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”.
In: 1
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)
Something that has a pitch is just any sound that repeats at some frequency.
When you pluck an “A” guitar string, it vibrates 440 times per second, which creates pressure waves of air that repeat 440 times per second too. That’s its pitch.
When you bow an “A” violin string, it also vibrates 440 times per second. The type of vibration and the way the pressure waves reverberate through the instrument are really different, so the shape of the sound itself (the “timbre”) is really different, but just like the guitar string, the sound repeats itself every 1/440 of a second.
When you sing, your vocal cords are vibrating a certain number of times per second too. The shape of your mouth affects what it sounds like, but the frequency – the pitch – is just based on that fundamental vibration.
When you bang on a really solid table or clap your hands, the sound is more instantaneous – it doesn’t vibrate, so you’re just hearing the instantaneous pressure wave of air rushing away as you strike something and the air between your hand and the object moves out of the way. If there’s no periodic vibration, there’s no pitch.
When you hit an object that vibrates, though – even a little bit – it does make a pitch, but sometimes it’s too low or too high for us to perceive it that way. If you record the sound and the speed it up or slow it down, you can hear the pitch, like in this video:
All sounds most definitely make sound waves at a variety of frequencies. For it to be “musical” I suppose it would have to consist of a fundamental frequency and additional frequencies that are harmonics of that fundamental.
Although, a lot of percussion would evade that strict definition. So maybe I’m just full of crap?
Latest Answers