Harmonics are the extra sounds above and below the main notes in music. Tibetan bowls and Mongolian throat-singers are famous for them. But you can also hear them in certain Tibetan chants (the really deep, growly ones), some other singing and musical instruments, and in certain kinds of drumming.
It is said that shamans actually travel on the overtones (harmonics of drumming) and I believe it. I can sometimes here overtones in rattling, too. And it sounds to me as though a form of throat-singing is how that characteristic sound is made in the didgeridu.
Our shamanism Meetup group sometimes practices harmonic toning---not often enough, I guess, but whenever we need to use it with an ecstatic trance posture. (For more info on ecstatic trance postures see Shamanista.com or my Houston Shamanism Examiner column.)
Last Saturday I taught how to do it again, because there were some new people present, and then I taught them a new trance posture to do the toning with. All I did was get them started in a couple of the simpler forms of hoomei, or Mongolian throat-singing.
It was one of those nights. The CD player would not work, so instead of getting to try out the posture with them, I had to drum. But I also needed to tone with them, because in a smallish group (nine of us), people tend to be shy about singing or making what are to them weird noises.
The problem was that toning tends to make my drumming slow down too much, and I was really tired already from drumming for a couple of other journeys.
So I started drumming, intending not to tone, but I did anyway, and it was amazing. I got more harmonics (the high whistling or fluting sound in throat-singing) than I probably ever have (since I never practice). And the drumming did not slow down.
Apparently I tranced out while toning. One of the other participants claimed that I drummed for 40 minutes, when I thought it was just 15 or 20 minutes. I knew harmonic toning was a great meditation, but I did not expect to trance out like that while doing it.
So here is my recommendation: Find a place to learn harmonic toning or throat-singing, and give it a try. If nothing else, get some good throat-singing CDs and harmonic toning CDs, like those of David Hykes and his Harmonic Choir, and listen to them carefully while in a quiet, meditative state.
Listening to harmonic sounds will make you feel great! And it is the first step in learning how to do it yourself.
Learning to make harmonic sounds yourself will make you feel even better.