Why do equivalent notes played on different instruments sound different?

Question

So if an A is 440hz, why does a piano playing an A sound different than a violin, a guitar, or someone’s voice making that same A 440 note? It’s obvious that the pitch is the same on each instrument but each instrument has a distinct sound. I’ve never heard an A on a piano and thought, is that a piano or a cello. Why can we distinguish between instruments?

In: 151

Answer 1

It’s physics. Sound is developed by a resonance of an object, or system. A violin resonates along its strings and through its wooden form. A piano similarly resonates along its strings and wooden and metal soundboards. The length and tension of the strings affects the sound, as well as the shape and size of the sound board or body of the instrument.

Any sound can be described as a combination (or sum) of many different pitches (or notes), each with different volumes. We can artificially create a note that is A440 with a sine wave that only requires one pitch to describe (a sine wave at 440 Hz), but most tones aren’t that artificially simple. A440 on a violin is actually described by an infinite number of pitches all resonating together (just that the vast majority of those pitches are imperceptible). We hear it as 440Hz because that is the loudest pitch of them all, but also because the next loudest pitches in that tone are all *harmonics* of 440Hz, which means they reinforce the fundamental (generally the lowest pitch in the harmonic content).

There is also an envelope which affects the sound quality of an instrument. The easiest way to think of this is how you make word sounds with your mouth. Just go “oo-ah-oo-ah” out loud. It’s the same fundamental pitch, but the tone changes depending on the shape of your mouth. The shape of your mouth acts like a filter which dampens or augments certain harmonics of the note you are singing. The shape of an instrument has a similar effect.

The timbre, or sound quality of an instrument is created by the unique harmonic content, as well as its envelope and how that envelope interacts with the harmonic content.