Data AcQuisition And Real-Time AnalysisScope - Spectrum - Spectrogram - Signal Generator
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Noise Band Window
Daqarta derives the FIR tap constants using a simplified Fourier series approach that assumes an infinite number of taps. Since the number of taps is actually limited, the filter response would have peaks and dips. This is similar to the way that an FFT looking at a truncated (instead of infinite) waveform would show a spectrum with peaks and dips. The cure is the same in both cases: Window functions. In the FFT case the spectral window function is used to taper the input waveform gently to zero at the ends; in the FIR case the window tapers off the values of tap constants near the ends of the delay line.
Just like spectral windowing, there are lots of possible window functions and lots of opinions on which to use under what conditions. The default here is a Hann (Hanning) window, but you can toggle to Hamming, Blackman, Blackman Exact, Blackman-Harris, or Rectangular (no window at all). The best bet is to fool around with this control while doing spectral averages of the output, to get familiar with the various response shapes.
Note that unlike the Taps control, there is no performance or memory penalty related to the Window selection. It doesn't change the number of taps or size of lookup tables, only the values in the tables.
0 = Rect = Rectangular 1 = Hann = Hann 2 = Hamm = Hammning 3 = Bkmn = Blackman 4 = BkEx = Blackman Exact 5 = BkHr = Blackman-Harris
Note that the numbers do not match those of the corresponding Spectrum Window Functions of the same names.
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