|What accounts for the difference between two sounds having the same frequency, loudness, etc. but generated by a guitar and a sitar? — AW, Karachi, Pakistan
Different instruments sound different, even when they play the same notes at the same volumes, primarily because they add different amounts of harmonic tones to their fundamental tones and because these various tones change in volume with time. When you play a note on a guitar, you don't hear just one pure frequency with a constant volume. Instead, you hear the fundamental frequency and all of the integer multiples of that frequency—the harmonics of that frequency. The relative volumes of those harmonics, and how those volumes change with time, are characteristic of the guitar. If you listen to the same note on a sitar, the relative volumes of the harmonics will be different and you will hear the difference. Because both instruments are plucked, the sounds they emit both start loud and gradually grow softer. If you were to bow their strings, the sound would start soft and gradually grow louder. That's one reason that you can distinguish a guitar or sitar from a violin.