The Import/Boxcar Editor is simply a handy interface that allows you to do two common, though different, operations on an empty FIR filter design. It lets you:
The Import/Boxcar Editor is shown below:
Sometimes you find yourself wanting to use ScopeFIR's powerful filter analysis and modification facilities to examine the characteristics of a FIR filter that was not designed by ScopeFIR. To import a filter:
A " boxcar" filter--sometimes also called a " comb" or " moving average" filter--is a FIR filter whose coefficients all have the same value. This is desirable in certain applications. For example, a boxcar with N taps can be implemented simply by adding the last N samples of a signal together--no multiplier is needed.
All boxcar filters have a lowpass response, and the cutoff frequency of a boxcar decreases as the number of taps increases. Compared to a FIR whose taps can have any value, a boxcar generally does not perform as well for a given number of taps. But that's the price of simplicity.
The Import/Boxcar Editor provides a Frequency Response List which lets you see the exact attenuation of your filter, in dB, at specific frequencies.
If the Automatic option is enabled, ScopeFIR will show you the frequency magnitude response at zero and at half the Sampling Frequency. The Frequency Response List is refreshed whenever you Import Coefficients. (See Using the Frequency Response List for more information.)
When you save your project, the FIR coefficients, the Sampling Frequency, and the Frequency Response List are all saved in the project. Note, however, that if the underlying data file from which you imported changes, you must import it again.
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