• Sound and air stream

• Properties of sound
• Tone production

Tone production

Two fundamental elements which are necessary for tone production can be found in every musical instrument: the vibrator and the exciter (the source of energy).

In musical instruments we can find a great variety of vibrating bodies, which differ in size, shape, material, mass and elasticity. The properties of these vibrators determine the characteristic frequencies (the pitch) and to an extent the timbre. The resonator (the body of the instrument) has an influence on the timbre and in some instruments on the fundamental frequency as well.

To start and keep the vibrations going, a source of energy (excitation) is needed. That can be an impulse, a set of impulses or a continuous energy stream, for example a finger, bow, stick or air stream. The power of the input energy determines the amplitude of the vibrations and thus the loudness of the note. Examples of vibrators and exciters are shown in the table (below).

Tone production in various instruments

The vibrator of string instruments can be considered almost one-dimensional (line) and the membrane of a timpani two-dimensional (plane), whereas brass players´ lips are clearly a three-dimensional, very complicated vibrating mass. The fundamental principle, however, remains similar in every case. The properties of a vibrating system determine its characteristic frequencies and the input energy gives the kinetic energy needed for vibrations. In many instruments it is possible to adjust both the characteristic frequencies and the amount of excitation during the tone production process, and thus generate different pitches and volumes of notes. A string player, for example, can adjust the pitch by the length or tension of a string and the input energy with the bow or finger (pizzicato). A timpani player adjusts the pitch by changing the membrane tension, and the input energy with the sticks. A brass player has to adjust his or her lips to produce a certain characteristic frequency, and this must be in balance (co-operation) with the air column’s characteristic frequency inside the instrument. Using the air stream, a brass player can adjust the amount of excitation energy, but not the pitch of the note. Very good efficiency is necessary to produce a soft tone. If there is a lot of wasted air streaming through the lip aperture, there will also be a lot of extra noise, and pianissimo playing will be impossible. The reason for this could be a lip aperture that is too big or something else that prevents free lip vibrations. “More air” doesn’t solve this problem, but only makes the note louder or wastes more air. The air stream blown through the lip aperture of a brass player gives vibration energy to the lips thus making the note louder or softer (amplitude), not higher or lower (frequency).

A string player cannot adjust the pitch with the bow or a timpani player with the stick – the vibrator and the exciter simply have different roles, and it is not possible to switch them from one to the other. The situation is the same in brass instruments.  The vibration frequency of the lips depends on the properties of the lips themselves, and they must be adjusted during playing to produce the desired pitch. A steady (stable) note is produced by keeping all of the variables as constant as possible.

In reality, a brass player’s lip movement is a complicated combination of various movements in many directions. In a slow motion film it looks like a liquid surface in wave motion (the lip tissue is mostly water). These movements are very individual, but follow the same laws of nature for every player.

Sounds of different instruments

Printable version