# Classical uncertainty principle

What assumptions underlie the classical uncertainty principle? The principle doesn't seem to apply when I want to know the precise pitch of a tone from a bowed violin string, since I can measure the duration (as precisely as I want) of the beats produced when I interfere it with a sine wave of known frequency. The violin string is fairly simple oscillator, not a completely unknown signal, and its frequency should be constant and stable. So, does the uncertainty principle apply only when you don't know the nature of the tone you're trying to determine the pitch of?

phinds
Gold Member
What assumptions underlie the classical uncertainty principle? The principle doesn't seem to apply when I want to know the precise pitch of a tone from a bowed violin string, since I can measure the duration (as precisely as I want) of the beats produced when I interfere it with a sine wave of known frequency. The violin string is fairly simple oscillator, not a completely unknown signal, and its frequency should be constant and stable. So, does the uncertainty principle apply only when you don't know the nature of the tone you're trying to determine the pitch of?
The uncertainty principle has nothing to do with violin strings, as far as I know, partly because they are macro-sized objects and everything averages out. The HUP is about micro-level things (electrons, etc) taken individually.

f95toli
Gold Member
The uncertainty principle has nothing to do with violin strings, as far as I know, partly because they are macro-sized objects and everything averages out. The HUP is about micro-level things (electrons, etc) taken individually.

The OP is referring to the classical (AKA mathematical) UP which basically is a consequence of how the Fourier transform (and our definition of frequency) work.
In this context all it means is that if you want to measure the pitch of the string with a good accuracy you need to measure for a long time and vice versa.

phinds