Electromagnetic impulse noise which is harmful to signal measurement or transmission of information, is smoothed by the orthogonal transform processor. The idealized impulse noise with infinitesimal duration and Gaussianly-distributed amplitude shows the same spectral characteristics as white Gaussian noise. Optimal correlation detector against such noise is easily realized by the orthogonal transform processor. Photoelectric pulse signals disturbed by the impulse noise from the power supply can be well detected through the Walsh waveform analyzer. Also, orthogonally-synthesized signals can be demodulated with firmly-suppressed impulse noise, where both the statistical and instantaneous SNRs are superior to those in the usual PCM transmission system.