Spider DSA User’s Manual
318
As shown in the pictures, different windows produce different filter performance,
i.e., different attenuation of the main lobe and side lobes. The best data window is
the one that best suits your specific application.
Remez Filters
The Remez Filter is a different method for designing an FIR filter. It is more
computationally intensive than the data window method. A Remez filter is
generated with iterative error-reducing algorithms designed to reduce the pass-
band error. In addition to allowing stop-band ratio and frequency definition, the
Remez filter also allows the "Ripple Ratio" to be defined as a user specified
parameter.
The figure shows an example of a filter design using the Remez method in the
EDM software. The low and high cutoff frequencies are 0.1 and 0.2 relative to the
sampling frequency. The number of filter taps is 67.
Figure 186. Remez FIR Filter design dialog.
The software is intelligent enough to automatically calculate the total FIR filter
length (number of taps) based on these criteria. For example, if the user asks for
very high attention, very small ripple or very sharp transition band, the filter
length will go very high. The user must make tradeoffs between these parameters
so that appropriate filter length can be generated and used.
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