Bruno Gazengel

Some aspects of tuning and clean intonation in reed instruments

Abstract The influence of the first and second resonance frequencies on tuning, timbre (or tone colour) and ease of playing is investigated for reed instruments, such as the clarinet, alto saxophone and oboe. Theoretical analyses of the effects of the reed and the player embouchure (i.e. lip position and pressure on the reed) are reviewed, as well as the consequences of inharmonicity in the resonance frequencies. This review allows us to present interesting interpretations of the numerous experiments reported here. Three kinds of results are given: (1) comparison of playing frequencies and first resonance frequencies, for several fingerings with or without open register hole, leading to the definition of a frequency independent length correction for the embouchure; (2) examination of the effect of inharmonicity of the two first resonance frequencies on both tone colour and ease of playing, the causes coming from either the player embouchure or the instrument construction; (3) comparison between theory and experiment for the inharmonicity produced by the changes in conicity in oboes, leading to an interpretation of the maker s choices. The results show how judicious use of simple tools, such as calculations or measurements of input impedance or playing data obtained using an artificial mouth, can be of help to the understanding of instrument construction and to the instrument designer.

Acoustic power flow measurement in a thermoacoustic resonator by means of laser Doppler anemometry (L.D.A.) and microphonic measurement

Abstract Acoustic power flow measurements in the resonator of a thermoacoustic refrigerator are described. The technique of measurement is based on particle velocity measurement by laser Doppler anemometry (L.D.A.) together with microphonic acoustic pressure measurement. The calibration procedure is explained and results of measurements are compared with analytical results. The L.D.A. technique permits the measurement of acoustic power flow at almost any position and for almost any working frequency in the resonator of thermoacoustic devices.

Evaluation of the performance of two acquisition and signal processing systems for measuring acoustic particle velocities in air by means of laser Doppler velocimetry

A laser Doppler velocimetry bench adapted for measuring acoustic particle velocities is used to measure sinusoidal structural velocities in order to assess the performance of two signal processing techniques, one available commercially and the other being developed in our laboratory. Considering a sinusoidal excitation signal of the vibrating structure, both techniques use frequency demodulation approaches in order to extract the instantaneous frequency of the Doppler signal which is scattered by the vibrating object and use synchronous analysis in order to estimate the amplitude and the phase of the velocities estimated by means of the frequency demodulation. The performance and limitations of the processing tools are evaluated by means of a comparison of the estimated velocities with reference values given by a laser vibrometer. Both systems show close and satisfactory performance up to 2?kHz for rms velocities higher than 1?mm?s?1.

Response of an artificially blown clarinet to different blowing pressure profiles

Using an artificial mouth with an accurate pressure control, the onset of the pressure oscillations inside the mouthpiece of a simplified clarinet is studied experimentally. Two time profiles are used for the blowing pressure: in a first set of experiments the pressure is increased at constant rates, then decreased at the same rate. In a second set of experiments the pressure rises at a constant rate and is then kept constant for an arbitrary period of time. In both cases the experiments are repeated for different increase rates. Numerical simulations using a simplified clarinet model blown with a constantly increasing mouth pressure are compared to the oscillating pressure obtained inside the mouthpiece. Both show that the beginning of the oscillations appears at a higher pressure values than the theoretical static threshold pressure, a manifestation of bifurcation delay. Experiments performed using an interrupted increase in mouth pressure show that the beginning of the oscillation occurs close to the stop in the increase of the pressure. Experimental results also highlight that the speed of the onset transient of the sound is roughly the same, independently of the duration of the increase phase of the blowing pressure.

Modeling of the subjective quality of saxophone reeds

The subjective quality of cane reeds used on saxophones or clarinets may be very different from one reed to another even though the reeds have the same shape and strength. The aim of this work is to understand the differences in the subjective quality of reeds and to explain them with objective measurements. A subjective study, involving a panel of 10 musicians, was first conducted on a set of 20 reeds of the same strength. Second, signal recordings during saxophone playing (in vivo measurements) were made of the pressures in the players mouth, in the mouthpiece and at the bell of the instrument. These measurements enable us to deduce specific parameters, such as the threshold pressure or the spectral centroid of the notes. After an analysis of the subjective and objective data (assessment of the agreement between the assessors and the main consensual differences between the reeds), correlations between the subjective and objective data were performed. To propose a model of the subjective quality, a machine learning approach was proposed using partial least-squares (PLS) regression and PLS discriminant analysis. Results show interesting performance of the model in cross validation and open the potential for an objectification of the perceived quality.

Real-Time Particle Detection and Velocity Measurement by Means of Laser Doppler Velocimetry

In this paper, the authors describe a technique for laser Doppler anemometry (LDA) data processing using two Kalman filters in order to detect the presence of particles in the probe volume and to estimate their velocities. This method turns to be suitable for designing real-time integrated velocimeters. A first Kalman filter estimates the magnitude of the Doppler signal and then compares the estimated amplitude to a threshold. A second estimator uses an extended Kalman filter (EKF) to estimate particle velocity which is supposed to be a constant. Finally, this estimator is used in order to perform air velocity measurements in a pipe

Doppler Signal Detection And Particle Time Of Flight Estimation Using Wavelet Transform For Acoustic Velocity Measurement

This paper discusses a processing technique for laser Doppler velocimetry (LDV) data, enabling to detect and localize in time domain the presence of Doppler bursts in case of acoustic excitation. A joint detection-estimation scheme based on the use of the wavelet transform (WT) realized in the time-scale domain is proposed. The performances of the detector are characterized with ROC (receiver operating characteristic) curves. Finally, the estimator performances are studied by means of Monte Carlo trials obtained from synthesized LDV signals

Estimation of saxophone reed parameters during playing.

An approach for the estimation of single reed parameters during playing, using an instrumented mouthpiece and an iterative method, is presented. Different physical models describing the reed tip movement are tested in the estimation method. The uncertainties of the sensors installed on the mouthpiece and the limits of the estimation method are studied. A tenor saxophone reed is mounted on this mouthpiece connected to a cylinder, played by a musician, and characterized at different dynamic levels. Results show that the method can be used to estimate the reed parameters with a small error for low and medium sound levels (piano and mezzoforte dynamic levels). The analysis reveals that the complexity of the physical model describing the reed behavior must increase with dynamic levels. For medium level dynamics, the most relevant physical model assumes that the reed is an oscillator with non-linear stiffness and damping, the effect of mass (inertia) being very small.

A new impedance tube for large frequency band measurement of absorbing materials

The standard two microphones technique does not allow the measurement of absorbing materials characteristics at low frequency. Moreover, to cover a range from 100 to 6000 Hz two experiments have to be done with two different sample diameters. By using a sensor with a known volume velocity source developed by the LAUM together with the CTTM, it is demonstrated that the impedance can be obtained from 10 to 6000 Hz by performing only one measurement with a single material sample. Results showing the behaviour of some materials at low frequency are presented. On the other hand a comparison is done with classical Kundt tube results.

Digital Calibration Procedure for Laser Doppler Velocimetry in Acoustics

This paper propose a digital calibration procedure for errors compensation of the output signals of an analogical quadrature demodulation (QD) hardware. This kind of device is used for laser Doppler velocimetry (LDV) measurements in acoustics. The method developed is based on the use of a maximum likelihood estimator (MLE) in order to estimate the amplitudes, the tension offsets, and the phase shift of two quadrature signals. Such a technique provides a good and a simple way for QD calibration.