Dept. of Computer Science, University of Copenhagen Universitetsparken 1, Dk-2100 Copenhagen Ø, Denmark

Transcription

1 NORDIC ACOUSTICAL MEETING JUNE 1996 HELSINKI THE CONTROL MECHANISM OF THE VIOLIN. Dept. of Computer Science, University of Copenhagen Universitetsparken 1, Dk-2100 Copenhagen Ø, Denmark 1 INTRODUCTION Historically, the control of a musical instrument has always contained different grades of closeness. For instance, when playing a bell, you just strike it with the hammer, whereas in the human voice, you have continuous control of many dimensions of the sound. In this paper, the controls of the violin are investigated, and a set of continuous control parameters necessary to fully exploit this instrument are proposed. The intent is to estimate the number of parameters necessary to control a good instrument, rather than create a protocol for controlling a synthetic musical instrument. The violin is a bowed, or a plucked instrument. In the first case, the amplitude is continually controlled by the bow, whereas in the latter case the amplitude follows a predefined envelope. Likewise, the pitch and different timbre dimensions can be analysed as being a function of the movement of the bow, and the fingers of the left hand. The result is a list of parameters and their possible values, which will be depicted with their perceptual influence on the sound. 2 THE VIOLIN The violin [1],[2] is a bowed string instrument, which share the control characteristics with most of the other instruments in this family. The bowed instruments include the violin, the viola, the cello, and the contrabass. The violin is tuned G3, D4, A4 and E5. The range of each string is about 2 octaves. The violin has the following parts, which are of interest to us: strings, fingerboard and bridge. The bow is constituted of bow hair, and the hair length is about 65 cm. The sound is produced when the bow is touching the string. The string often continues to vibrate after the bow no longer touches it, thus producing an envelope-based sound.

2 THE CONTROL MECHANISM OF THE VIOLIN The amplitude of the sound is dependent on the speed of the bow, the force (pressure) of the bow, and the position of the bow on the string. The faster the bow, the louder the sound, and the closer to the bridge of the string the louder the sound. The amplitude of the violin is roughly proportional to the force of the bow. This force has a maximum and minimum value, which are a function of the position of the bow. The onset of the sound also changes with the force of the bow. With less force, the higher harmonics develop faster than the fundamental, whereas when the force increases, the fundamental develops as fast as the harmonics. 2.1 The static modifications The following are a list of modifications to the violin and to the bow, which can change the characteristics of the instrument, but which cannot be done while playing a note. The bow hairs can be rubbed with rosin and the hairs can be stretched, or released. The material, quality and tension of the strings of the violin can also be changed. Of course, the acoustics of the room the violin is played in is also very important for the sound. 3 THE BOW TECHNIQUES The position of the bow may change the timbre significantly. When the string is played on the fingerboard, the sound is more mellow, but it becomes hard, metallic, when the bow is close to the bridge. The angle of the flat of the bow to the string also change the amplitude. The bow consists of many hairs, more of which touches the string when the bow lays down on it, making the sound louder, more forceful, than when the bow tilts. The sound also gets brighter when the bow tilts, Figure A. The Violin. From [1] than when it touches the string completely. This effect also occurs when the force of the bow is diminished. The angle of the long of the bow to the string can also be changed, although this is not common in violin music. When this angle is not 90 degrees, the sound becomes harsh, inharmonic. This is due to longitudinal vibrations of the string. Most often, it is impossible to create a normal tone at the same time as a longitudinal vibration. It is important to notice that the bright flutelike sound emanating when pressing the bow lightly against the string, is not the same as the harsher sound when stroking the bow close to the bridge, which is also not the same as when playing the long of the bow at an

3 THE CONTROL MECHANISM OF THE VIOLIN angle to the string. These timbre changes do not easily permit to modify the sound so that it is not recognised as a violin. This is of course one of the virtues of this instrument, it has an easy and subtle control over many parameters of the sound without trespassing the identity of the instrument. 4 THE LEFT HAND The left hand is controlling the pitch of the note. This is done by moving a finger up and down the neck, or by changing the finger, thereby changing the length of the vibrating part of the string. The position of the finger and the string played on both changes the timbre as well as the pitch. The pressure of the finger against the string can also change the timbre slightly; when releasing the pressure, the sound dies, or muffles. Another way to silence the sound with the left hand, is by putting a finger on the vibrating string. This technique can also be used to create flageolets. The instrument produces harmonics when placing the fingers lightly at certain points, more exactly the nodes of the octave, the fifth above the octave, or the second octave. So called false flageolets occurs when a note is held with the first finger, and the harmonic, most often the second octave, is produced with the fourth finger. The sound is dying away faster, when moving the finger up the fingerboard, than when moving it down. Other parameters of the sound includes the position and the direction of the violin. 5 PERFORMING TECHNIQUES The violin is played by stroking the bow over one or more of the strings [2], [3], [4]. The right hand is holding and moving the bow, and the left hand is pressing the strings down on the neck. Generally, the violin is held in place by the jaw, which is pressing the body of the violin down on the shoulder of the player. A good player can keep an perfectly constant tone on changing the direction of the bow. 5.1 The bow The different playing techniques are: detaché (change the bow direction, or releasing the bow, for each note, thereby detaching them), legato (the notes are not separated), martelé (the bow is first pushed on the string, then released and advanced, then stopped), staccato (series of hammered), spiccato (the bow is jumping on the string), flying staccato (release the bow on the string, thus letting it jump), and tremolo (a rapid movement of the wrist, thus causing a trembling tone). Several other techniques exists, the majority being intermediate between the above techniques. These techniques are essentially a function of the elasticity of the bow, the hand, the arm, and the string, combined with the force of the bow against the string.

4 THE CONTROL MECHANISM OF THE VIOLIN In the contemporary music the playing techniques are, col legno (using the tree of the bow), col legno battuto (hitting with the wood), sul ponticello (on the bridge) and sul tasto (on the fingerboard). 5.2 Pizzicati When the string is fingered it is called pizzicati. The timbre and the amplitude can be varied by changing the angle of the finger, the position plucked on the string, and the force of the pluck. The plucking can also be performed with the left hand fingers. 5.3 The left hand The left hand are performing vibrato, flageolet (making the string vibrate at a harmonic frequency), demanché, and glissando. The timing of the left hand finger position change versus the bow direction change is very important. If the bow direction change before the finger position, then the legato effect is completely lost. The finger must change position before the bow direction changes if the legato effect is desired. 6 SUMMARY These are the parameters which have a perceptual influence on the sound of the violin. The parameters are stated with their maximum and minimum values or the extremes. 6.1 The bow The speed of the bow. Fast. Slow. The direction of the bow. Up. Down. The position of the bow. Close to the bridge. Close to the fingerboard. The force of the bow. Light. Hard. The angle of the flat of the bow to the string. Straight. 90. The angle of the long of the bow to the string. Straight. 90. The 'elasticity' of the bow. Firm. Loose. 6.2 The left hand String chosen. Left hand finger position.

5 THE CONTROL MECHANISM OF THE VIOLIN Left hand vibrato speed. Slow. Fast. Left hand vibrato extend. Small. Large. Left hand glissando. Up. Down. Left hand light touch position. At harmonic point. At silence point. 6.3 Silencing Stopping the bow while pushing the string. Releasing the bow. Releasing left hand finger. Pushing left hand finger gently on the string. 6.4 Other Violin Angle Violin Slope Violin Direction Violin Position. x,y,z. Left finger change timing. Before the bow change. After the bow change. All of the above movements are independent, that is, it is possible to perform by changing any one, or all of the above parameters continually. It is this large control of the many and well defined timbre dimensions that makes the violin such a popular and loved instrument. These controls, which have evolved through the centuries into this state of perfection, are probably what is needed in a performance electronic instrument. 7 REFERENCES 1. Neville, H.F. & Rossing T.D. The Physics of Musical Instruments. Springer- Verlag, Bachmann, A. An Encyclopaedia of the Violin. DaCapo Press, New York, Martins da Fonseca, A. Private Conversation Hansen, K. Private conversation