She smiled, grateful that Alex didn't know he was out of tune.
If, the two pipes are slightly out of tune when sounded separately together they sound a common note which may be higher than that due to either alone.
The more, therefore, these are out of tune the more rapidly will the beats follow each other.
The vibrograph is also well suited for the same purpose, and so in an especial manner is Helmholtz's double siren, in which, by continually turning round the upper box, a note is produced by it more or less out of tune with the note formed by the lower chest, according as the handle is moved more or less rapidly, and most audible beats ensue.
When any bell is out of tune it sounds mournful instead of joyous.