Pressure Types

The typical bowing position.
At very low pressures, the timbre has a particular thin quality: flautando or flautato. This ‘thin-sounding’ spectrum is caused by the strength of the mid-range partials in relation to the weakness of the fundamental and upper partials.
Extreme increases in bowing pressure can be controlled in order to produce various sounds. The controlling factor of these sounds is the relationship between high bow pressure and bow speed, which creates distorted noise.
Air noise is very similar to flautando bowing but with very little pressure, producing white noise with almost no perceptible pitch. The left hand is used to mute the strings and the pitch quality will vary according to the string on which it is played: if a higher string is used then the air noise will be higher and thinner in tone than if a lower string is used.
Scratch noise is very similar to​ crushed bowing but with the addition of the left hand being used to mute the strings so that no identifiable pitch is produced. The resultant white noise corresponds to the pitch of each string: if a higher string is used, the air noise will be higher than for a lower string.

Bow Placements

Bowling near or over the fingerboard. This is employed in order to produce a much softer, ‘woodier’ and less defined sound than one would produce in the normal bowing position. The pitch has much more fundamental pitch and less of the overtone series.
Bowing nearer to the bridge creates a harsher sound filled with overtones and less of the fundamental pitch, increasing as the bow position moves closer to the bridge.

Bow Air Sounds

Circular bowing, in addition to the standard frog-to-tip bow direction, requires the performer to make a circle with their right arm during the bow stroke. This creates pitch as well as bow hair noise during each rotation. The rhythm, speed and circumference of the circle can be free or specified.
If the hair of the bow is placed on the string, pressed into it then pulled upwards with no horizontal movement, a dry creak is produced. The intensity of the sound increases and with increased pressure and with the speed of the articulation.
With this technique it is possible to play simple legato phrases in a very high register.
The best results can be obtained by bowing behind the left hand very close to the nut.
The bow hair is placed on the string, and excess downward pressure exerted whilst moving the bow in an up and down motion.
The hair can be used for a batutto type articulation and is most effective when used toward the tip where the hair is most taut. If the middle of the bow is used, high dynamic levels will also include a percussive articulation from the bow wood. The clarity of articulation diminishes closer towards the frog.
This is a similar technique to batutto with hair. The area of bow hair used is very near the tip. In addition to the strike, the bow hair moves very slightly in the normal bowing direction, creating friction against the string, producing a pizzicato-like sound.
Helicopter bowing is a combination technique involving arco diagonale, bow vibrato and a gentle side-to-side bow motion. As the bow is drawn, the bow should produce a vibrato at the same time as moving in a slightly upwards or downwards motion. This can be executed at a variety of speeds.
It is possible to simultaneously activate parts of the harmonic spectrum in conjunction with the open string sound and vary the degree to which the overtone is audible in relation to the open string sound. As an open string sound is made up of the fundamental plus its overtone series, it is possible to isolate a harmonic frequency within that spectrum and amplify it, in this case with the bow, which acts as a finger on the node point of the vibrating string to allow the overtone to become clearly audible.
Standard string technique includes the use of a left hand vibrato. It is possible to vary the degree of vibrato from senza to molto.

Sounds Produced with Bow Wood

The strings are struck with the wood of the bow. In addition to the intended pitch, col legno also produces a subsidiary pitch which varies according to the placement of the bow. As the bow strikes the string closer to the bridge the pitch ascends and vice versa.
The bow wood is drawn across the string as one would with the hair. The dynamic range is limited to the quieter end of the spectrum but produces a definite pitch in combination with the noise.
As with typical batutto performance, the bow wood strikes the string and is allowed to ricochet giving several reiterations of pitch.
After pizzicato and with the natural vibration of the strings, playing minutely with the frog tip near the bridge, the sound produced is really fascinating.