The Magic Chord is "C major"

I’m playing at the Indy Grand Casino today. So, for four hours, I will hear a constant drone of C major in my ears. Why? Because, it seems, all the slot machines today are tuned to the key of C. Now, I assume that casinos are sound designed to keep their investors(suckers) investing and popping credits into machines. But, I haven’t read that much on the psychoacoustics of the C chord, so I’m not really sure. It could be that that’s the easiest industry standard chord to pick. Imagine the cacophony of each machine manufacturer picking tones completely dissonant to the machine next to it. Also, keep in mind that there was a transition to the modern machine, so maybe it’s just a legacy sound so that it didn’t sound completely different from other machines.(Here’s a webpage that mentions that.)   

Music theory-wise, most of the machines play a 5th(C G) or octave (C C) and only when there is a payout do you hear the third(E) creep in. So, maybe, the third of the C chord or “E” is the most heavenly note in the western tonal system? Certainly, most guitar players would agree with that. It could be that a major tonality in any key is just soothing, which there certainly is enough proof of. I’ve often thought that on gigs that are more tip-dependent that I should play only major, happy tunes. But, then I realized, the result of this would be my unavoidable suicide or possibly the murder of an innocent bystander.

WIRED.COM has a blurb here on the design of the modern slot machine, noting that the machine is tuned to “C”. I don't know how many machines this casino has, but it's a lot of them. I’ll be playing in the middle of one for four hours. Maybe, I’ll try playing songs in dissonant keys like F#, B, or D# major. Security will probably want to have a word with me.

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