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Mar 06, 2018, 09:06 PM
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Shepard Tone Variometer Discussion Thread


The March 2018 issue of Radio Controlled Soaring Digest begins with an article titled "An Innovative Method for Acoustically Rendering Climb Data for Model Gliders Using Shepard Tones", by Helmut Stettmaier, in Bavaria, Germany. Here's a direct link to the March 2018 issue in pdf format.

In my opinion it's a very interesting idea. In fact, I've already implemented a version of it for OpenTX and tried it in flight, and it works! I've also been corresponding with Helmut Stettmaier.

In short, it's not actually a variometer, nor does Helmut call it that, it's really an audible altitude indicator. In my OpenTX version a tone sounds repeatedly with a pitch corresponding to my glider's altitude. If my glider goes up, the pitch goes up. If my glider goes down, the pitch goes down. If I'm circling in and out of lift, so that I'm alternating between rising and sinking, this system helps me determine if I'm achieving a net gain or net loss of altitude by comparing the highest pitches at the top of each circle. That's something an ordinary variometer doesn't do.

And if you're wondering how a tone can indicate your altitude over the wide range that sailplanes typically reach, without going beyond the frequency range of your ears, that's where the Shepard tones come in. I won't try to explain them here. Instead read about them on Wikipedia or do a YouTube search.

From the limited amount of testing I've done so far, my impression is that it'll turn out to be very useful. I currently have it on a switch along with my conventional variometer so that I can switch between the two. I envision cases where the conventional vario works better and cases where the Shepard Tone vario works better.

I'm still refining my OpenTX setup and it's not ready for release yet, but I'd like to get an idea about whether there would be much interest in Helmut's idea, either in the form of a hardware device, which Helmut is considering building, or in my OpenTX implementation. I'd also like to hear from anyone using FrSky gear who's interested in beta testing my setup when it's ready.
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