What should frequency estimation functions do for non-tone signals?

[endolith]

In #19 it was pointed out that the frequency estimation functions fail for a silent input. This isn't something they were meant to handle, but how should they handle invalid input like this?

Other signals like noise, music, DC values, etc. would either produce no result, or an invalid result, too.

The functions could be modified to have a threshold of confidence that they found the right value, so that a white noise signal would fail, for instance, instead of producing an arbitrary value.

(Originally these were just examples of the frequency estimation algorithms and not meant to be used in production, but this library is for production purposes now, I guess.)

[endolith]

I wish this supported Approval Voting...