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Musical instruments are divided into groups by the way in which they make the sound. Wind instruments use air blowing through the instrument. They are divided into three subgroups:
Brass instruments use vibrating air inside the instrument and start the sound using the vibration of the player's lips.
Woodwinds use vibrating air inside and start the sound by some means other than vibrating lips, such as a hard edge or a vibrating reed.
Free reeds use a vibrating reed but no vibrating air chamber.
What is a Woodwind?
The woodwind section in an orchestra consists of flute, clarinet, oboe and bassoon. All these were originally made of wood, which gave the section its name. Nowadays, flutes are usually made of metal while clarinets and oboes may be made of plastic. Many other instruments besides these four are also considered to be woodwinds, including recorders, saxophones and even bagpipes.
On the other hand, the didjeridoo and the alpenhorn are both wooden instruments that you blow into, but they are not woodwinds. They are considered to be 'brass' instruments, because they work on the same principles as other brass instruments.
The harmonica or mouth organ is a reed instrument you blow into, but there is no chamber of vibrating air. The pitch is entirely determined by the shape and hardness of the reeds. This is a free reed instrument.
The pipe organ (church organ) is technically a woodwind instrument by the definition given above, but it differs in so many ways from all other woodwinds that it should really be considered in a category of its own and will not be discussed here.
Pitch on a Woodwind
Most woodwinds consist of a tube of air with a source of sound at one end. The source may be a hard edge against which air is blown or a flat piece of wood called a reed over which air is blown. In either case, a sound wave travels down the instrument. Some part of this is reflected as it meets the open air at the other end of the instrument. If the wavelength is such that the wave going down the tube is reinforced by the reflection coming up the tube, then a 'standing wave' is set up. This happens when the wavelength is twice the length of the tube. A tube of 66cm will support a musical note of wavelength 132cm, which corresponds to a frequency of 262Hz or 'middle C'.
So the fundamental sound produced by a tube is determined by the length of the tube. The longer the tube, the lower the pitch; the shorter the tube, the higher the pitch. For example, a sopranino recorder is about 24cm long and produces a basic note of F5 (2 Fs above middle C). The Great Bass recorder is about 120cm long and has a basic note of C3, the C below middle C.
The clarinet is an exception to this general rule. Due to a pecularity of construction, it produces a much deeper note than other instruments. It is discussed in a separate section.
There are three ways of changing the pitch of the note produced. These are discussed in the next three sections.
The effective length of the tube can be changed by opening holes on the side of the tube. Since most of the air will go out through the hole, it is as if the tube has been shortened, so the pitch rises. Almost all woodwind instruments use these 'tone holes'. In some, they are covered by the finger tips. In others, a system of pads, levers and keys is used to cover the holes, and these are controlled by the fingers. Woodwind instruments place a much greater reliance on fingers than brass instrumnets. A typical brass instrument has only three or four keys. A clarinet has seven holes and 17 keys to be operated using nine of the player's ten fingers. The bassoon has so many keys that the left thumb alone has to manage ten separate keys.
The second way of changing the pitch is to change the way the vibrating wave fits in the tube: if two waves can fit in the tube instead of one, the pitch will rise by an octave. This is normally done by a combination of blowing harder (overblowing) and opening strategically placed small holes along the tube. All the notes will go up by an octave together. These new notes are called 'harmonics'. A set of notes all using the same harmonic is called a 'register'. The lowest register is based on the fundamental notes; the next register is normally an octave higher, and consists of notes at the first harmonic. In some instruments, there are higher registers using second or third harmonics.
Again, the clarinet is an exception to this.
Embouchure means the way you hold your mouth. In a flute, the lips are pursed to direct a stream of air against a hard edge. In an oboe or clarinet, the reed is pressed against the player's lips. In all these instruments, changes in the shape of the mouth and increases in pressure can make a slight change to the pitch. It is possible for a good player to drop the pitch slightly if playing in a group where the other instruments are lower than standard pitch.
Instruments such as the recorder offer almost no possibility of changing the pitch in this way, because the breath of air is directed by the instrument itself against the edge. In the same way, the reed in bagpipes is not placed in the mouth, so can not be affected by the embouchure.
The Acoustic Peculiarities of the Clarinet
The clarinet has a cylindrical bore and a single reed at one end. The combination of these two features give it an unusual acoustic property. It produces a note an octave lower than other instruments of the same size. The note produced lacks many of the harmonics that would normally be present in a musical tone: harmonics with a frequency which is an even multiple of the fundamental frequency are very quiet, while the odd multiples are loud. This gives the clarinet a very distinctive sound.
Because the even multiples are quiet or not present, it is not possible to 'go up an octave' by overblowing. Instead, the first register above the fundamental is at a frequency three times the fundamental frequency, so it is an octave and a fifth higher, or 19 semitones. The basic scale of the clarinet is an F major scale: F G A Bb C D E F. When this is shifted to the next register up, it becomes a C major scale: C D E F G A B C. This seems very peculiar to players of other instruments such as saxophone, flute and oboe!
The Main Types of Woodwind
These have a reed consisting of two flattish pieces of wood bound together back-to-back so that there is a narrow gap between them. In most double reed instruments, the reed is placed between the player's lips, giving the player great control over the sound. Instruments of this type include the oboe, cor anglais and bassoon, the Middle Eastern shawm and the Breton bombard.
The double reed makes a very buzzy sound which can be described as nasal in its higher reaches and gruff in the lower reaches, such as in the bassoon. This distinctive sound carries well above other instruments, so it is very suited to playing solo lines with an instrumental backing. The oboe is a very respected solo instrument.
The double reed may also be 'capped', which means that it is contained in a chamber within the instrument so that nothing touches the vibrating tip of the reed. This is the case with bagpipes. Because there is much less control of the reed, it is rare in such instruments to be able to reach any of the higher registers. The range of the instrument is usually very limited. The Scottish bagpipes, for example, have a range of only nine notes. Another capped double reed is the 'snake charmer' played by Indian fakir musicians. This has a double reed inside a gourd with a pipe coming out of one end.
This family includes clarinets and saxophones. There is a single flat reed which is strapped so that it covers a slot in the side of the mouthpiece. The single reed gives a much smoother sound than a double reed. As discussed earlier, the clarinet also has an acoustical peculiarity (reed + cylindrical bore) which makes it play an octave lower than other instruments, giving it a wonderful dark tone.
Other single reeds are the chalumeau which is an early proto-clarinet which is still seen occasionally for playing early music, and the taragato, a Hungarian instrument like a straight saxophone made of wood.
'True flute' players must use their lips to direct a jet of air against a hard edge to produce the sound. In transverse flutes, the player blows across a hole in the side of the flute. The whole flute is held sideways, across the body. In pan pipes and shakuhachis, the player blows into the end of the pipe, the hard edge being the side of the pipe. This gives a very breathy sound. True flutes have a very pure tone. In the concert flute, this tone is enhanced by subtle shaping of the bore and the end plug to make a tone lacking the breathiness of other flutes.
A duct flute player blows into a tube called a 'windway', and the other end of the tube directs the airflow against the edge. Among the duct flutes are recorders, tin whistles, flageolets and ocarinas. Duct flutes are easier for beginners to play because the player does not need an advanced embouchure. They are generally more limited in the range of different volumes that can be produced. Since there is no variation in the air striking the edge, all the music comes out at the same volume. Blowing harder will produce a louder note, but will usually sound sharp. A true flute player can adjust the embouchure to allow for this.
Ocarinas are a type of duct flute, but they are different enough from the others to merit a special section of their own. An ocarina is a ball-shaped instrument normally made of baked clay or plastic. It has a windway and sound-producing edge, and the air in the chamber inside the instrument resonates to make the note.
The ocarina is the only wind instrument that doesn't rely on a long thin (cylindrical or conical) column of air resonating to produce the sound. The ball-shaped chamber resonates in a different way to an air column. Technically it is a 'Helmholtz resonator'.
There are finger holes on the ocarina, but the exact position is not as important as the number of them that are open at any time.
Ocarinas were independently invented in at least two places: in South America, since ancient times, they have been made in a circular shape with four to eight fingerholes, and occasionally in the shape of an animal. In Italy, the ocarina was invented in the 18th Century in a teardrop shape with eight to ten fingerholes and a sideways-pointing windway. It is held like a transverse flute.