The human ear and examples of natural heterodynes

greysky · 2008-01-03T06:36:29+00:00

One night I fell asleep while watching the late movie and when I woke up, the channel had gone off the air, and there was the usual pattern of circles on the tv, along with a rather annoying steady tone. Curious to see how close I could whistle and perhaps match the tone from the TV, I noticed a quite clear heterodyne tone produced in my ears. The third tone would start out low (or was it high, I can't quite remember because this was 25 years ago) and would increase in frequency the closer I got to the center frequency. The next day I asked my physics professor about the human ear's ability to produce a heterodyne in this manner, and he stated flat out that it was impossible. Now, I wasn't gonna argue with the guy because finals were going to start and he held my grade in his hands and he was a bit of a hothead.... but I couldn't figure out why he thought it wsa impossible. Since then I've asked around a few more times, butthe general idea ws that the human ear could not produce a heterodyne signal - yet I quite clearly remember how easily my ears created one. Now, 25+ years later, my ears are not as good as they one were - tinnitus, some frequency selective deafness, and general ageism have taken their toll and I can no longer produce the heterodyne signal. So does anyone have any theories as to whether the human ear can produce a heterodyne signal? If you are a young'un I innvite you to do this experiment for yourself. All you need is a steady tone and the ability to whistle. Use a tone generator set to about 1.5 Kilocycles coming from a single speaker 3 - 5 meters away. Begin to whistle and slowly try to match the tone generator and then go a bit higher and lower. You should clearly be able to hear a third tone -the beat frequency- varying as the inverse of your whistled tone. Give it a try and tell us your results...Greysky

Jan 03, 2008 61 Replies

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Androcles 18 years ago

| >| >"John Larkin" wrote in | >message | >| >news: snipped-for-privacy@4ax.com... | >| >| On Fri, 04 Jan 2008 16:47:46 GMT, "Androcles" | >| >| wrote: | >| >| | >| >| | >| >| | >| >| >erg: | >| >| > a centimeter-gram-second unit of work equal to the work done by a | >force | >| >of | >| >| >one dyne acting through a distance of one centimeter and equivalent to | >| >10^7 | >| >| >joule | >| >| >

| >| >| | >| >| No. | >| >

| >| >F*****ad. | >| >

| >| >

| >| | >| But you're the one who's always wrong. By a factor of 1e14 this time. | >| | >Even I can make the occasional typographic error converting | >superscript in this antiquated text-only drool bag known as Usenet. | >

formatting link

| >Well done for spotting it, I congratulate you. | >F*ck you, smart arse, for not pointing it out immediately. | >

| >

| | Well, you elected to correct my typing, so it's only fair that I | return the favor. | No. (BTW, if you were Peter Brown you'd have said "it's only fare") :-)

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Bob Cain 18 years ago

Well, it isn't a modulation of either tone by the other but it is a modulation of their average frequency by half the difference in their frequency. That particular modulation doesn't require multiplication other than that implied by the identity:

sin(w1)+sin(w2)=2*cos((w1-w2)/2)*sin((w1+w2)/2)

where w1 and w2 are two angular frequencies.

Bob

"Things should be described as simply as possible, but no simpler." A. Einstein

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