Last week my blog was a comparison of 7“ 45 RPM singles to 12” 33/13 RPM albums. After reading the blog, my college roommate, Tillman Bunch asked me a question that I thought about some back in the day but had completely forgotten about; “Rick, was there a difference in the quality of an inside track vs an outside track on a 33 and a third album as a rest of wear or speed?”
My answer to him was “Tillman, I could never hear a difference in quality but the linear velocity of a needle in a groove is lower the closer to the center of the record it gets. I'm gonna have to research this to see exactly how much slower it is but it will be more of a difference on an album than it is on a 45, because it is related to the radius of the individual groove.”
I am apologizing in advance to everyone for the “nerdiness” of today’s blog but here goes. I am breaking out my high school trigonometry and doing that research. OMG there goes that internet meme!
So in the raw physical world without any processing, the linear velocity of the needle is the distance that the needle travels in a unit of time. That is the circumference of the groove segment in which the needle is tracking. Note I say groove segment because there is only one groove on a record, regardless of whether or not there is one or many tracks on that side. If there were more than one, you would have to manually lift the tone arm at the end of each track and place it on the next.
Let’s look at a 12” 33 1/3 RPM record first. I pulled a random LP out of my collection. It was Linda Ronstadt’s “Living in the USA” Electra Asylum released in 1978. The album was Ronstadt's third (and last) No. 1 on the Billboard album chart. I broke out my trusty ruler and measured the radius from the center of the hole to the outside edge of Track #1 of the “B” Side; “All That You Dream”; it was 5.75 inches. From the center of the hole to the edge of the last track, “Love Me Tender,” the radius is 2.5625 inches. Multiplying these values by 2 and then by the value of pi, we get a circumference of 36.13 inches and 16.1 inches respectively. Multiplying these numbers by 33 1/3 gives us the linear velocity in inches per minute; 1204.26 and 536.38 respectively. Divide each by 60 and we get 20.07 IPS and 8.94 IPS. So by the time the needle reaches the inside track of the record it is traveling through the groove at 44.6% of the velocity it was tracking on the outside edge of the record.
My random pick for a 45 RPM record was “Breezy” by The Tokens. Without putting you through those mathematical calculations again I’ll tell you that the linear velocity of the needle on the outside edge of the track is 14.31 IPS and 10.9 IPS on the inside edge. On a 45 RPM record the needle is traveling through the groove on the inside edge of the track at 76.1 % of the velocity it was traveling on the outside.
“Now wait a minute!” I hear you saying, how can this be? Won’t the sound of the record be “dragging” by the time you reach the inside edge of the groove. The reason it doesn’t is that master record was recorded the same way that it is played. But instead of the needle picking up the sound it is etching it into the vinyl. So the same trigonometry applies in the recording phase. The only thing different is the length of the groove that is occupied by a single note. I.E. on a 45 RPM record a note that occupies one inch of groove space on the outside of the record will occupy a little over an inch and a third of groove space on the inside track of the record.
OMG, all this is making my head hurt.
But Tillman’s question is about the quality of the sound; will that change.
I suppose if one were to break out a bunch of audio test gear such as an oscilloscope, noise detectors and distortion analyzers, we would be able to measure differences between the beginning and end of the track on a record but joyfully there are few human ears that could detect that difference. As for me, I’m too interested in the music to care much about that minutia.
By the way, just in case you are wondering about CDs. CDs spin at an angular velocity of 500 rpm when read from the center and 200 rpm when read near the circumference to provide for a constant linear velocity that has been standardized at 42.2 to 55.1 IPS.
OK, if your head hurts like mine does, that is enough of that. I’m gonna go crash in my easy chair and contemplate the error of my ways. Oh MY!
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