And timbre is itself technically defined as all the aspects of a sound that are not pitch, loudness, or location. So, it doesn't really explain anything. It's

And timbre is itself technically defined as all the aspects of a sound that are not pitch, loudness, or location. So, it doesn't really explain anything. It's kinda circular. Timbre is itself the word for "sounding different" (without being different in pitch, loudness, or location). My simple answer: "different frequency spectrum + consistent patterns of change over time in spectrum, loudness, and/or pitch" E.g. it's not the loudness of trumpet vs piano, but it is partly the fact that trumpet doesn't consistently have the loud to quiet fade timbrel temporal pattern of piano