Why do vinyl records sometimes sound less clean towards the inner diameter?

Did you ever want to know what happens in your grooves, why there are 33 and 45 rpm records, and why the hell they have a round shape…? Well, you found the man to ask your questions. Loop_o, the master of the grooves, devoted vinylcutter, musician and enthusiast will answer your questions related to vinyl every month. So get deeper into the groove with our 101 on vinyl!

Malte Noack from Hong Kong asks:

“Dear LOOP-O, I was always wondering why do vinyl-records sound less clean towards the inner diameter sometimes.”

Loop-O says:
 
Dear Malte: We all know that a vinyl record is a wonderful medium with a great sound and possibilities.
If treated right you can achieve recordings with a frequency spectrum beyond the specification of a digital compact-disc.
But besides that, Vinyl also has its physical limitations. So before the era of digital audio the frequency range of a recording to be cut onto a master-lacquer disc was much wider than with a common digital file these days. The difference is in the energy of the frequency range. Since we are able to produce audio-files at the digital domain we get very complex signals far beyond any acoustic signal. Therefore we’re constantly about to max out the limitations of a vinyl record.

One of these limitations are trebles. So sometimes a vinyl-record has a loss of treble towards the inner diameter. This effect is getting obvious with some of your 12 inches with only one track, cut over the whole side at 33 rpm. Simply jump with the needle from the start of the record to its end. In the worst case you experience distortions at some sibilance sounds.

So where is this coming from and how we can avoid it?

Basically its because of the geometry of the grooves at the cutting as well the playback stage.
To understand this you have to know that the record groove is simply a physical representation of the sound wave. So a high frequency tone with 10.000 hertz forces the cutting-stylus to cut and the pick-up to play-back a record-groove with 10.000 curvatures per second.

The best and common picture to illustrate this is to imagine the groove as a river with the pick-up as a boat traveling that river at a certain speed. As long as the curves of the river are long drawn-out, which represents a low tone signal, your boat can travel and stay easily parallel to the riversides.

But imagine you get very tight curves, which represent a high tone signal, it gets more difficult for the boat to get through that river without cutting the corners. At the point where the density of the curvatures are tighter than the length of your boat we get a problem. As this example illustrates the record groove – it means that the groove-curvatures are closer together than the size of our cutting-stylus and our pick-up’s tip.

At the cutting-stage it means that in the worst case the stylus is wiping out parts of the groove with its back that he just cut before.
Of course the same relation between the cutting-stylus and the groove-geometry appears to the pick-up at the playback side. Here the tip goes over the curves instead through them which results in a loss of high frequencies and distortion.

How we can translate that example to the diameter of our vinyl record?

While a record is spinning always at the same speed (33 1/3, 45 or 78 rpm) the diameter of the actual played groove is getting lower with the needle traveling to the end of the record. So for a 12 inch, one revolution of the record at 33 1/3 rpm takes 1.8 seconds which results in a groove length of 36 inches (914 mm) at the most outer diameter. At the minimum allowable diameter the groove length is only 14.9 inches (378 mm) for the same 1.8 seconds. As a result the information within the groove is condensed to much less than half of its length compared to where it starts from. If you think about the river-example, the outer diameter represents the easy traveling part for our boat while the inner diameter of the record is the difficult part. Here the pick-up has to follow the same amount of groove-curvatures at less than half of the starting groove-length.

So how you can prevent these as a record producing person or vinyl-enthusiast?

Back in the days where vinyl was the main medium people where kind of familiar with the limitations of vinyl records. Records of that time usually have only ballads, instrumentals or some sort of smooth songs as the last tracks of the respective side. So maybe its worth to think about a different track-listing for cd and vinyl. Beside that you should avoid extensive highs in your mixes for vinyl if not artistically necessary. Try to get a balanced mix.

At the playback side there are basically two things about it. First a decent turntable with a reasonable pick-up. Both should suit your daily needs. These will be fairly different, depending if you’re a DJ or a vinyl-enthusiast. The other is the adjustment of your turntable like the right placement of your pick-upor the settings for the tracking-force and antiskating.
But that’s a topic for one of the next articles.
 

Seriously digging the grooves: Andreas [LUPO] Lubich is mastering-engineer and is co-owner of Dubplates & Mastering Under his moniker Loop_O he’s cutting vinyl-masterlacquer discs since 1999. He answers your technical questions and what you always wanted to know about producing good vinyl records.

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