FIR Filter Design Methods

ScopeFIR can design Finite Impulse Response (FIR) filters using several different methods. Each method has its own set of input parameters, so ScopeFIR provides a "Specification Editor" for each method, thus allowing you full control over the filter's design.

ScopeFIR supports the following filter design methods:

  • Parks-McClellan - This method designs equiripple filters. Equiripple filters are so called because they allow you to trade ripple in the passband against attenuation in the stop band. The Parks-McClellan method is an extention of the Remez algorithm which allows you to design not only filters, but also differentiators and Hilbert Transformers. The Parks-McClellan method allows you to specify many different filter design parameters, so it is very flexible.
  • Windowed Sinc - This design method is less flexible than the Parks-McClellan method, but sometimes can be advantageous because it can produce produce smoother passbands. The Windowed Sinc method is based on the idea that a brick-wall filter in the frequency domain corresponds to a "sinc" function (sin x / x) in the time domain. However, sinc functions have infinite length. Therefore, the sinc function needs to be truncated to form the coefficients of a Finite Impulse Response filter. This method simply designs a brick-wall filter with the corner frequencies specified, then uses one of the standard data windows to truncate the filter to the specified length.
  • Raised Cosine - Raised Cosine filters are a special filter type of filter which is widely used in digital data applications. ScopeFIR can design both Raised Cosine filters and a closely related type of filters, Root Raised Cosine.
  • Lth-Band (Nyquist)  - This method designs filters which have the property that (N-1)/2L coefficients are zero, which makes them computationally-efficient. ScopeFIR's Lth-Band design method really is just an interface to some of its other design methods, with the Lth-Band constraints automatically imposed.
  • Import/Boxcar - This allows you to import and analyze a FIR filter which has been designed outside of ScopeFIR. It also allows you to design Boxcar filters.
  • Maximally Flat - As the name suggests, this method allows you to design filters with whose passbands are as flat as is theoretically possible for the given specifications.
  • CIC -This method allows you to design and analyze Cascaded Comb-Integrator (CIC) filters.

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