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:

- Import and analyze a FIR filter designed outside of ScopeFIR.
- Create and analyze a very simple type of FIR filter called a
*boxcar*.

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:

- Hit the
*Sampling Frequency*button on the upper left. You will be prompted to enter the numerical frequency and the units of frequency/time. (ScopeFIR needs to know the sampling frequency in order to determine the frequency response of the filter.) - Hit the
*Import Coefficients*button. You will be prompted to locate the file(s) of FIR filter coefficients to be imported. You will then see the characteristics of the filter depicted in ScopeFIR's Frequency/Impulse Response plots and its coefficient editor. You may modify the filter, if you like, using commands in ScopeFIR's FIR menu.

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's *Create Boxcar* button allows you to design a boxcar filter by filling it with a constant. This is simply a shortcut to the Fill Filter With Constant command of the FIR menu.

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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