As with the general symmetric filter case, if the combination of rate and number of filter taps results in a subfilter which is not fully populated with coefficients, the reorganization of the filter coefficients results in a change in the phase response of the filter. The impulse response is shifted by several output samples as a result. In the 14 tap, interpolate by 4 case, padding a zero coefficient to the front of the coefficient response would be required to align the phases such that symmetry can be exploited, resulting in a smaller implementation, but this results in a different phase response for the filter. The methods to avoid this change in response, if such a change cannot be accommodated in your application system, are also similar to the general symmetry case; you can either force non-symmetric structure implementation or make use of the extra coefficients which can be supported in the structure. This Figure shows several example cases in and is extensible to larger filters.
