Who would believe that by making a Bronx cheer into a metal tube one could make beautiful music? But, this is the world of brass instruments!

The intention of this article will be to identify how this hollow tube performs that miracle of sound, and along the way perhaps discover why tuning problems still plague even our most competent players.

Creating sound...

Music results when vibrations create sound waves. The speed or frequency at which these vibrations occur determines the pitch perceived by the ear:  The faster the vibration, the higher the pitch.

Just as the string is the source of vibration for the violin, so the lips are for brass instruments. By blowing air through a tube, sound waves are set up inside the tube which acts as a resonator and amplifier according to the frequency of vibration of the lips.

On a violin string only one pitch can be produced, that is, until the vibrating length is altered through pressing the string against the fingerboard. But because of the flexibility and large mass of the human lip, a whole series of notes can be produced on a fixed length of tubing. This phenomenon is known as the ‘harmonic series.’

The character of music in our western culture (as opposed to Chinese, say) depends on a system of twelve equal semitones to every octave; equal temperament. Because the basic tube produces an overtone series that conforms to the natural laws of physics and not to this man made system, it must be adapted to make it usable. The addition of a mouthpiece and a bell help to bring the overtone series into something close to our equal temperament.

So far the hypothetical instrument we have considered is something like a bugle, in that it would play only the notes of the harmonic series. You will notice that higher up in the harmonic series the notes become closer together. In the Baroque period when trumpet playing flourished, the length of the trumpet was roughly twice what it is today so that it could be played in the upper register where more notes were available. But, this instrument would only be playable in one key, so additional pieces of tubing (crooks) were designed to make ti possible to play in different keys.

Why we need valves...

To fill in the gaps between the notes of the harmonic series, i.e. to make possible all the notes of the chromatic scale, the length of tubing would need to be variable while playing the instrument.

The trombone uses the simplest method of varying the length by use of an adjustable slide. Other instruments bring extra lengths of tubing into use by valves or pistons which redirect the air flow. The second valve lowers the pitch by one semitone; the first valve by two semitones, the third valve by three semitones.

What about intonation?

To lower the sound one semitone requires a six percent reduction in the frequency of vibration, hence a six percent increase in tube length. The amount of additional tubing needed to lower the pitch for each subsequent semitone would be greater, and this is precisely where built-in tuning problems occur. We can’t expect the same piece of additional tubing to alter all notes by exactly half a step; six percent of a 50 inch tube is not the same as six percent of a 60 inch tube.

To accomplish this in a valve instrument we need a compromise. As can be seen in the diagram, valves one and two are made slightly too long so that when they are used in combination, the resulting note will only be slightly sharp.

The third valve is longer to give slightly more than three semitones, so that the combination with other valves will not be too far off.

Obviously, the most out of tune combinations will be those using the most valves: 1/3 for low D, and 1/2/3 for low C sharp.



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The intent then with compromise tuning is to make some notes a little flat so that others will not be too sharp. Notes using valves will not be perfectly in tune; neither will they be too far off.

When the compromise tuning built into the modern instruments fails to overcome problems in the physical properties of the instrument, it is left to the performer to blow it in tune, using the lips to affect the pitch slightly. This can only be done to a small degree before the tone begins to suffer.

Modern manufacturers, however, have come up with several devices to improve intonation on valve instruments. High quality cornets, for instance, will feature first and third valve slides that are finger adjustable so that notes using valves one and three can be individually tuned.

Compensating Systems...

For larger instruments, finger adjustable valve slides are generally impractical because of the size of tubing. Most large instruments now have a compensating system which brings into use extra crooks only when certain valve combinations are used (see diagram below). This compensates for the progressive nature of the physical problems involved in low end valve combinations.



(Click here for larger picture)

Some euphoniums and tubas have a fourth valve which lowers the pitch by a fourth, making it possible to play low D and C sharp in tune. The fourth valve also makes it possible to play a fourth lower in combination with other valves. The progressive problem of intonation will still effect these combinations.

Get to know your instrument...

Problems of intonation are different from instrument to instrument, and even from model to model. The secret, then, is to get to know your instrument. Find out which notes tend to be out of tune and decide what to do about it. Experiment with the moveable slides and alternate fingerings. You will be able to improve certain notes immediately. To help you further unlock the secrets of your particular instrument you might use an electric tuner.

Temperature also can affect intonation. Anyone who has done outdoor serenading at Christmas time will realize that the cold air does funny things to their tuning. Since sound waves travel more slowly through colder, denser air, we actually hear a lower pitch. A change in air column temperature from 2.7º C to 32.2º C will cause a difference in pitch of a full semitone.

A discussion of intonation must include a word on centered sound. To truly get the best from the instrument a player must find the center of each note and in so doing the whole instrument will resonate in a characteristic manner. This ‘sweet-spot’ effect is the player’s first clue that he is on his way to playing tunefully. No, the instrument can’t do it all alone.

Musicians will never be totally free from problems of intonation. However, understanding the instrument and the basic reasons for these problems is the best step to eliminating them. In the final analysis the ear is the most important tool we have. When we can understand, listen and apply what we know, we are well on the way to making tuneful music.