High Quality Content by WIKIPEDIA articles! The equation above for the output of the ZOH can also be modeled as the output of a linear time-invariant filter with impulse response equal to a rect function, and with input being a sequence of dirac impulses scaled to the sample values. The filter can then be analyzed in the frequency domain, for comparison with other reconstruction methods such as the Whittaker Shannon interpolation formula suggested by the Nyquist Shannon sampling theorem, or such as the first-order hold or linear interpolation between sample values.