I know of no other filter design software with that powerful capability. This means you can monitor the output of a designed filter (in both the time and frequency domains) in real-time as you manually manipulate the filter's frequency response 'markers' or z-plane poles or zeros. For example, you can design a lowpass IIR filter and then manually position a pair of conjugate zeros so that they reside at 60 Hz (or 50 Hz) to provide a deep frequency response notch in order to highly attenuate AC power-line spectral noise.Īs if the easy filter design capability weren't enough, the software designers also provide a way for the user to specify test signals that are applied to the input of the designed filter. The Filter Designer allows you to design specialized filters by way of manipulating the pole/zero locations using your computer's mouse. Once a high-order IIR filter is designed it can be converted to a cascade of 2nd-order biquad IIR sections to enable a stable filter implementation using fixed-point arithmetic. That will automatically change the frequency response curve and the z-plane pole/zero locations, as well as update the filter's coefficients. To change the filter's frequency-domain performance you merely use your computer's mouse to click on the little red squares ("Markers") and move them around in the frequency response plot. The magnitude response of the filter is displayed in the Filter Analysis area after the coefficients are computed.This article is available in PDF format for easy printing After setting the design specifications, click the Design Filter button at the bottom of the GUI to design the filter. Wpass and Wstop, in the Magnitude Specifications area are positive weights, one per band, used during optimization in the FIR Equiripple filter. Enter 0.2 for wpass and 0.5 for wstop in the Frequency Specifications area.Ħ. Select Normalized (0 to 1) in the Units pull down menu in the Frequency Specifications area.ĥ. Increasing the value creates a filter which more closely approximates an ideal equiripple filter, but more time is required as the computation increases. The FIR Equiripple filter has a Density Factor option which controls the density of the frequency grid. Select Specify order in the Filter Order area and enter 30.ģ. In general, when you change the Response Type or Design Method, the filter parameters and Filter Display region update automatically.Ģ. Select Lowpass from the dropdown menu under Response Type and Equiripple under FIR Design Method. We will use an FIR Equiripple filter with these specifications:ġ. We will design a low pass filter that passes all frequencies less than or equal to 20% of the Nyquist frequency (half the sampling frequency) and attenuates frequencies greater than or equal to 50% of the Nyquist frequency. You can right-click or click the What's This? button to get information on the different parts of the tool. The tool includes Context-sensitive help. Other panels can be displayed in the lower half by using the sidebar buttons. It controls what is displayed in the other two upper regions. The Design Panel, in the lower half is where you define your filter specifications. The lower half of the GUI is the interactive portion of Filter Designer. The Filter Display region, in the upper right, displays various filter responses, such as, magnitude response, group delay and filter coefficients. It also provides access to the Filter manager for working with multiple filters. The Current Filter Information region, in the upper left, displays filter properties, namely the filter structure, order, number of sections used and whether the filter is stable or not. The upper half of the GUI displays information on filter specifications and responses for the current filter.
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