Shepherd Tone

This week I want to talk about something called the "Shepherd Tone" have a listen below:

Interesting right? It was brought into the foreground of my attention recently when I listened to a GDC (Game Developers Conference) by Mick Gordon on the sound work he did for the newest Doom game. Mick's an Australian composer and sound designer who works freelance for AA to AAA game titles, great guy and very talented. His talk was mostly about the music but a question from an audience member about a particular sound effect brought up the shepherd tone.

The shepherd tone is essentially a series of tones separated by even octaves. As the tones ascend or descend, the amplitude is altered, with the higher octave getting quieter and the lower octave getting louder until the scales end and restart. The fading of the amplitudes at the right positions is what creates the endless effect.

Neato!

So why do I care? Well....

Aside from the fact that audio illusions are really cool, the application of this idea is very evident in the world of video game composition and sound design. I didn't realize what was happening at the time but back in 1996 or whenever I was playing Super Mario 64, I was exposed to the Shepherd Tone as a maniacal musical piece. In Super Mario 64 there is a room that is just a straight staircase, if you've collected enough Power Stars you'll have no trouble just climbing the stairs and reaching the door at the end. But if you haven't got enough stars, you can never get to the top of the stairs, they just loop indefinitely. You can run up them for 10 hours like the video below but you can't reach the top. All the while your ears are treated to a Glockenspiel and String Ensemble that appear to be stuck forever climbing alongside you.

Absolute Magic!

Now the musical applications of the Shepherd Tone are fairly obvious, however what I hadn't considered until hearing Mick Gordon explain it himself was the Sound Design applications. To be honest I probably wouldn't have noticed this as a Shepherd tone but in the clip below, I've isolated a moment that puts this idea into context, although I'm sure there are plenty more in this hour long video:

If you missed it here's what's happening.

When the player wounds an enemy they can walk up and perform an overly graphic glory kill if they need to satisfy some strange urges they might have inside. When this happens the game goes slow-motion and the background music is briefly ducked out to make room for a siren like sound effect. This sound effect is a Shepherd tone, it can go on forever and it will perpetually build tension. Mick created this as a Shepherd tone because each glory kill is different and they all go for varying periods of time. To solve the problem of creating multiple sound effects he created one that could be used in all situations without the need for any extra processing power devoted to warping audio.

Pure Genius...

So wrapping up, I usually like to give vague future predictions of how I might apply this technique to future projects, but this time I have a project I'm working on right now that could benefit from some shepherddy goodness. More on that in my project wrap up blog, coming soon!

Until next time, thanks for reading!

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