Csontos and Peterayers hear exactly what I hear.
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Lewm, sorry we haven't explained this in a way that helps you understand this as a timing issue. Thanks for hanging in there.
Of course you're right that the spinning platter controls the timing of the MUSIC. If a TT runs slow or fast, the pace and pitch of the music will be off. If TT speed varies, we hear pitch shifts.
With SRA we're talking about a timing on a much smaller scale: the *relative* timing of the component parts of a SINGLE NOTE. This kind of timing has nothing to do with pitch or rhythm. TT speed does not affect it, SRA changes alter the internal timing of each note even when TT speed is perfect. In fact, they're easier to hear on a TT that maintains highly accurate speed.
Peter wrote,
If the fundamental is being obscured by the harmonics, the harmonics are arriving too early. I hear this when the arm is too low in the back. If the fundamental occurs unnaturally early, or there appears to be a minute lag before you hear the harmonics after the fundamental, then the arm is too high
I think he got the arm positions reversed, but the effects he described are exactly what I hear.
As for a mechanism to explain this, I can only offer conjecture.
Fact: the cutting stylus had *some* specific SRA. This results in a unique cross-section for each and every complex set of groove modulations that make up what we call a "sound".
Assumption: to trace each cross-section exactly, the playback stylus must have the same SRA.
If the arm is too high at the pivot, the tip of the stylus will encounter each modulation before the the top of the stylus does, ie, too early. If the arm is too low at the pivot, the tip of the stylus will be slightly behind the top of the stylus, ie, too late. In either case, the stylus will "slur" across the modulation instead of encountering each part of it simultaneously.
If the playback stylus "slurs" across each modulation rather than tracing it *exactly* as cut, the aural effect is that harmonics arrive either too early or too late RELATIVE TO their fundamental.
I would not argue that this is necessarily what is occuring, but this is what it sounds like.
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Raul mentioned dynamics. Optimal SRA provides optimal micro-dynamics. If the playback styles traces each modulation as cleanly as possible, cantilever excursions will match the path of the cutting head as closely as possible. To the extend the playback stylus "slurs" across modulations, cantilever excursions will be reduced and slurred in time, reducing dynamics.
I find this harder to hear than timing errors in fundamental vs. harmonics, but Paul finds it easier. With regard to SRA changes, I believe he and Raul hear similar things.