about filter
| choco | March 8, 2012 - 02:48 | ||||||||||||
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 I have some problem for filter, so I did a simple case to understand it. Another problem is
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| choco | March 8, 2012 - 02:48 | ||||||||||||
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I have some problem for filter, so I did a simple case to understand it. Another problem is
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Joined: 2007-07-19
Location: United States
To start with, don't use X waves when you're doing any kind of signal processing such as filtering, convolutions, or FFTs; it is extremely unhelpful.
Use the wave scaling to set the sampling frequency of the signal (100 Hz in your example)
Now when you select one of these waves to filter, the design frequency (which is the same as the sampling frequency when you choose a wave to be filtered), will be properly set to 100Hz.
Click the Filter dialog's "Help" button to read about the Digital Signal Processing (DSP) terminology such as "design frequency" or "sampling frequency".
An FIR filter with only 3 coefficients isn't going to do very much filtering (a lowpass filter won't reject much), and your test signals have almost all of their energy at very low frequencies, as an FFT of those waves will show.
You also might want to review some basic DSP definitions:
http://www.dspguru.com/dsp/faqs/fir
--Jim Prouty
Software Engineer, WaveMetrics, Inc.