In classical and modern symphonic orchestras, there are usually four different brass instruments which can be paralleled to the four human voices of the choir: the Trumpet (soprano), the Horn (alto), the Trombone (tenor), and the Tuba (bass).
The most important basic features which characterize Brass instruments are:
1. a relatively long tube that is coiled in a variety of shapes, which makes it possible for a player to handle the instrument;
2. a special mouthpiece in the shape of a cup or small bowl, which is inserted into the the thin end of the tube;
3. a flared bell at the other end of the tube; and
4. valves, pistons, and crooks in three of the brass instruments and a mobile slide in the Trombone.
Players produce sounds with the brass instruments by blowing air through their lips, which are tightly held against the cup-shaped mouthpiece. The air sets the player's lips in vibrations, which in turn vibrates the column of air in the tube. By changing the tension of his lips, the player can obtain different tones. Relatively loose lips are used for low tone, while tight lips are better for high tones.
The shape of the mouthpiece, as well as its size, greatly influence the characteristic quality of the tones produced. The Horn, for instance, has a cone-shaped opening in its mouthpiece. This shape helps to produce a relatively soft and mellow sound. When the cup is shallow, as in the Trumpet, a brilliant sound is produced.
There are many types of mouthpieces, and each player may select the one he believes is best. Some of the various mouthpiece forms can be seen in the picture.
The length of the tube determines the Fundamental note of the instrument, which is also its lowest tone.
When the player blows air through the mouthpiece of any brass instrument, he can produce only a limited number of different notes (called "harmonics"). By changing the tension of the lips, the player can produce any harmonic he chooses.
When the length of the tube is changed, another fundamental note can be produced as well as a series of harmonics, based on the same Intervals as the harmonics based on C. The player must be able to pick out the desired note by using the appropriate lip tension.
If the player wants to change the pitch of the fundamental note, he has to shorten or lengthen the tube. This can be done by fitting longer or shorter pieces of tube called "crooks". Today, modern brass instruments have valves which, with the aid of pistons, can alter the length of the tube by adding an extra loop of tubing.
The Trombone is the only instrument in the brass family which does not have valves; this problem is solved by the use of its mobile telescoping slide. The valves were invented in the beginning of the 19th century, but it took some time before they were adopted for these instruments. The valves are illustrated here.
The sound of the brass instrument can be softened and subdued by inserting a mute into the bell. There are many kinds of mutes. You can see some of them in the illustration.
Since players of brass instruments have to blow much more air than woodwind players, the composer must take this into account by inserting rests in appropriate places in the score. There is an additional problem: since a great amount of air is blown, some of it condenses, forcing the player to get rid of the water. The player gets rid of the water by using a "water key", or by pulling out the valve slides.
The brass family is relatively loud and can easily drown out all the other orchestra instruments.
