Okay, officially my head is spinning.
As the trio of
@JP,
@USER and
@morillon provide the necessary and unvarnished glimpse of "
uncontrolled variables that make this (approach, or test)
non-conclusive" for getting at THD or IMD for our experiment. Much of this appears from my read to reside in the test medium itself, a vinyl record designed by CBS, Audio Technica, Clearaudio, JVC, or others. Those press initially in likely a 1,000 disc run will not be identical to the last 100, or they are warped as
@JP noted of the CBS test records available on the popular auction site. Calibration is required. Or they are as rare as hen's teeth for which a bidding war will make using one somewhat untenable for such an experiment. Or they don't contain the requisite tracks to do these types of evaluations. To summarize, quoting
@USER, "...there is, in effect,
no good test record..." Message received.
Sorry to tout two articles both published in The Vinyl Press, but I do so for context. The first was published in September 2018, entitled, "
The Curious Case Of Record Cleaning In The Quest For Sonic Perfection", and the second was published in May 2019, entitled, "
The Finish Line for Your Phonograph Stylus…" These articles are survey pieces that in essence collect prior research and put that historic work together with contemporary anecdotes into a narrative of personal discovery. In the included historic work are two fundamental themes: reality of stylus wear, and record cleaning to minimize stylus wear. The former is supported by imaging of progressively worn styli tips. In the course of examining those, degradation in sonic qualities is mentioned, but rarely is it the focus or shown with the type of frequency charts shown by
@USER. Yet these two aspects of vinyl record playing go hand-in-glove.
The aforementioned JICO 3% THD claim opened the door to the possibility for verifiable measurements. In many ways I now better appreciate, the benchmark is a rabbit hole, sorry
@morillon, fraught with issues. In January 2016, I met Hans Weedon, who holds crucial patents for logarithmic analog-to-digital conversion, from when he was at Analogic Corporation. We spent 10 days together and have communicated since. He regaled me with many stories about these AD devices, the pros and cons, the flaws, and about audio in general. He knew of my passion for vinyl records and my hobby of converting the music from them to digital formats. Because he tested such things, he shared with me that he took new and pristine vinyl records and measured their frequency response on the first play and subsequent plays. He noted that after
one single play, a vinyl record loses forever its highest frequencies – likely inaudible to humans. Subsequent plays further degrade records, but to an increasingly lower degree. AC had the necessary equipment to make these measurements. I though we could measure those trends with some work, especially after seeing the skills developed herein. That, perhaps naively, is why we captured 96/24 dubs of three sides of vinyl.
As stated (sorry to be redundant), we are hoping to couple evidence of progressive physical wear on a stylus tip with evidence of increased distortion from the worn stylus, regardless of how one measures it. And as a bonus, measure increased degradation of the signal from a worn record.
@Ray Parkhurst absolutely has developed the skills, techniques, and equipment to properly evaluate this physical wear. He has found the pitfalls, as one poster noted at the beginning of this thread, and he has the experience to avoid these. But as mentioned in prior historic research, we want to close the loop, to be complete. We wanted to couple actual physical stylus wear with audible changes from the cartridge as a consequence of that wear, and even attempt to see both physical degradation within a vinyl groove and increased distortion.
My read from
@JP,
@USER, and
@morillon is that task is much, much easier said than done.
Edit: just noticed that Ray has addressed some of this. Yeah, I'm wordy, because I want to be clear and complete.