Musical illusion

Several years ago I heard a strange musical illusion. I think it was on Jean-Claude Elloy's album Shanti.
It sounded like the tone was constantly rising in pitch without stopping.
Now I know that it is called the Shepard tone which can even decrease in a similar way.

Is there any one who knows how to recreate this in a modular patch?

Here are two Youtube examples:

Shepard tones (also called Risset tones, after J-C. Risset, the INA/GRM composer who used this quite a bit) are sort of weird. It sounds like the tone is continuously going up or down, but that's not what's up at all. The spectrograph above gives a few clues, tho...

You can see a continuous pattern of up-swept pitches that overlap. But you'll notice that you can't actually see the origin of the pitches, and that the amplitude reduces the higher the pitch goes. That's part of the trickery. The other part is purely psychoacoustic, and relies on how we perceive sonic foregrounds via amplitude.

OK...let's build one of these things. Take several VCOs, for starters. Set each one to the same low pitch, and mix them all together. Send this to a bandpass VCF so we can limit the passband we're listening to...this eliminates the obvious "bottom limit" and "top limit" pitches.

Now, here's the voodoo part: each VCO also receives a modulation signal from...oh, let's say we'll use several AD EGs. Long linear attack, pretty much no decay. The attack has to keep going while the signal is within the VCF's passband, but it starts moving the VCO's pitch up before the signal enters the passband, and keeps going until it's gone past the top limit. So now, we've got several VCOs and several individual ADs sending them pitch-rise modulation. Then the key to this is a trigger sequencer. Each EG gets triggered in turn; if you have six VCO/EG combos, use six steps. As each EG receives a trigger pulse, it starts to raise the VCOs pitch through the passband, then out the top where the decay kicks the pitch back down. Technically, you could stop there, as that right there gives you the continuous sweep illusion. But if you want to really make this perfect, you then use the EG triggers to trigger a second EG and then a VCA on each VCO, so that the VCA is only open for the time needed for the sweep, eliminating the possibility of the bottom pitch drone from bleeding through or the very rapid downsweep of each VCO being reset to the initial pitch.

So what WE hear now is that continuously-rising tone, with tones entering at the bottom, vanishing at the top, and yet it doesn't move...or so we think!

Thank you very much for the explanation!
I do not have all the modules that seems to be needed but I will make a try with what I have.

Hi Rookie,

How are you and how is your modular going regarding that Shepard Tone?

When I read this post back on the 24th of August and especially after the explanation of Lugia (thank you very much Lugia), though I felt the idea is very interesting, I was too busy with other stuff and at that moment, for me, it was too complicated to look deeper into it.

Very coincidentally though that I received two days ago a module that was or better, that is a very interesting module. One of the most interesting matters is that I managed with this one particular module to create a Shepard Tone that I discovered quite unexpectedly, please check this out:

Is that what you mean? If yes, then suddenly I got a rather easy solution for you to create that tone, it's just a matter of getting one module :-) The above "demo track" goes in the beginning up and after a bit more than a half minute, it goes the other way around and goes down till I let it fade away.

Other than this one module I only used a mixer (Doepfer) and an Audio Interface (input/output by Intellijel). To give the sound a bit more "touch" I added a slightly bit of a reverb by using the Ventris Dual Reverb (using single Reverb only by the way) from Source Audio.

Let me know if this was what you were looking for and good luck with the Shepard Tone ;-) Kind regards, Garfield.

Hi Rookie,

Ha, ha, I am being a bit mean here :-) Wanted to wait a bit longer but it's 3 am here and I need to get some sleep before get to work tomorrow... so I was hoping I could drag the tension a bit longer but on the other hand catching some sleep is quite good too ;-)

So, the module in my previous post I was mentioning is the Make Noise - Telharmonic. Check out Make Noise's website regarding this module. There are two (how interesting!) manuals as download for this particular module (Telharmonic). The Telharmonic, fair enough and that one on its own is already a very interesting module and has lots of interesting functionalities however there is a kind of hidden mode or special mode, if one presses the "H-lock" button for more than 5 seconds then the Telharmonic changes into the Spiratone music synthesizer module, different functionality within the same module! Now that was a nice surprise when I read that in the manual :-)

So I did that and then it didn't took me long to discover that Shepard Tone is possible with this module. I discovered that already last night but then it was getting to late, so that's why I came up today with this.

I hope this is what you were looking for, have fun with it and kind regards, Garfield.

Edit: Removed typo.

EDITED Sep 4th 2020, 01:02

Your Shepard tone sounds good, both up and down.
Interesting that Telharmonic has that as an option. Have to put that module on my wish list.
I tried Lugias patch but I do not have enough EG/VCO combos and my Seq Switch could not (as I hoped) work as a trigger sequencer.
Then I tried a patch from a Youtube video that seemed to be easier. Only 2 VCO, 2 LFO and 3 VCA. But with limited success.

But I will continue to struggle with theese two patches.
A Shepard tone would be a perfect backdrop for an ambient piece I’m working with.

Hi Rookie,

That ambient piece you are working on sounds interesting. I hope once it is finished that you will share that here with us? :-)

Good luck with your ambient piece and kind regards, Garfield.