15,355 research outputs found
Nonlinear modes of clarinet-like musical instruments
The concept of nonlinear modes is applied in order to analyze the behavior of
a model of woodwind reed instruments. Using a modal expansion of the impedance
of the instrument, and by projecting the equation for the acoustic pressure on
the normal modes of the air column, a system of second order ordinary
differential equations is obtained. The equations are coupled through the
nonlinear relation describing the volume flow of air through the reed channel
in response to the pressure difference across the reed. The system is treated
using an amplitude-phase formulation for nonlinear modes, where the frequency
and damping functions, as well as the invariant manifolds in the phase space,
are unknowns to be determined. The formulation gives, without explicit
integration of the underlying ordinary differential equation, access to the
transient, the limit cycle, its period and stability. The process is
illustrated for a model reduced to three normal modes of the air column
Optimal control theory : a method for the design of wind instruments
It has been asserted previously by the author that optimal control theory can
be a valuable framework for theoretical studies about the shape that a wind
instrument should have in order to satisfy some optimization criterion, inside
a fairly general class. The purpose of the present work is to develop this new
approach with a look at a specific criterion to be optimized. In this setting,
the Webster horn equation is regarded as a controlled dynamical equation in the
space variable. Pressure is the state, the control being made of two parts: one
variable part, the inside diameter of the duct and one constant part, the
weights of the elementary time-harmonic components of the velocity potential.
Then one looks for a control that optimizes a criterion related to the
definition of an {oscillation regime} as the cooperation of several natural
modes of vibration with the excitation, the {playing frequency} being the one
that maximizes the total generation of energy, as exposed by A.H. Benade,
following H. Bouasse. At the same time the relevance of this criterion is
questioned with the simulation results.Comment: To appear in Acta Acustica united with Acustica, 201
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Developing and evaluating a hybrid wind instrument
A hybrid wind instrument generates self-sustained sounds via a real-time interaction between a computed excitation model (such as the physical model of human lips interacting with a mouthpiece) and a real acoustic resonator. Attempts to produce a hybrid instrument have so far fallen short, in terms of both the accuracy and the variation in the sound produced. The principal reason for the failings of previous hybrid instruments is the actuator which, controlled by the excitation model, introduces a fluctuating component into the air flow injected into the resonator. In the present paper, the possibility of using a loudspeaker to supply the calculated excitation signal is evaluated. A theoretical study has facilitated the modeling of the loudspeaker-resonator system and the design of a feedback and feedforward filter to successfully compensate for the presence of the loudspeaker. The resulting self-sustained sounds are evaluated by a mapping of their sound descriptors to the input parameters of the physical model of the embouchure, both for sustained and attack sounds. Results are compared with simulations. The largely coherent functioning confirms the usefulness of the device in both musical and research contexts
Digital waveguide modeling for wind instruments: building a state-space representation based on the Webster-Lokshin model
This paper deals with digital waveguide modeling of wind instruments. It presents the application of state-space representations for the refined acoustic model of Webster-Lokshin. This acoustic model describes the propagation of longitudinal waves in axisymmetric acoustic pipes with a varying cross-section, visco-thermal losses at the walls, and without assuming planar or spherical waves. Moreover, three types of discontinuities of the shape can be taken into account (radius, slope and curvature).
The purpose of this work is to build low-cost digital simulations in the time domain based on the Webster-Lokshin model. First, decomposing a resonator into independent elementary parts and isolating delay operators lead to a Kelly-Lochbaum network of input/output systems and delays. Second, for a systematic assembling of elements, their state-space representations are derived in discrete time. Then, standard tools of automatic control are used to reduce the complexity of digital simulations in the time domain. The method is applied to a real trombone, and results of simulations are presented and compared with measurements. This method seems to be a promising approach in term of modularity, complexity of calculation and accuracy, for any acoustic resonators based on tubes
How do clarinet players adjust the resonances of their vocal tracts for different playing effects
In a simple model, the reed of the clarinet is mechanically loaded by the
series combination of the acoustical impedances of the instrument itself and of
the player's vocal tract. Here we measure the complex impedance spectrum of
players' tracts using an impedance head adapted to fit inside a clarinet
mouthpiece. A direct current shunt with high acoustical resistance allows
players to blow normally, so the players can simulate the tract condition under
playing conditions. The reproducibility of the results suggest that the
players' "muscle memory" is reliable for this task. Most players use a single,
highly stable vocal tract configuration over most of the playing range, except
for the altissimo register. However, this 'normal' configuration varies
substantially among musicians. All musicians change the configuration, often
drastically for "special effects'' such as glissandi and slurs: the tongue is
lowered and the impedance magnitude reduced when the player intends to lower
the pitch or to slur downwards, and vice versa
Oscillation threshold of a clarinet model: a numerical continuation approach
This paper focuses on the oscillation threshold of single reed instruments.
Several characteristics such as blowing pressure at threshold, regime
selection, and playing frequency are known to change radically when taking into
account the reed dynamics and the flow induced by the reed motion. Previous
works have shown interesting tendencies, using analytical expressions with
simplified models. In the present study, a more elaborated physical model is
considered. The influence of several parameters, depending on the reed
properties, the design of the instrument or the control operated by the player,
are studied. Previous results on the influence of the reed resonance frequency
are confirmed. New results concerning the simultaneous influence of two model
parameters on oscillation threshold, regime selection and playing frequency are
presented and discussed. The authors use a numerical continuation approach.
Numerical continuation consists in following a given solution of a set of
equations when a parameter varies. Considering the instrument as a dynamical
system, the oscillation threshold problem is formulated as a path following of
Hopf bifurcations, generalizing the usual approach of the characteristic
equation, as used in previous works. The proposed numerical approach proves to
be useful for the study of musical instruments. It is complementary to
analytical analysis and direct time-domain or frequency-domain simulations
since it allows to derive information that is hardly reachable through
simulation, without the approximations needed for analytical approach
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