The Beat that isn't -- or is it?

[Ric Brekne]

Kent:

The sine waves that I combined together to make the wave file I posted 
show no measureable overtones using Tunelabs Inharmonicity tool. Neither 
could Cybertuner pick anything up.  Now the phase display that Tunelab 
has showed a very intermittent response at around 880 for the 440 
signal.  This response faded in and out and its frequency wavered quite 
a bit. I doubt that this is an overtone per se. I fail to see how these 
non existing coincidents can account for the beat rate in the wave file. 
And so I question whether or not it is there. This echos Ed's and others 
ponderments and its a fair question. And  I dont see that  simple 
coincident partials theory provides an answer to it.

Every link I find that describes tuning forks describes them as 
instruments that have (for all practical purposes) no overtones.  Such 
as the below. Several sights which describe experiments like the one you 
did with your cybertuner attribute (sometimes) presence of very weak 
overtones that are not accounted for by the design of the tuning fork to 
sympathetic vibration from surrounding material... such as what ever you 
grounded your tuning fork on.  John Walker tuning forks make a real big 
point out of emphazising the <<overtone free>> characteristic of their 
tuning forks in all their advertising.   One other point. The duration 
and strength of your <<overtone>> is not sufficient to account for the 
long duration and intensity of the beating between the fork and the non 
coincident F3.

I say something doesnt add up. 

Cheers
RicB

http://hyperphysics.phy-astr.gsu.edu/Hbase/music/tunfor.html