300
6 Shocks and Surprises: Refining the Elementary Model
note is pulled above or below its normal pitch centre. The basis of this technique is
the ability of the player to alter the natural resonance frequency of the lips using the
embouchure muscles, but experiments with an artificial mouth (Fréour et al. 2015)
have shown that modifications of the upstream resonance can change the pitch of
the played note even when the lip resonance frequency is held constant.
The vocal tract plays a major role in extended techniques such as sung multiphonics (Sluchin 1995; Velut et al. 2016). In the spectrograms of a sung multiphonic
shown in Fig. 5.25, it is evident that the modulation of the air flow by the vibrations
of the vocal folds during singing is not sinusoidal, since several harmonics are
visible in the frequency spectrum of the mouthpiece pressure when the lips are not
vibrating. The relative strengths of these components, and therefore the timbre of
the multiphonic created when the lips also buzz, are influenced by the resonances of
the vocal tract.
An even more spectacular illustration of the effect of windway changes on timbre
is provided by the didgeridoo (Sect. 1.1.1). A single drone note, usually the lowest
natural note of the tube, is sounded continuously; the musical interest comes from
rhythmic variations in timbre produced by changes in the vocal tract configuration,
including those required for the cyclic breathing technique that allows continuous
playing. Similar techniques are sometimes used in avant garde brass performances.
The influence of the player’s windway is much more effective in the didgeridoo
than in most conventional brass instruments because the didgeridoo does not have
a mouthpiece with a constricted throat: the lips of the player vibrate directly
against the open end of the tube, typically with diameter 30–50 mm. The impedance
peaks are not harmonically related because of the irregular bore of the tube,
and their magnitudes are typically of the same order of magnitude as the input
impedance peaks in the player’s windway (Tarnopolsky et al. 2005, 2006). The
upper resonances of the instrument are therefore very weakly coupled to the lips,
and their effect is to filter the sound in a way analogous to the creation of formants
in singing. Maxima in the input impedance of the player’s windway corresponds
to minima in the acoustic volume flow into the instrument and therefore results in
antiformants (regions of low amplitude) in the frequency spectrum of the radiated
sound.
In Chap. 3 we described how the ability of a player to buzz the lips without a
brass instrument or mouthpiece could be explained as a ‘flutter effect’, occurring
due to the coupling of two mechanical modes of the lips (Cullen et al. 2000). A
similar mechanism is responsible for driving vocal fold vibrations in voiced sound
production. An alternative interpretation of the buzzing lips phenomenon (Fletcher
and Rossing 1998) considers that the player’s mouth impedance is coupled to the
lips by the air flow. From this point of view, the destabilisation occurs because
of coupling between a mechanical mode of the lips and an acoustic mode of the
vocal tract. It seems likely that both mechanisms play some role in the buzzing lips
phenomenon.
Even where there is no deliberate use of the windway resonances in brass playing,
we have seen that a coupling between upstream and downstream exists, particularly
for high notes. It is possible that the brass player adapts the mouth geometry in order
6 Shocks and Surprises: Refining the Elementary Model
note is pulled above or below its normal pitch centre. The basis of this technique is
the ability of the player to alter the natural resonance frequency of the lips using the
embouchure muscles, but experiments with an artificial mouth (Fréour et al. 2015)
have shown that modifications of the upstream resonance can change the pitch of
the played note even when the lip resonance frequency is held constant.
The vocal tract plays a major role in extended techniques such as sung multiphonics (Sluchin 1995; Velut et al. 2016). In the spectrograms of a sung multiphonic
shown in Fig. 5.25, it is evident that the modulation of the air flow by the vibrations
of the vocal folds during singing is not sinusoidal, since several harmonics are
visible in the frequency spectrum of the mouthpiece pressure when the lips are not
vibrating. The relative strengths of these components, and therefore the timbre of
the multiphonic created when the lips also buzz, are influenced by the resonances of
the vocal tract.
An even more spectacular illustration of the effect of windway changes on timbre
is provided by the didgeridoo (Sect. 1.1.1). A single drone note, usually the lowest
natural note of the tube, is sounded continuously; the musical interest comes from
rhythmic variations in timbre produced by changes in the vocal tract configuration,
including those required for the cyclic breathing technique that allows continuous
playing. Similar techniques are sometimes used in avant garde brass performances.
The influence of the player’s windway is much more effective in the didgeridoo
than in most conventional brass instruments because the didgeridoo does not have
a mouthpiece with a constricted throat: the lips of the player vibrate directly
against the open end of the tube, typically with diameter 30–50 mm. The impedance
peaks are not harmonically related because of the irregular bore of the tube,
and their magnitudes are typically of the same order of magnitude as the input
impedance peaks in the player’s windway (Tarnopolsky et al. 2005, 2006). The
upper resonances of the instrument are therefore very weakly coupled to the lips,
and their effect is to filter the sound in a way analogous to the creation of formants
in singing. Maxima in the input impedance of the player’s windway corresponds
to minima in the acoustic volume flow into the instrument and therefore results in
antiformants (regions of low amplitude) in the frequency spectrum of the radiated
sound.
In Chap. 3 we described how the ability of a player to buzz the lips without a
brass instrument or mouthpiece could be explained as a ‘flutter effect’, occurring
due to the coupling of two mechanical modes of the lips (Cullen et al. 2000). A
similar mechanism is responsible for driving vocal fold vibrations in voiced sound
production. An alternative interpretation of the buzzing lips phenomenon (Fletcher
and Rossing 1998) considers that the player’s mouth impedance is coupled to the
lips by the air flow. From this point of view, the destabilisation occurs because
of coupling between a mechanical mode of the lips and an acoustic mode of the
vocal tract. It seems likely that both mechanisms play some role in the buzzing lips
phenomenon.
Even where there is no deliberate use of the windway resonances in brass playing,
we have seen that a coupling between upstream and downstream exists, particularly
for high notes. It is possible that the brass player adapts the mouth geometry in order