The American National Standards Institute defines timbre as "...that attribute of auditory sensation in terms of which a listener can judge that two sounds similarly presented and having the same loudness and pitch are dissimilar". According to this definition, timbre is the subjective correlate of all those sound properties that do not directly influence pitch or loudness. These properties include the sound's spectral power distribution, its temporal envelope (as would be shown on an oscilloscope display) and depth of amplitude or frequency modulation, and the degree of inharmonicity of its partials. The timbre of a sound therefore depends on many physical variables. It has been shown that from a subjective point of view the sensation of timbre has about three rather orthogonal dimensions. These can be represented by the verbal ranges dull-sharp, compact-scattered and colorful-colorless. These subjective dimensions are loosely related to the physical quantities of high-frequency energy in the attack, synchronicity in high-harmonic transients, and spectral power distribution.
The concept of timbre plays a very important role in the orchestration of traditional music and in the composition of computer music. There is, however, no satisfying comprehensive theory of timbre perception. Neither is there a uniform nomenclature to designate or classify timbres. This poses considerable problems in communicating or teaching the skills of orchestration and computer score writing to student-composers.
In the following demonstrations one can hear how spectral make-up, temporal envelope and degree of spectral inharmonicity all have a very specific influence on the perceived timbre of sounds from musical instruments.