ScopeFIR creates two primary types of plots: Frequency Response and Impulse Response.  Frequency Response plots show a graph of the FIR filter magnitude or phase response as a function of frequency. Impulse Response plots show a graph of the FIR filter impulse responses as a function of time, which, in effect, is a plot of the FIR filter's coefficients.

Frequency and Impulse Plots graph a selected FIR filter type from among Inphase, Quadrature, I and Q, or Complex.  Most FIR projects will contain only a "real" filter, which is designated as Inphase, so that will be the only available filter choice.  However, if you turn a real filter into a complex filter via mixing, the other filter types can be plotted.  Quadrature plots the "imaginary" filter; I and Q plots the real and imaginary filters as if they were two separate real filters, and Complex plots the real and imaginary filter as a single complex filter.

Along with the filter type, you can select a magnitude or phase response to plot.  See Frequency Responses and Impulse Responses for details.

Frequency Response Plots

Frequency Response plots are a primary tool for determining if your FIR filter design does exactly what you want.

The Frequency Response plot appears in the lower-left of ScopeFIR's four-panel design window.  However, if you would like to see the plot in a larger window, you can click on the Frequency Response button on the toolbar, or select one of the Frequency Response choices from the View menu or the plot's right-click menu.

By default, Frequency Response magnitudes are shown in Decibels (dB), and phases are shown in degrees.  Decibels are clipped at a minimum dB value which is -110 dB by default.  This feature prevents nulls in the magnitude response from consuming the vertical resolution of the plot. You can change the clipping value via Minimum dB on the FIR menu,

Although dB units are commonly used to view magnitude, you can see the magnitude response in linear units, if you like, by selecting  Properties on the Frequency menu and un-checking Magnitude in dB.

Impulse Response Plots

Impulse Response plots are generally less imporant than Frequency Response plots, but they can help you determine if your filter design meets certain requirements you might have about the FIR coeffients themselves.  For example, hardware-based FIR implementations typically are limited in magnitude of the coefficients they can process.  Also, some FIR specifications require certain coeffients to have special values such as zero.

The Impulse Response plot appears in the lower-right of ScopeFIR's four-panel design window.  However, as with the Frequency Response plot, if you would like to see the plot in a larger window, you can click on the Impulse Response button on the toolbar, or select one of the Impulse Response choices from the View menu or the plot's right-click menu.