The following is a brief tutorial on how to use ScopeFIR™. After explaining a few things, we design three simple filters, a lowpass, a highpass, and a bandpass.
ScopeFIR designs filters using specifications you provide. For designs which use the Parks-McClellan algorithm, ScopeFIR provides two types of filter specification editors. The first type is the Simple Specification Editor (SSE):
The SSE can edit simple lowpass, highpass, and bandpass filters which have only a single passband. It does not allow access to all possible Parks-McClellan specifications, but is easier to use for basic filter designs.
The second type is the Advanced Specification Editor (ASE):
The ASE is used primarily to design multiple-passband filters, although it also can be used to design single-passband filters. Besides allowing you to enter any number of passbands (and stopbands), the ASE allows you to specify certain additional parameters. It also allows you to design Differentiators and Hilbert transformers.
After you design a filter, both Specification Editors show the actual passband ripple and stopband attenuation.
Now, on to some examples. Our (contrived) mission in these examples is to make a Compact Disk player sound almost as good as a telephone. CD’s use a sampling frequency of 44.1 kHz, and have a frequency response (passband) of about 20 Hz to 20 kHz. Telephones have a frequency response of about 300 to 3000 Hz. That special “telephone sound” you hear when you call Grandma results from this filtering. We accomplish our mission using three filters, a lowpass, a bandpass, and a highpass. You can manually type these into ScopeFIR, or you can just open their Project files, which are included in the ScopeFIR distribution file.