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The attack of most bowed notes shows an initial part before Helmholtz triggering occurs ͑the pre-Helmholtz transient͒, 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 triggering͒ 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 ͑р10 nominal periods, open G string, violin͒ for attacks with prolonged periods, and 90 ms ͑р18 periods͒ 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.

The attacks of most bowed notes on a violin show a nonperiodic initial part before Helmholtz triggering occurs. Depending on the particular combination of bowing parameters, this state is characterized either by periods which are prolonged, or by a division of the nominal period into two or several parts, multiple flyback. A ‘‘perfect’’ onset with only one slip per period from the very start is also possible. The present study includes: (a) computer simulations of a violin G-string and characterization of the attack quality as function of bowing parameters; (b) evaluation of acceptability of a series of (machine-bowed) violin attacks with respect to duration of the pre-Helmholtz triggering; the evaluation took place in a listening test that involved music students and professionals; (c) analyses of 1694 attacks in different musical contexts as performed by two professional violinists. The limits for acceptability established by the listening test were about 50 and 90 ms of prolonged and multiple-slip periods, respectively, for an open G-string (196 Hz). These demands were confirmed by the playing test, even for other strings and a larger group of bowing styles. [Work supported by The Nordic Research Council.]

By carefully positioning the bow and a lightly touching finger on the string, the string spectrum can be conditioned to provide narrow bands of pronounced energy. This leaves the impression of multiple complex tones with the normal (Helmholtz) fundamental as the lowest pitch. The phenomenon is seen to be caused by two additional signal loops, one on each side of the finger, which through the repeating slip pattern get phase locked to the full loop of the fundamental. Within the nominal period, however, the slip pulses will not be uniform like they are during the production of a normal "harmonic" or "flageolet" but may vary considerably in shape, size, and timing. For each string, there is a large number of bow/finger combinations that bear the potential of producing such tones. There are also two classes, depending on whether the bow or the finger is situated closest to the bridge. Touching the string with the finger closest to the bridge will somewhat emphasize the (Helmholtz) fundamental. The technique is applicable to double bass and cello, while less practical on shorter-stringed instruments. Analyses based on impulse responses and the Poisson summation formula provide an explanation to the underlying system properties.

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