Re: linear phase
rednewguy,
Linear phase means that in the passband, the phase shift is directly proportional to frequency, i.e., the phase shift varies linearly with frequency. Phase linearity is important for preserving the waveforms of complex (non-sinusoidal) signals. For example, consider a waveform consisting of a fundamental and a third harmonic. If the fundamental is shifted bye -10 radians, and the third harmonic is shifted by -30 radians, the output will be a delayed version of the input. The output will be delayed by an amount equal to 10/wo, where wo is the radian frequency of the fundamental. The waveshape of the output will be identical to the waveshape of the input.
~
FIR filters can have the linear phase property. A necessary and sufficient condition for phase linearity is the the summing coefficients be symmetrical about the center coefficient. For example, if the coefficients are c0, c1, c2, c3, c4, then if co = c4 and c1 = c3, then the filter will be phase linear. If this symmetry condition is not met, then the fir filter will not be phase linear.
Regards,
Kral