St John Karp

Ramblings of an Ornamental Hermit

The Great Diamond Disc Experiment

I found it in the dumpster of a record store — what looked like a 78, but as thick as a dinner plate. When I took it home and tried to play it back, it sounded so muted and crackly I put it to one side as curiosity that I’d never get to hear. It was only months later that I realized what I had — an Edison Diamond Disc. These were a medium that competed with 78s until 1929 when the Edison Discs finally lost out. Instead of a lateral groove where the soundwave goes side-to-side, Edison Discs used an unusual vertical groove that played up-and-down. Even more strangely they played back at 80 RPM instead of the normal 78.

These days it’s hard enough to find a turntable that will spin at 78 RPM. How much more difficult is it to find one that spins at 80 RPM, not to mention a cartridge that plays vertical grooves? I thought these were nearly impossible to play back on modern equipment, and yet here’s mine in glorious MP3:

Download Reed Orchestra - A Summer Girl

Download Reed Orchestra - Whispering Flowers

How was this possible? In his YouTube video Edison Diamond Disc user Mark5W8Comer explains that you can play an Edison Disc back using a regular stereo cartridge. Because stereo cartridges are designed to pick up diagonal movement from the groove walls, it’s possible to play the record at 78 RPM, grab each channel of the stereo signal, invert one, and then combine them to enhance the peaks and troughs. This solution is, frankly, brilliant. We can listen to our Diamond Discs again! The only caveat is that you need a relatively sophisticated turntable that will allow you to reconfigure the cartridge outputs. Even then, you’re listening to the record slightly slower than intended. There is, I think, another approach that has the added benefits of letting you play the record at the correct 80 RPM and clean up some of the noise.

1. Digitize the Record

The first step is to digitize the record. Play it back on a stereo turntable and capture the output on your computer. I don’t know if it matters what your playback speed is, but I suspect 78 RPM is the best choice because slower speeds may cause the stylus to pick up more imperfections in the groove. Slow-playing grooves weren’t designed for the sensitivity of modern styli.

I played mine back at 78 RPM and recorded the output with Audacity. The rest of these instructions will assume you’re using Audacity too, but any reasonable editing software will do.

2. Speed it Up

Once you have the stereo recording, the next step is to speed it up to 80 RPM. Audacity has a “Change Speed” feature that speeds up the sound by percentages. We need a little basic maths to calculate 80 RPM as a percentage of your playback speed. The equation is this:

x = 80(playback) x 100

If your playback speed was 78 RPM, you need 8078 x 100 = 102.564102564. Thus, you need to speed up your recording by 2.564102564%. If you played back at 45 RPM, you need to speed it up by 77.777777778%. If you played back at 33 1/3 RPM, you need to speed it up by 140%.

Once you’ve done this, you will have a recording that plays back at the correct speed.

3. Split the Track

Now split your stereo track into two mono tracks. Audacity makes this easy with a “Split to Mono” feature in the menu to the left of your track.

4. Invert one Track

Select one of your mono tracks and invert it.

5. Recombine the Tracks

Mixdown the two mono tracks as one mono track. This will double the peaks and troughs to enhance the sound of the recording. If you listened to it before now you’d have noticed it was foggy and distant. It should be much clearer after this step, but it’s still kind of crap. There’s a lot of noise and crackle, but don’t worry, we can work on that.

6. Equalize the Hell out of That Crackle

I had to play around with it a lot, but I realized the crackle was largely high-pitched — higher than the sound of the music. I was able to filter out the worst of it using an equalizer that silenced the higher frequencies. This inevitably dulls some of the higher frequencies of the actual music, so experiment a bit and be careful you don’t remove too much of the sound.

7. Reduce the Noise

As a last bit of polish, you can reduce the noise on the recording. Select an area of pure noise from either before or after the music starts. Open up the “Noise Reduction” feature and use your selection as a sample. Then select the entire recording and reduce the noise. I find a light touch is best here, as too much noise reduction will make your music sound dull and muted, not to mention producing weird audio artifacts.

8. Amplify the Track

Now your tweaking is done, but silencing so much noise and crackle leaves your recording a bit quiet. Boost it by amplifying the volume so that the music is as loud as it can get without being clipped.

9. Gloat

YOU DID IT. You took a 100-year-old record, completely unplayable on modern equipment, and managed to hack it. The outcome is far from perfect, but it’s pretty good considering the age of the record and the lack of proper equipment. If you digitize your own Edison Discs, I’d love to hear the results.

With many thanks to YouTuber Mark5W8Comer for showing us how it’s done.