I have the impulse response (from the filter coefficients) of an FIR filter obtained from MATLAB's "interp" function using the command:
[y, b] = interp(x, 5); % where b contains the interpolation filter coefficients.
When I plot the magnitude response of this filter using "freqz" in MATLAB, I get the following
What do those side lobes between 0.5 and 0.7 (x pi rad/sample) and 0.9 and 1 (x pi rad/sample) mean for my FIR filter? Why are they there?