We define timbre as a set of auditory attributes—in addition to those of pitch, loudness, duration, and spatial position—that both carry musical qualities, and collectively contribute to sound source recognition and identification. Timbral properties can arise from an event produced by a single sound source, whether acoustic or electroacoustic, but they can also arise from events produced by several sound sources that are perceptually fused or blended into a single auditory image. Timbre is thus a perceptual property of a specific fused auditory event.