The Korf Blog

The inside story: our research,
development and opinions

30 November 2021
Acetate Disc Longevity
First of all, a great big "Thank you!" to everyone who made a preorder of the new Korf Tonearm. If you did, you should have a preorder confirmation in your inbox by now. Please write me if you haven't received one. If you didn't preorder, the next opportunity to do so will be in Q2 2022, once the first batch is shipped.

Our friends and partners at The Supersense have also released something revolutionary — amazing music from the Universal archive, cut directly on acetate lacquer. They were issuing direct cut lacquers before, but this is the first time they could do their magic with the tapes from a major label.

This limited series created a lot of excitement and a bit of a controversy. Some experts jumped at an opportunity to point out that these directly cut acetate discs are incredibly fragile and are only good for a few plays. How do they know? Apparently, it's "common knowledge".

Shall we look a bit closer at this "common knowledge"?
Conflict of Interest Statement: the owners of Korf Audio are a minority shareholder in The Supersense. Operationally, Korf Audio and The Supersense are completely separate. None of Korf Audio employees hold any positions at The Supersense and vice versa. Korf Audio conducted the research below on its own volition and is not compensated by The Supersense for it in any way.

The Hows and the Whats
How can we judge the longevity of analogue media? We hear the dropouts on a tape, the pops and clicks on the LP. We know that if we play an LP with a bad stylus, we'll ruin it irreversibly. Same for tapes and magnetized heads.

But what about the gradual degradation? What happens between the first play and the 10th? The 10th and the 50th? After the hundredth playback? How can we objectively estimate the damage?

As you probably know by now, spectral analysis is often our tool of choice. And, very conveniently, any analogue degradation will show in the accumulated spectrum of the recording.
As you probably know by now, spectral analysis is our tool of choice
More hiss? You will see it in the spectrum. Clicks and pops? You will see them in the spectrum, loading up the higher frequencies. Distortion? Yes, you will see the difference in the spectrum between the distorted and the original version.

In fact, I cannot think of a kind of analogue degradation that will not leave its trace in the accumulated spectrum of the signal. If you can, please share it with me!
Our plan becomes clear. We will record to file the first ever playback of the acetate, then (approximately) 10th, 50th and 100th. We will then do an accumulated spectral trace of the same passage on all the playback files. Comparing these spectral traces, any degradation will be highlighted as a difference in spectra.

For the recordings, we will be using our Micro Seiki RX-1500, a prototype Korf Audio tonearm with an HS-A02 headshell, and an Audio Technica AT7V cartridge that I very much like for being neutral, perfectly linear into 47kOhm/200pF load, and yet musical. For amplification, a simple discrete FET phonostage will do. It's on the level of today's good budget phonostages. If you want to know more about it, googling "Otto Aikido 1" will get you there. We chose it for its known gain stability. Its output is fed into Steinberg UR22 audio interface.
To go through dozens of playbacks, we will use a linear tracking turntable with a "repeat" function. Hitachi HT-L303 will never be an audiophile icon, but will serve our purpose just fine.

I will open a brand new P-mount Audio Technica SS335E/U cartridge especially for this exercise. It should provide typical wear expected from a quality cartridge. If anything, I am a bit wary that it might mistrack at its low 1.25g downforce. The cut we'll be using is quite "hot".

One last note: this isn't some specially cut test acetate. No, this is The Supersense's Mastercut acetate, taken off their production line. John Coltrane's "Love Supreme". I am not interested in theoretical performance of test signals on lacquer. What I want to know is how well actual music will hold on after a hundred plays.

The Measurements
Here is giddy excitement of the first 10 playbacks of Side 1, speeded up to take a bit less than the actual 2 hours and 50 minutes. We have videos of the first fifty playbacks, but thought that watching them all is just too rousing!

I was a bit surprised at how long it took. 40 additional plays lasted for 11 hours 20 minutes, and then 50 more plays took another 14 hours. A hundred playbacks is a lot.
We have, of course, recorded the first ever playback of the lacquer to establish the baseline. It's referred to as Play 0. Then we have added 11 playbacks and recorded the 12th. Then another 39 playbacks, recording the 51st. And then there was a monster session of 52 playbacks, with 103rd being recorded. I know round numbers would have been prettier, but we have decided to never stop the started playback. If the needle hits the lacquer, the whole side is played.

We took the resulting 96/24 bit files, trimmed them to 1/10th of a second precision, and did an accumulated spectrum of the 1 minute 30 second clips starting 1 minute into Side A. Hanning windowing is applied, window size is 4096.

Let's see what the difference is in accumulated spectral traces between Play 0 and 12. Drag the red line left and right to explore:
What, there's none? Yep, there is no difference, at least none that we can see without zooming very far in.

Maybe there's something between Play 0 and Play 51?
No visible difference again. But with more than 100 playbacks, there's bound to be something! This is supposedly incredibly fragile acetate lacquer, remember? So what's the difference between Play 0 and Play 103?
The "incredibly fragile acetate lacquer" plays back the hundredth time exactly as it did the very first time.

For the reference, here are all the playbacks in one chart. The lines are made semi-transparent to make all the spectral traces visible. The traces are so similar that they exactly overlap each other with uncanny precision.
All right, but there must be some difference. Let's zoom in really deep and look at just the differences between the first playback and all the others:
The maximal divergence of the spectral traces is paltry 0.8 decibel at 20 kHz. I've seen larger differences in recorded files just because the preamp's capacitors warmed up.

The spectral trace for 103rd playback is closer to the first and the 12th than the 51st. I believe the extra HF "peak" on the 51st recording has more to do with some electrical fluctuations than with the groove wear.

Acetates as Consumer Media?
The Mastercut lacquer is a genuine alternative to owning a master tape copy
I have expected to see more difference between the first and the hundreds playback. A few years ago, we did a similar experiment with an Apollo-made lacquer. There was a couple of dB of high frequency degradation after a few dozen playbacks. The less than 1 dB divergence we saw here is really within the measurement margin of error. It looks like the Japanese MDC acetates The Supersense uses are much better made.

Our today's test shows that the Supersense Mastercut acetates work surprisingly well as a consumer media. A two track magnetic tape will lose a lot more information after 100 playbacks. The Mastercut lacquer is a genuine long lasting alternative to owning a master tape copy.

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