412
9 Looking Back and Looking Forward
excitation
loudspeaker
acoustic
termination
mouthpiece
reference
control
loudspeaker
power
amplifier
DSP
analog separator
−
+
DSP board
0
Fig. 9.10 Experimental setup for active controlled flute (Guérard and Boutillon 1998)
of an infinitely long pipe. Additional digital filters in the control software were used
to reproduce the reflection functions corresponding to different patterns of open and
closed holes on a real flute; in this way the flute could be ‘played’ over a pitch range
of an octave.
Applications of active control methods in musical acoustics have been mainly
confined to stringed and percussion instruments (Griffin et al. 2003; Boutin et
al. 2015a; Benacchio et al. 2016), although the single-mode Helmholtz resonator
designed by Chen and Weinreich (1996) to study the phase behaviour of the lips
of trumpeters (see Sect. 5.2.1) could be considered as the first actively controlled
brass instrument. The use of modal active control to change the playing properties
of a simplified bass clarinet without holes has been described by Meurisse et al.
(2015a). In this case the controlling feedback loop was provided by a single wallmounted microphone and loudspeaker near the open end of the tube. By measuring
and adjusting the transfer function between the speaker and microphone of the
control setup, it was possible to modify the input impedance and the radiated sound
of the instrument.
Improving the sound quality and playability of a brass instrument through the
use of active control is an intriguing possibility, but its practical implementation is
currently limited by technical problems such as latency in the control loop. One
important application of active control to solve a common problem with brass
instrument mutes has been described by Meurisse et al. (2015b). In Sect. 4.5.2 it
was noted that when a straight mute is used with a brass instrument, the frequencies
of its lowest impedance peaks are slightly modified, and an extra ‘parasitic’ peak
appears. This peak affects the playability of the instrument, making some lower
notes difficult or impossible to sound quietly (Velut et al. 2017b).
In the trombone mute with active control illustrated in Fig. 9.11, a small
microphone inside the mute cavity senses the internal pressure. This signal is sent
to the control software, which supplies a correcting signal with modified gain and
phase to an internal loudspeaker. The experimental results in Fig. 9.12 show that
with a phase inversion ( = π ) and a gain of 2 in the control loop, the parasitic
peak can be almost completely suppressed, leading to a marked improvement in the
playability of the affected note (in this case the pedal note B 1).
9 Looking Back and Looking Forward
excitation
loudspeaker
acoustic
termination
mouthpiece
reference
control
loudspeaker
power
amplifier
DSP
analog separator
−
+
DSP board
0
Fig. 9.10 Experimental setup for active controlled flute (Guérard and Boutillon 1998)
of an infinitely long pipe. Additional digital filters in the control software were used
to reproduce the reflection functions corresponding to different patterns of open and
closed holes on a real flute; in this way the flute could be ‘played’ over a pitch range
of an octave.
Applications of active control methods in musical acoustics have been mainly
confined to stringed and percussion instruments (Griffin et al. 2003; Boutin et
al. 2015a; Benacchio et al. 2016), although the single-mode Helmholtz resonator
designed by Chen and Weinreich (1996) to study the phase behaviour of the lips
of trumpeters (see Sect. 5.2.1) could be considered as the first actively controlled
brass instrument. The use of modal active control to change the playing properties
of a simplified bass clarinet without holes has been described by Meurisse et al.
(2015a). In this case the controlling feedback loop was provided by a single wallmounted microphone and loudspeaker near the open end of the tube. By measuring
and adjusting the transfer function between the speaker and microphone of the
control setup, it was possible to modify the input impedance and the radiated sound
of the instrument.
Improving the sound quality and playability of a brass instrument through the
use of active control is an intriguing possibility, but its practical implementation is
currently limited by technical problems such as latency in the control loop. One
important application of active control to solve a common problem with brass
instrument mutes has been described by Meurisse et al. (2015b). In Sect. 4.5.2 it
was noted that when a straight mute is used with a brass instrument, the frequencies
of its lowest impedance peaks are slightly modified, and an extra ‘parasitic’ peak
appears. This peak affects the playability of the instrument, making some lower
notes difficult or impossible to sound quietly (Velut et al. 2017b).
In the trombone mute with active control illustrated in Fig. 9.11, a small
microphone inside the mute cavity senses the internal pressure. This signal is sent
to the control software, which supplies a correcting signal with modified gain and
phase to an internal loudspeaker. The experimental results in Fig. 9.12 show that
with a phase inversion ( = π ) and a gain of 2 in the control loop, the parasitic
peak can be almost completely suppressed, leading to a marked improvement in the
playability of the affected note (in this case the pedal note B 1).