Vibrato and String Tone
On top of this, stringed instruments are normally played with vibrato. Think of listening to a string quartet at a concert at a wedding, and watching the musicians left hand, the fingering hand. You will see that they are wobbling their hand about, backwards and forwards in a fast rhythmic motion. This results in the note wobbling up and down slightly. They do this to create a warmer sound (to some reason our brains and ears interpret this variation in pitch as warmth and depth of note, that I'm not quite sure of the physics lies behind that of the perceptual neurology of it). This has the effect of covering up the changes of pitch that happened due to low pressure and the vibration of the string and variation of its tension in friction/stiction scenario.
As I said, if you watch a string quartet playing their instruments, you will see the left hand doing this vibrato, but in barn dance band or ceilidh band you may not see this being done. There are 2 reasons, firstly a lot of barn dance music is very fast, and if you thrashing through the notes at a rate of knots, there is no time or necessity for vibrato. On longer notes, there is a need for vibrato if the note is going to sound nice, but not all folk fiddler's are skilled enough to do vibrato (is very difficult and quite painful to learn. Once you can do it, you can keep doing it all day, but until your muscles have been trained for this – I suppose it's muscles and brain combined that cause this to happen – but until the train is complete it's very painful on the muscles, and young pupils regularly complain "my hand hurts Sir, can I have a rest now?" The answer from a cruel teacher like me is "NO! Learning to play a violin is about learning to conquer pain!)"
Has now compare the notes and the instrument plays with those of the brass and woodwind instruments we've viewed earlier. There are 2 kinds of note, open and stopped. The open notes of those which are produced by the natural tunings of the strings, which are G, D, A, E. The open strings have quite a different quality of sound to the stop strings (stopped being a note produced by pressing a finger against the string to clamp it to the fingerboard). This is important, in that any of these notes, except the open G can be played either as an open string (i.e. not stopped note) or as a stop note on the string below it.
This difference in sound quality is used extensively when playing string quartets. The stopped note is more mellow and can have vibrato applied to it (the open string, obviously can't have vibrato applied to it as the left hand isn't touching the string and it is the left hand that produces the vibrato). This contrast in tonality means that if the note wants to be warm sounding, use the stopped note, and if you want the note stand out as harsh and unwavering note, you can use the open string. Open notes can be extremely effective when playing string quartet arrangements Piazzolla tangos, which are about charming subjects like death and murder and muggings in the streets of Rio de Janeiro.
Sometimes, a series of notes played on the same D, A or E will have some of the notes played as stop notes and other ones as an open string, to give contrast and interest to the line. The open strings can also be used to produce a sort of trumpeting sound, which can be relevant to playing string quartet music for weddings, for example when announcing the entrance the bride or during the recessional. In a symphony orchestra, the open string is almost always avoided, because it's harshness and brilliance stands out like a sore thumb from the rest of the violins, and the object is for all violins to blend in to one sound. Occasionally the whole string section will use open strings, but only if specifically directed to do so by the composer.
Open strings are used extensively in ceilidh band and barn dance band music, especially when playing American barn dance music which relies on an open string being played together with the stop string to achieve its characteristic ye ha sound. Other times, open strings are just lightly touched on from time to time to give emphasis and the folky feel. Jazz violin playing is much more like classical solo playing, where most the time playing an open string is avoided.
In addition there are notes known as harmonics. There are 2 kinds of these, natural and artificial. A natural harmonic is achieved by placing a finger extremely lightly on a "node" which breaks the subsidiary vibrations of the string and produces an attenuated sound one octave above the written note. With an artificial harmonic, the string is stopped with a finger in the normal way, which effectively shortens the length of the string that can vibrate. Another finger is placed lightly on the node of that shorten string to achieve the same effect. Bartok uses this technique extensively in his violin sonatas.
Another way of affecting the quality of the sound is to vary the position of the bow contact on the string, and by position I mean how close it is to the bridge or how close it is to the fingerboard (this is a small variation in distance of about 3 cm that has to be held accurately as the violinist pumps the bow up and down at great speed, but it is critical to the nearest millimetre or 2, especially when playing near the bridge.
A lot of the time during playing the bow lies midway between the bridge and the end of the fingerboard. When playing quietly, the bow is usually shifted towards the fingerboard (though not always, it can remain near the bridge if a penetrating but quiet sound – if that makes sense to you, but it certainly is possible and real – is required). If you want a loud and penetrating sound you move very close to the bridge. This is a dangerous place to play in, because a millimetre too close to the bridge and the violin can make horrible squeaks. The first violinist of the string quartet, and soloists who play violin concertos, get very good at playing near the bridge is this the way to get the sound to carry to the back of a concert hall, and the tune of the string quartet generally has to carry well.
There are also certain orchestral effects which are achieved by playing with the hairs the bow on the bridge itself. Of course any hairs that are actually on the bridge are going to have negligible effect, but some of the hairs do touch the string on the fingering side and cause a small amount of vibration, and other hairs touch the string on the nonplaying side which creates a sort of squeaking hiss. If you get one violin doing this it sounds horrendous, but if you get a large group of violins, say a dozen first violins, doing this, the overall effect can be extremely atmospheric. This technique that is quite often used in the suspense parts of film music.
There are still more ways of making a noise on the violin. Sometimes a piece of music will have written against the notes the direction "col legno", meaning with the wood, and here we mean the wood of the bow stick. The bow has to be turned upside down to do this, and one taps the string, or sometimes bashes it quite violently, with the wood of the bow. Because the elasticity of the string, the bow bounce is right off it, giving a sort of clicking percussive sound that has a bit of note pitch attached to it. Some pieces of quartet music ask for this, but it's a technique that is more often found in orchestral writing.
There are all sorts of bowing techniques like detache, stacato, spicato, legato et cetera which are all to do with how long the bow stays on the string, and how much you can hear the change in direction of the bow. The bow isn't a continuous band (although I continuous bow is effectively used in the old-fashioned hurdy-gurdy, where a friction wheel is rotated against the string, the wheel going round continuously so effectively being like a violin bow of infinite length.) Because the bow is not continuous it has to go up and down like a piston. When it changes direction, the string stops vibrating from moment, and then begins again as the book celebrates the opposite direction. Sometimes you want to hear this stuffing of the sound, sometimes you want to avoid hearing it, and there are all sorts of bowing techniques that accentuate one feature another. If the piece of music is to be played legato, then you don't want to hear the sound of the boat changing direction.