Sunday, February 06, 2011

Shepard Tone

A few years ago, I was enjoying a meal at Luxor in Las Vegas and the music surrounding me was someone playing a scale that seemed to ascend forever. It continually went higher in pitch. Obviously that was impossible, but that's how it sounded. It was a slow, stately ascent as though someone was ascending Escher's stairs. It wasn't annoying ( I was eating dinner), and it wasn't background music. It was demanding music, but every time I thought it would become transcendent, something happened and I found myself listening to it climb the ladder again.

Yesterday I learned that this wasn't a clever invention of Luxor, but a known phenomenon. There's a way to balance the ascending scale with the loudness of the tone and the loudness of its octave below to fool the ear into thinking the scale is always ascending. It's called the Shepard Tone, and here's an example of it rising, although nowhere near as stately as the one I heard in Vegas. And here's an example of it falling.

As you can imagine, the Las Vegas scale was beautifully worked out, not continuous but resembling that of a keyboard instrument, and it had me captured for an hour. These web versions aren't as hypnotizing, but man, what an illusion. I'm used to optical illusion, but that was the first aural illusion I had. The mp3s I link to aren't nearly as captivating as the real thing in the wild, but I couldn't find the genuine article out there.


Mike said...

I remember hearing a similar effect in my youth at the end of Echoes or Return of the Son of Nothing (oh, yes!) AKA Side 2 of Pink Floyd's Meddle.
Here it is coming in at about 22 minutes with the birth of the Star Child. Drop that tab!
(After a bit of fact checking, I'm told that it's a Shepard-Risset choral glissando.)

KaliDurga said...

That is a fascinating phenomenon, but I think that listening to it for more than a minute would drive me insane.

Peromyscus said...

Yes, the Risset scale is the continuous one. I'd never listened to Echoes with that in mind, so thanks for bringing it up.

I love Echoes.


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