SUMMARYIn the field of digital signal processing, there are cases in which the frequency characteristics must be changed instantaneously in response to the processing objective. A filter whose characteristic can be varied instantaneously is called a variable filter. Many reports are available on the design of FIR digital filters with a variable passband. However, it appears that there are no publications on the design of an FIR digital filter in which the portion of the stopband with high attenuation can be varied. In this paper, a design method is proposed for an FIR digital filter using spectral parameters that make the portion of the stopband with high attenuation variable. For the design, the successive projection method with a simple algorithm is applied. A filter with an almost equal-ripple profile for the entire amplitude characteristic is designed by varying the spectral parameters. As a result, it is possible to obtain amplitude characteristics close to those of the filter solved by the Remez algorithm for specifications that change instantaneously from time to time. Finally, a design example is presented to confirm the effectiveness of the present approach.
Several applications in digital signal processing demand variable digital filters with arbitmy variable frequency response. However, the design method of filtm having variable piecewise large attenuation characteristics in the stopband is not proposed. This paper describes the design method of variable FIR digital filters having changed piecewise large attenuation characteristics in the stopband. The basic idea is to represent the coefficients of variable transfer function as the polynomials using spectral parameter. We design each filter with difference stopband attenuation by successive projections method. Then we approximate the obtained filter coefficient by the polynomials using spectral parameter in the least-square sense.
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