Timbral effects of col legno tratto techniques on bowed cello sounds

There are several playing techniques for bowed-string instruments that make use of the wooden stick of the bow. The stick is quite often used to strike the strings gently (col legno battuto) and less commonly to bow on them (col legno tratto). Col legno has existed since the 17th century, and it is often used in modern compositions. When the stick is drawn across the string (tratto), the contact between the scrubbing stick and the string introduces noise. The player may choose to combine both hair and stick, depending on the desired sound. To evaluate the timbral effects of col legno tratto on the cello sound, the current study compares three variations across ordinary and contemporary bowing techniques: using only the hair, using both hair and stick, and using only the stick. Motion capture and audio-video recordings with expert cello players show how the bow tilt varies greatly between the three cases. Suitable audio descriptors of timbre are evaluated, which may help to correlate the observed playing parameters and sound properties with the semantic attributes used by experts to describe the timbre of these techniques.