A Dictionary of Music and Musicians/Analysis of Compound Musical Sounds
ANALYSIS of Compound Musical Sounds. The separation of such sounds into their component elements, or the determination of the elements they contain. The sounds ordinarily met with in music are not simple and single notes as is commonly supposed, but are usually compounds of several sounds, namely one fundamental one (generally the most powerful) accompanied by higher harmonics, varying in number and strength in different cases. These however blend so completely into one sound that the unaided ear, unless specially trained, fails to distinguish the separate elements of which it is made up. Such a compound sound is intentionally produced artificially with the compound stops of a large organ, and if these are well in tune and well proportioned, it is often difficult to distinguish them separately.
In acoustical investigations it is very desirable to ascertain of what simple sounds a compound one is composed, and this is done by a species of analysis similar to that so common in chemistry. In compound chemical substances the elements are, like the elements of a compound sound, usually undistinguishable by the eye, and the plan is adopted of applying to the substance a test, which having a peculiar affinity for some particular element, will make known its presence in the compound. Such a test exists for elemental Bounds in what the Germans call Mittönen; or sympathetic resonance.
Certain bodies will vibrate when certain notes, corresponding to their vibratory capacity, and those only, are sounding near them, and they therefore test the presence of such notes, whether perceptible or not to the ear. For example, if we wish to find out whether the note is present in a compound sound, we have only to bring within its range a sonorous body, tuned to that note, as for example the second string of a violin, and if that note is present, in sufficient force, the string will be sympathetically set in vibration. We can judge a priori by the theoretical laws of harmonics, what notes are or are not likely to be present in a certain compound sound, and by applying tests for each, in this way, the sound may be completely analysed, both (as chemists say) quantitatively and qualitatively, that is, we may not only find what notes are present but also, by proper provision in the test body, what are the relative strengths of each note.
This method of analysis is chiefly due to Hahmholtz, the test bodies preferred by him being hollow glass vessels. Each of these has such a capacity that the air it contains will vibrate with a particular note, and by having several of these, tuned to the notes required, the presence of these notes in any compound sound may be ascertained with great facility.