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Subjective attenuation of low frequencies?
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
270 Crown Street
New Haven, CT 06511-6695
Tel. (203) 865-6163, ext. 236
FAX (203) 865-8963