Q: Why do guitar and piano sound different even while playing the same note?

A: The “quality” of sound, also known as timbre, refers to the unique characteristics that distinguish one sound from another, even when they have the same pitch and loudness. Timbre is determined by the harmonic content, or the relative levels of different frequency components, of a sound. For example, the timbre of a guitar and a piano playing the same note will be different because the harmonic content of the two instruments is unique. Timbre is also affected by the way a sound is produced, such as the materials used to make the instrument and the technique of the player.