Influence of MLS signal recording on various mediums

Maximum length sequence (MLS) technique represents widely used technique for measurement of impulse responses. Since the impulse response is extracted by cross-correlation between the excitation signal and measured response, the distortions of these signals can significantly influence the measurement results. Possible distortions of the excitation signal can be obtained by its recording on various mediums and by its reproduction from the mediums. The influences of these distortions on impulse responses are investigated in the measurements of the responses of both the part of measurement system and the room, and the results are presented here. It is shown that analogue recording of the excitation signal on magnetic tape significantly reduces the peak-to-noise ratio (PNR) of impulse response or even results in inability to extract the impulse response and it can be completely useless in MLS technique. Digital recording of the excitation signal can also result in the reduction of the PNR, but this reduction is considerably smaller.