§ 9. Timbre.—The same note sounded on a piano, a violin, a trumpet, etc., has a very varying character, though its pitch is identified as the same. Differences of this kind are called differences of timbre. Timbre is due to the complexity of the sensation. Ordinary musical sounds, even when they arise from a single source, are not simple. Attentive analysis can discern a number of distinct partial tones. The power of discrimination varies with musical aptitude and practice in analysis. The pitch of the whole complex is approximately the pitch of the lowest tone. This is called the fundamental tone and is of course identified at the outset. The overtones, as they are called, are separated from the fundamental tone by harmonic intervals. The most intense of them are usually those which have most affinity with the fundamental tones, such as the octave. Thus, though their relative intensity makes it easier to discriminate them, their harmonic relation makes it more difficult. With sufficient practice, a person of natural musical aptitude acquires great power of discriminating overtones. The less skilled may use artificial helps. Thus the partial tone may be first sounded separately on the key of a piano, and then kept in mind in attending to the note which is to be analysed. Several tones in succession may be tried in this way; some of them may be discernible as constituent overtones and others not. Sometimes slight differences in pitch are noted between the overtone and the corresponding note as sounded on the piano. This is one of the reasons why the analysis must be regarded as real, and not illusory.
A moderate number of relatively low partial tones makes the whole richer and fuller and somewhat higher in pitch. A large number of high overtones of considerable intensity gives to the whole a sharp and penetrating and sometimes a somewhat harsh character. The harshness arises from beats between the high overtones.
The combination of partial tones in a complex note produced from a single source is analogous to the combination of notes from different sources, except as regards the great difference in intensity between the fundamental tones and the overtones. The whole experience due to the combination is specific in its character, and is not a mere summation of the experiences severally due to the partial tones. This is true even when the partial tones are discriminated. They are still apprehended as constituents of a whole having an unique character. Analytic attention in discovering overtones does not appear to create them in the moment of discovery, but to find what is already preexisting. Thus the composition of an ordinary musical note affords an excellent example of sensations which are merely felt without discrimination of their distinctive qualities. So long and so far as the experience is unanalysed, the constituent sensations are present, qua sensations, though their presence is not cognised. There is a sensedifferentiation without perceptual distinction.