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The surface roughness, known to influence the recording and play-back properties of magnetic recording media, was interferometrically measured of a series of VHS video tapes. A strong correlation (r>.95) was found between both the signal outputs and noise of these tapes with rms surface roughness. The measured short waveloength rf output was shown to decrease with increasing surface roughness in a manner consistent with three theoretical models. A multiplier of 2.7 times the interferometrically measured rms surface roughness is equal to the calculated head-to-tape spacing of these tapes.