Hi, I'm doing a spectrum analyzer. i collect 4096 samples of data from codec then I stop interrupt and begin fft. The algoritm that I use ( in the ti's dsplib) does not provide a windowing, so I don't understand if would be ok to do some "by-hand weighted windowing" multiplying a window with the frame of data, without implementing an overlap-add function. And secondarily, is right to do a "fake overlap-add" simply multiplying sample with a new window function that is a sum of a window and it's copy shifted? Pictorically MY DATA |--------------||--------------||--------------||--------------| WINDOW (Blackman,triangular, hann...) - - - - - - - - - - - - - - - - - - - - - - - - - - - -
fft and windowing
Started by ●October 26, 2011
Reply by ●October 26, 20112011-10-26
Hi Heavyfranz, All you need to do is to apply a window function to each batch of 4096 samples. Don't use a triangular window though; its only advantage is that it is marginally easier to calculate a triangular function. You mention "overlap add." this technique would be used only if you were intending to implement a filter function in addition to the spectrum analysis you mention. In that case, if you are filtering using FFT-based convolution, it is essential that you do not window the data because windowing would cause severe modulation in the resulting time-domain output of the filter. Regards, John On 27/10/2011 1:50 AM, heavyfranz wrote:> Hi, I'm doing a spectrum analyzer. i collect 4096 samples of data from > codec then I stop interrupt and begin fft. > The algoritm that I use ( in the ti's dsplib) does not provide a windowing, > so I don't understand if would be ok to do some "by-hand weighted > windowing" multiplying a window with the frame of data, without > implementing an overlap-add function. And secondarily, is right to do a > "fake overlap-add" simply multiplying sample with a new window function > that is a sum of a window and it's copy shifted? > > Pictorically > > MY DATA > |--------------||--------------||--------------||--------------| > > WINDOW (Blackman,triangular, hann...) > - - - - > - - - - - - - - > - - - - - - - - > - - - - - - - - > > >