Acceptance limits for the duration of pre-Helmholtz transients in bowed string attacks

Abstract

The attack of most bowed notes shows an initial part before Helmholtz triggering occurs (the pre-Helmholtz transient), during which the stick-slip interaction promotes frequencies other than that of the string’s fundamental. Depending on the particular combination of bowing parameters, this state is characterized either by periods that are prolonged, or by a division of the period into two or more parts, multiple flyback. An onset with perfectly periodic motion (Helmholtz triggering) directly from the very start is also possible. A sample of violin tones representing these three classes of attacks, and with different duration of the pre-Helmholtz transient, has been collected by the use of a computer-controlled bowing machine. The tones were evaluated by 20 advanced string students and professionals in a listening test, judging the acceptance and quality of the attacks. The maximum acceptable duration of the pre-Helmholtz transient was estimated to 50 ms (⩽10 nominal periods, open G string, violin) for attacks with prolonged periods, and 90 ms (⩽18 periods) for multiple-flyback attacks. These values refer to a neutral start in a neutral context, such as when practicing a scale. A playing test, in which the performances of two professional violinists were analyzed, confirmed these results, and showed that the same limits apply to a larger group of bowing styles as well.