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To investigating the capabilities of human beings to differentiate between tactile-vibratory stimuli with the same fundamental frequency but with different spectral content, this study concerns discrimination tasks comparing audio and haptic performances. Using an up-down 1 dB step adaptive procedure, the experimental protocol consists of measuring the discrimination threshold between a pure tone signal and a stimulus composed of two concurrent pure tones, changing the amplitude and frequency of the second tone. The task is performed employing exactly the same experimental apparatus (computer, AD-DA converters, amplifiers and drivers) for both audio and tactile modalities. The results show that it is indeed possible to discriminate between signals having the same fundamental frequency but different spectral content for both haptic and audio modalities, the latter being notably more sensitive. Furthermore, particular correlations have been found between the frequency of the second tone and the discrimination threshold values, for both audio and tactile modalities.