Sound in physics

Clanket

Hi all. We're doing a project in College (Computer Science) and we've decided to do it on sound. I'm having a bit of hassle trying to get my head around what exactly makes one sound different from another. Can anyone confirm that a sound is made up of the followinhg: -

1. Intensity / Amplitude
2. Pitch / Frequency
3. Tone & Harmonics

Can you have a sound from two different instruments with the same Amplitude and Pitch. If you can but they sound different, does this mean it is only the Tone & Harmonics that distinguish sounds?

Also, does anyone know of any good interactive websites. I've looked at thephysicsteacher.ie, physicsclassrom.com and teachersdomain.of. Anyone any other suggestions?

Thanks for any help.

lumo22

timbre, just google it!

firefly08

I don't know if any of this will help, but what the hell, here's everything I know about this:

Can anyone confirm that a sound is made up of the followinhg: -

1. Intensity / Amplitude
2. Pitch / Frequency
3. Tone & Harmonics

That's right. "tone" in the sense you're using the word refers the harmonic content, specifically the relative amplitudes of the various harmonics. Not to be confused with the musical term "tone" which refers to a pitch interval (equal to 2 frets on a guitar).

Can you have a sound from two different instruments with the same Amplitude and Pitch. If you can but they sound different, does this mean it is only the Tone & Harmonics that distinguish sounds?

Well yes many instruments overlap in terms of the base frequencies of the notes they can play (but also, many don't). What distinguishes them is harmonic content and also the way the 3 components in your list vary over time; for instance, a piano note typically has a fast attack and decay (i.e. it starts and stops suddenly) whereas a violin can "swell" in and out, i.e. it can have slower attack and decay. But this is not a new item for your list - it is simply amplitude and tone expressed with respect to time. (Note that the tone of all instruments changes with volume due to physical characteristics of the instrument.)

A "pure" sound is one with no harmonic content - this is a sine wave. So if you had an instrument that makes a sine wave, only the amplitude and frequency determine what it will sound like; another instrument that can produce the same frequency and amplitude will sound identical.

All sounds, and indeed all waves whether audible or not, are simply combinations of sine waves at various frequencies. If you were to take a sine wave at a base frequency, let's say 1khz, and combine it with another one at 2khz, but with lower amplitude, and then another at 3khz, at a lower amplitude still, and so on, ad infinitum, you'd have a square wave. The square wave would sound fuzzy (like distorted guitar) whereas the sine wave alone would sound kind of chimey (sorry I know that's not really a word).

Clanket

That's a big help, thanks a million.