bals,
A linear phase filter is a filter for which the phase shift is a linear function of frequency. For example, if the phase shift is X degrees at frequency F, then the phase shift will be nX degrees at a frequency of nF. It is possible to achieve exact linear phase with a FIR filter. However, not all FIR filters have the linear phase property. Certain symmetry or anti-symmetry requirements of the filter coefficients are required for linear phase response. For example, for a filter with an odd number of taps (coefficients), if the coefficients are symmetrical with respect to the center tap, then the filter will have linear phase. Meeting this requirement does not, however, guarantee that the amplitude response with respect to frequency will be desireable. For a concise description of coefficient symmetry/anti-symmetry requirements, see
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**broken link removed**
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For a practical method of linear filter design, search for "Parks-McClellan"
Regards,
Kral