Comment by muffles

The harmonics of a guitar or piano can extend well beyond 8kHz, even though they contain lower frequency components that give them their characteristic sound. In fact, the higher harmonics can contribute to the richness and complexity of the overall sound, even if they're not heard as distinct pitches. Similar effect occurs with cymbals, the high-frequency shimmer of cymbals can extend well above 8kHz. Also violins can include overtones that extend beyond 8kHz and the sound of a trumpet can include overtones that extend up to 10kHz or higher.