Why does, say, a note on a violin have a “pitch”, but the sound made when I bang a table doesn’t have a “pitch”.
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When the sound energy is concentrated into one or more frequencies, it’s perceived as having pitch, or we can say it’s *tonal*.
When the sound energy is broadly distributed across a wide range of frequencies, it’s perceived as noise. Different distributions get different names (white noise, pink noise, etc). A balloon popping is an example of noise.
You can selectively filter noise, and in the process you can give it a tonal quality. If you make a shhhhh noise and shift your lips from an ‘o’ shape to an ‘e’ shape you’ll shift the frequency distribution and give the sensation that while they’re both noise, one seems to have a higher pitch.
A drum head produces a wide range of frequencies (noise) but also has some *standing waves* which have particular frequencies so it can be tonal. Some drums are more noise and less tone, whioe other drums (eg tympani) are more tone and less noise.
When you draw a bow across that violin string, you’re dragging the string out of position and its returning force makes it slip back from the bow, many times pwr second. How many times that happens per second is a function of that returning force and the weight of the string; that number of times per second dictates the fundamental pitch of the sound.
When you bang a table, every little bit of it is displaced and experiences a returning force. Its irregular shape and irregular density means that the wobbles which are set up in all the different parts of the desk have many, many different frequencies. It’s not tonal, and you hear it as noise.
^(edit: added the bits about the violin and desk which OP asked about)
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