Subjective attenuation of low frequencies? (Bruno Repp )

Subject: Subjective attenuation of low frequencies?
From:    Bruno Repp  <repp(at)ALVIN.HASKINS.YALE.EDU>
Date:    Wed, 6 Jun 2001 13:42:16 -0700

Dear List members: I have received a message from a gentleman who is not a psychologist but has been working in the audio industry. He reported some interesting observations, which I have reproduced below. Has anything similar been found in controlled experiments, and is there any psychoacoustic explanation for the phenomenon (if it is real)? Please, reply to me directly, and I'll forward your responses to the gentleman and summarize them for the List. "The introduction of digital, as opposed to analogue recording techniques, was an eagerly anticipated event in most quarters of the audio world. A phenomenon had been noted whereby the integrity, solidness etc. of bass notes/sounds was perceived as being greatest on first audition of a recorded work, subjectively seeming to diminish on second and subsequent hearings. We supposed that this was due to the mechanical wear produced by the stylus contacing the grooves of the disc, effectively behaving like a cutting lathe, shaving off the groove modulations (which are biggest for bass notes). We were therefore surprised to find that the same subjective assessments repeated using digital (CD) sources, produced the same results. You can try this for yourself at home. Just buy a CD you've never heard before, listen to a track, then play it again, anything from a half hour to a day later. The more times you hear the track, the longer the effect lasts. This suggests that the brain has very strong predictive abilities in the audio domain, especially with regard to low frequency sounds. Working on this assumption, we then repeated the experiment, using a multi-way speaker system and an electronic crossover. This enabled us to time-delay the bass information, while leaving the mid-high frequencies unaffected. The result? No change, but when we introduced randon variations in bass delay time of between 2 and 7 milliseconds, the subjective bass loss effect was cancelled out." Bruno H. Repp Research Scientist Haskins Laboratories 270 Crown Street New Haven, CT 06511-6695 Tel. (203) 865-6163, ext. 236 FAX (203) 865-8963 e-mail: repp(at)

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Electrical Engineering Dept., Columbia University