Warning: this is a bit geeky...
I've always had a good ear for tones-- I can go several years without hearing a song and sing it in pitch. If I would train my ear better, I guess I could say I have perfect pitch.
So I've always had this idea of listening to a 440Hz A tone on a regular basis to train my ear. I realize some people like to use a slightly different frequency for A-- no argument from me, this is just the tone I get off of my pitch fork. This actually works pretty well-- I can hit a 440Hz A pretty consistently.
I had this idea of generating a reasonably long 440Hz tune as a sound file, loading it into my MP3 player, and listening to it for long periods of time. A perfect time for this would be while I was running-- I'm a captive audience at that point, and running always puts me in a kind of meditative mood anyway.
So I needed to generate a 440Hz A sound file. I found a command to do that on a Linux machine:
sox -w -s -t .nul /dev/zero 440.wav synth 300 sine create 440
This creates a 51MB file, so I guess you could actually just make it a minute by replacing the 300 with a 60. It's just that there is an annoying skip every time the MP3 player loops back around to play again, and I wanted to minimize that.
I created the .wav file, then transferred it to my MP3. I was all set.
I took off running from my office in Center City in Philadelphia. I didn't take a particular route, because I did the bridge yesterday-- besides, I just like running around Philadelphia and learning the streets. I turned on the MP3 player and put it on a constant loop with my new 440Hz sound.
The first thing I noticed was that it put me into a very weird place, mentally. I normally have a lot of mental chatter (this must be what "hearing voices" means)-- I try to shut it off, usually unsuccessfully. The tone kind of blocked that out. The second thing I noticed was that my perception of this constant frequency, constant amplitude sound varied a lot. I can actually "perceive" it as higher or lower. The file is a simple sine signal.
Finally, one very unexpected effect was that, without the monkeys chattering up there, I ran faster! How very odd. I was able to concentrate on my form (I learned my running form out from a book called ChiRunning by Danny Dreyer), up my cadence, keep my posture erect, and strike mid-foot, not on my heel. Nothing hurt, and I had a sensation of running fairly effortlessly. Nice.