Re: Subjective attenuation of low frequencies? (Bob Masta )

Subject: Re: Subjective attenuation of low frequencies?
From:    Bob Masta  <masta(at)UMICH.EDU>
Date:    Sat, 9 Jun 2001 08:20:24 -0400

On 8 Jun 01, at 12:39, Volpe, Christopher R (CRD) wrote: > [regarding the reason bass sounds are perceived to diminish with repeated listening to a vinyl > recording..] > > |> 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). > > I realize that this is tangent to the question at hand, but... > > This is counter-intuitive to me. The wearing of the groove should act as a smoothing operator, > effectively reducing the *high* frequency components, not the low frequency ones. Or am I missing > something? > You are exactly correct, and this was indeed a known problem with records. There is no possible way the large low-frequency excursions could be reduced without taking the highs first. As an aside here, you may be interested to know that proper operation involves the tiny stylus tip generating such high contact pressure that it actually melts the vinyl microscopically at the point of contact. Even though the tracking forces are only a gram or so, the contact area is so small that the pressures can easily run into 1000s of PSI. This bears on the issue at hand because for a while some audiophiles were playing their records under a surface film of water, which seemed to reduce the surface noise. It did: The water interfered with the proper melting and natural cooling, and caused the vinyl to be torn away from the contact area. The high-frequency signals were thus removed right along with the hiss! Robert Masta tech(at) D A Q A R T A Data AcQuisition And Real-Time Analysis Shareware from Interstellar Research

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