Although plucking a string on a guitar and hitting a string on a piano can produce the same fundamental frequency (the perceived pitch), the resulting sound can still sound quite different due to several factors:
Tone Generation: Each instrument has its unique method of tone production. Guitars produce sound through plucking or strumming vibrating strings, while pianos produce sound through the striking of strings with hammers. The distinct mechanisms of tone generation and the materials involved contribute to variations in timbre, attack, sustain, and decay of the sound.
Harmonic Content: When a musical instrument produces a sound, it often generates not only the fundamental frequency but also harmonics—higher-frequency components that give each instrument its characteristic timbre. The relative strength and distribution of these harmonics vary between instruments, resulting in differences in the overall sound.
Resonance and Body: Instruments possess resonant bodies or structures that influence the sound. Guitars have a hollow body that resonates and amplifies the vibrations of the strings, while pianos have a complex structure of strings, soundboard, and wooden frame. These resonant properties affect the timbre and richness of the sound.
Playing Technique: The way an instrument is played also affects the resulting sound. Factors such as the force applied, the location of the string or key that is struck, the use of different playing techniques (e.g., bending a guitar string, using the sustain pedal on a piano), and the nuances in articulation contribute to the variations in sound.
Therefore, even when playing the same note on similar instruments, the inherent characteristics, construction, and playing techniques of each instrument result in distinct sounds, making them sound different from each other.