In this section
next PERCUSSION INSTRUMENTS.
PRELIMINARY.
A number of number instruments with different mechanical methods of tone-production and of widely varying musical effect must be grouped together under the heading "Percussion" or "Struck" Instruments. They all have this in common however, that, in playing them, the performer sets up vibrations by beating elastic and semi-elastic surfaces which are in contact with the air.
Gevaert subdivides these Percussion Instruments into
(1) Autophonic Instruments.
(2) Membrane Instruments.
In the former he says'" the tone is produced by the vibration of solid (metallic or wooden) bodies, of a nature sufficiently elastic to be capable of keeping up the vibratory motion imparted to them, usually by percussion." They include
(a) Instruments of definite pitch, such as Bells, Glockenspiel, and Celesta.
(b) Instruments of indefinite pitch, such as Triangle, Cymbals, Gong, Castanets, and so on.
The Membrane Instruments are, in a word, the Drums. They include
(a.) Instruments of definite pitch, such as the Kettle-Drums. (b) Instruments of indefinite pitch, such as the Side-Drum, Bass-Drum, Tenor-Drum, and Tambourine.
This subdivision of the "Percussion" into "Autophonic" and " Membrane " Instruments depends for its logic solely on the degree of elasticity in the struck surface. It seems to be based rather on musical than on scientific considerations. We shall therefore content ourselves by classing all the elastic and semi-elastic beaten surfaces together as " Percussion Instruments." However, a musical subdivision of the whole group must be made. This is not difficult. In some of these instruments the vibrations in the elastic material set up irregular vibrations in the air. These are the " Unmusical Percussion Instruments." Others set up regular vibrations. These are the "Musical Percussion Instruments." The former produce noise, but not sounds of definite musical pitch. The latter produce sounds of definite musical pitch.