu, 27 Feb 2014 14:14:29 -0500, robert bristow-johnson wrote: > >> On 2/27/14 3:27 AM, Markus Grunwald wrote: >>> Hello to all who answered :) >>> >>> Thank you very much, your Answers were most helpful. The one that I >>> understood easily was clay's "Think of sampling a cosine every multiple >>> of 180 degrees." while the others helped to understand further. >>> >>> And you're right, I got my indexing wrong. >> >> and we understand why. it's not your fault. but i won't say whose >> fault it is. > > It's all our faults. Clearly the indexing should start at 'a' and go > from there.but neither you nor i have put out a math modeling tool along with a toolbox directed toward signal processing. i don't see how "it's all our faults". -- r b-j rbj@audioimagination.com "Imagination is more important than knowledge."
