Evaluating the suitability of acoustical measurement techniques and psychophysical testing for studying the consistency of musical wind instrument manufacturing

Musicians often claim to be able to discern differences in the playing properties of musical wind instruments that have been manufactured in exactly the same way. These differences are most likely due to disparities in bore profile or in the positioning and sealing of any valves or side holes. In this paper, the suitability of acoustic pulse reflectometry and a capillary-based impedance measurement technique for detecting differences between instruments of the same model is explored through measurements on two low-cost, mass-produced trumpets. Differences in the measured bore profiles of the two instruments are reported, with the largest deviation caused by the presence of a leak in the third valve of one of the trumpets. Differences in input impedance measurements made on the two instruments are also noted, with the main cause shown to be the leaky valve. Controlled playing tests are carried out using the same two trumpets in order to evaluate the effectiveness of psychophysical testing in establishing whether there are perceptible differences in the playing properties of nominally identical wind instruments. A semi-professional musician is proved to be able to discriminate between the trumpets whereas an amateur player is shown to be unable to do the same.     

Study of the brightness of trumpet tones

This study focuses on a particular attribute of trumpet tones, the brightness, and on the physical characteristics of the instrument thought to govern its magnitude. On the one hand, an objective study was carried out with input impedance measurements, and, on the other hand, a subjective study with hearing tests and a panel of subjects. To create a set of different trumpets a variable depth mouthpiece was developed whose depth can be easily and continuously adjusted from "deep" to "shallow." Using this mouthpiece and the same trumpet, several instruments were generated which may be played in three ways: (i) by a musician, (ii) by an artificial mouth, and (iii) using physical modeling simulations. The influence of the depth of the mouthpiece on the perception of the trumpet's tones was investigated, and the ability of a musician, the artificial mouth, or physical modeling simulations to demonstrate perceptively noticeable differences was assessed. Physical characteristics extracted from the impedance curves are finally proposed to explain the brightness of trumpet tones. As a result, the physical modeling simulations now seem to be mature enough to exhibit coherent and subtle perceptual differences between tones. This opens the door to virtual acoustics for instrument makers.     

Trumpet with near-perfect harmonicity: design and acoustic results

This paper presents a mathematical design methodology for determining the shape of a trumpet air column that has near-perfect harmonicity, whose components are discontinuity-free, and whose input impedance peak heights are balanced over the playing range. The simulation model employed assumes linear wave propagation and uses cylindrical element discretization with a plane wave approximation. Acoustic measurements are made using a test set-up with an estimated relative measurement error of ±3 cents. Comparisons of measured results are given for the presented design (Macaluso trumpet) and the same trumpet air column with the bell replaced by a commercially used generic trumpet bell of unknown shape (Generic trumpet). For acoustic resonance modes 2-13 (233-1515 Hz), the measured root-mean-square (rms) harmonicity deviation is 5 cents for the Macaluso trumpet, whereas it is 18 cents for the Generic trumpet. However, considering the estimated measurement uncertainty, each of those deviations is somewhat over-stated. For that same range of resonances, the rms deviation between measured and calculated resonance frequencies for the Macaluso trumpet is 3 cents, thus validating the presented simulation model and equations.     

Comparative measurements of loudspeakers in a listening situation

Comparison of loudspeakers is a major concern during design or product selection. There are several standards for the measurement of loudspeaker characteristics, but none of them provides hints for a rigorous comparison between devices. In this study, different ways of evaluating acoustical dissimilarity between loudspeakers were compared. Several methods of signal analysis were used, and for each method a metric evaluating the dissimilarity between two signals was defined. The correlation between the different dissimilarity evaluations over a significant panel of loudspeakers led to identified classes of measurements. A specific aspect of this work is that measurements were performed in a standard listening environment, rather than in an anechoic or reverberant one. It allowed the use of the recorded signals for a simple listening test, providing a perceptual metric which was compared to the acoustical ones. It also allowed the introduction of auditory models in the computation of some acoustical metrics, so defining a new class of measurements which gave results close to the perceptual ones.     

Objective assessment of the sound paths through earmuff components

This paper proposes an objective measurement methodology to assess the sound transmission paths through various earmuff components (cup, cushion, back-plate, foam insert, silicone flesh) and estimate the vibroacoustic couplings between them. The measurement methodology is applied to two different commercial earmuffs. For each Hearing Protection Device (HPD), the different sound paths are assessed, by analyzing separately the vibroacoustic behavior of each HPD component. In particular, the Insertion Loss (IL) of the lateral walls of the cushion is assessed, with and without pumping motion. The effect of the coupling between the different parts is also investigated from the comparison of the separate components with the complete earmuff. As shown in past studies, results confirm that the acoustical behavior of an earmuff is governed by the pumping motion and air leaks at low frequency and by the sound path through the cup and the cavity resonances at high frequency. However, at mid frequency, new counter-intuitive results are revealed. It is found that earmuffs do not behave as their weakest element, but rather as the one which has the highest attenuation. It is also observed that the foam insert can also decrease the IL. Complementary tests using other absorbing materials show that this effect could mainly be attributed to the absorption behaviors of each material at medium frequencies.     

Finite element formulations for acoustical radiation

Finite and infinite element techniques are applied to linear acoustical problems involving infinite anechoic boundaries. Theory is presented for a simple one dimensional model based on Webster's horn equation. Results are then presented both for the one dimensional model and for two axisymmetric test cases. Comparisons with exact solutions indicate that both the infinite element and wave envelope schemes are effective in correctly predicting the near field. The wave envelope scheme is also shown to be capable of resolving the far field radiation pattern.     

Electron-phonon interactions in bct white tin

The electron-phonon interactions are evaluated exactly over the actual shape of the atomic polyhedron as well as the lattice polyhedron of diatomic white tin by making use of simple coordinate axes transformations and crystal symmetry. It is shown that the expressions for the interference factor,S(q, t) of the atomic polyhedron are complex while those for the lattice polyhedron are real and the reciprocal lattice vectors derived from the former do not correspond to those derived either from the latter or from x-ray structure factors. By comparing these expressions with each other as well as with those obtained by approximating these polyhedra by an ellipsoid of equivalent volume, apparent differences between the interference factors of atomic and lattice polyhedra, consequent ambiguity regarding the shape and size of the first Brillouin zone of white tin, validity of the Wigner-Seitz approximation for a diatomic lattice and the manner in which the electron-phonon interactions contribute to acoustical and optical modes of vibration are discussed.     

Speech related acoustical parameters in classrooms and their relationships

A survey on the speech related acoustical parameters in the Hong Kong classrooms having standardized architectural layouts is carried out in the present study. Results suggest that these acoustical parameters are highly correlated with each other even across different octave bands. It is also found that the relationships between parameters of different kinds do not depend on the frequency bands. Besides, the present results indicate that the sound pulse decay inside a not very reverberant classroom consists of an initial fast decay, leading to deviations of the field survey results from those predicted by the exponential decay under the uniform sound energy decay assumption. It is believed that the strong correlations between the various speech related acoustical parameters and the regression information obtained in the present study can help the estimation of the speech quality of the classrooms in the design stage.     

Inversion of acoustic mode coupling coefficient matrix

It is found that the normal mode amplitude time series consist of multi-frequency component by analyzing the structure of acoustical signal when internal wave propagation exists, and each frequency is the product of internal wave speed and the normal mode wave number difference between acoustical receivers and source. The amplitude of each component is proportional to the acoustic mode coupling coefficient. The structure of the normal mode coefficient time series is still complex even the internal waves do not reshape when they propagate from the acoustical receivers to the source. A method is presented to compute the AMCCM by the feature of IWs' motion and the relation between the AMCCM and the acoustical signal fluctuation amplitude. The IWs data measured in the 2001 Asia experiment (ASIAEX2001) is used to check the accuracy of this method by numerical simulation. It is show that the method is accurate to compute the AMCCM.     

Measurement of the flow and its vibration in Japanese traditional bamboo flute using the dynamic PIV

All wind instruments produce sound due to the vibration of air inside of the instrument. In the case of a trumpet or a clarinet, the mouth or a reed helps to generate variable tones. In the case of a flute, there is no mechanical vibration. Additional detail about the flow and the sound vibration inside and outside of the flute are investigated in order to understand the mechanism of the wind instrument and to aid in the manufacture of quality instruments. In this report, a traditional Japanese bamboo flute was investigated experimentally. The dynamic PIV technique was applied to measure the vibration. Two kinds of experiments were performed. Argon-gas flow containing an oil mist as tracer particles both inside and outside the bamboo flute was measured using a high frequency pulse laser. The periodical flow near a hole of the bamboo flute was successfully measured. The flow was found to go into and out from the flute and the balance of a mass flow rate and the averaged velocity were almost zero at the hole. Then, the flow in the bamboo flute was visualized when a human played the instrument, using a CW-laser and water-mist as the tracer. It was discovered that the two instructors had unique methods for playing the flue instrument.     

Reciprocal maximum-length sequence pairs for acoustical dual source measurements

In this paper we propose and demonstrate a method to obtain simultaneous dual source-receiver impulse responses in acoustical systems using binary maximum-length sequences (MLS). A binary MLS and its reversed-order sequence form a reciprocal MLS pair. Their correlation property includes a two-valued "pulse-like" autocorrelation function and a relatively smaller-valued cross-correlation function. This unique property, along with other number-theory properties, makes the reciprocal MLS pair suitable for simultaneous dual source cross-correlation measurements. In the measurement of a dual source system, each of the reciprocal MLS pairs simultaneously excite one of two separate sources, one or several receiver signals cross-correlate in turn with each of the MLS pairs, resulting in impulse responses associated with two separate sources. The proposed method is particularly valuable for system identification tasks with multiple sound/vibration sources and receivers that have to be accomplished in a limited time period. A fast algorithm called a fast MLS transform is exploited for the cross-correlation. In this paper we propose a fast MLS transform pair for the reciprocal MLS pairs. Its efficiency lies in the requirement of one single permutation matrix for a pair of two fast MLS transforms. Its feasibility and usefulness in the acoustical measurements are demonstrated using experimental results.     

A methodological and preliminary study on the acoustic effect of a trumpet player's vocal tract

A methodological study is presented to examine the acoustic role of the vocal tract in playing the trumpet. Preliminary results obtained for one professional player are also shown to demonstrate the effectiveness of the method. Images of the vocal tract with a resolution of 0.5 mm (2 mm in thickness) were recorded with magnetic resonance imaging to observe the tongue posture and estimate the vocal-tract area function during actual performance. The input impedance was then calculated for the player's air column including both the supra- and subglottal tracts using an acoustic tube model including the effect of wall losses. Finally, a time-domain blowing simulation by Adachi and Sato [J. Acoust. Soc. Am. 99, 1200-1209 (1996)] was performed with a model of the lips. In this simulation, the oscillating frequency of the lips was slightly affected by using different shapes of the vocal tract measured for the player. In particular, when the natural frequency of the lips was gradually increased, the transition to the higher mode occurred at different frequencies for different vocal-tract shapes. Furthermore, simulation results showed that the minimum blowing pressure required to attain the lip oscillation can be reduced by adjusting the vocal-tract shape properly.     

Do trumpet players tune resonances of the vocal tract?

The acoustic impedance spectrum was measured in the mouths of seven trumpeters while they played normal notes and while they practiced "bending" the pitch below or above the normal value. The peaks in vocal tract impedance usually had magnitudes rather smaller than those of the bore of the trumpet. Over the range measured, none of the trumpeters showed systematic tuning of the resonances of the vocal tract. However, all players commented that the presence of the impedance head in the mouth prevented them from playing the very highest notes of which they were normally capable. It is therefore possible that these players might use either resonance tuning or perhaps very high impedance magnitudes for some notes beyond the measured range. The observed lack of tuning contrasts with measurements for the saxophone which, like the trumpet, has weak resonances in the third and fourth octaves. Saxophonists are only able to play the highest range by tuning resonances of the vocal tract, so that the series impedance has a very strong peak at a frequency near that of the desired note. This difference is explained by the greater control that the trumpet player has over the natural frequency of the vibrating valve.     

Comparison of various modes of presenting sentence materials in tests of speech perception in noise

This study compares alternative modes of presenting sentences in testing situations where noise is employed and where the required response is only one word in the sentence. The purpose is to establish the extent to which contextual information is transmitted to the listener in the following four presentation modes: (1) acoustical presentation of the test word under noise and written presentation of the rest of the sentence (mode W); (2) acoustical presentation of sentence and test word under uniform noise (mode A); (3) superposition of the previous two modes (mode B); and (4) acoustical presentation of the test word under noise in one ear, immediately following the presentation of the rest of the sentence without noise in the other ear (mode C). Modes B and C are found to be essentially equivalent to mode W. When mode A is used, the intelligibility of the test word is substantially lower than with mode W, especially at low signal-to-noise (S/N) ratios. These results are particularly relevant to testing situations where the primary intent is to assess the utilization of contextual information in perceiving speech.     

Investigating the consistency of woodwind instrument manufacturing by comparing five nominally identical oboes

For large-scale woodwind instrument makers, producing instruments with exactly the same playing characteristics is a constant aim. This paper explores manufacturing consistency by comparing five Howarth S10 student model oboes. Psychophysical testing involving nine musicians is carried out to investigate perceived differences in the playing properties of the two Howarth oboes believed to be most dissimilar. Further testing, involving one musician and combinations of the five oboes, provides information regarding the relative playabilities of the instruments at specific pitches. Meanwhile, input impedance measurements are made on the five oboes for fingerings throughout the playing range and their bore profiles are measured. The main findings are (1) the two instruments used in the preliminary psychophysical testing are perceived as identical by most of the musicians, although differences are identified by two players when playing the note F6 and by one player when playing in the lowest register, (2) a variation in the playability of F6 across the five oboes is due to differences in the elevation of the C key, and (3) variations in the playing properties in the lowest register are related to input impedance differences,which, in turn, appear to be at least partly due to bore profile differences.     

Occluded-ear simulator with variable acoustic properties.

Ear simulators were designed to replicate acoustical characteristics of the average adult ear. Due to variability of ear-canal geometry and eardrum impedance among individuals, the possibility of any one person exhibiting such "average" characteristics--especially if that person is a child and/or has a conductive pathology--is remote. Thus, ear simulators have been of only peripheral value when prescribing a hearing aid (a high output impedance device) to fit the acoustical requirements of a particular patient. Reported herein is development of a programmable artificial ear (PAE) that can account for individual differences in ear-canal geometry and eardrum impedance. It consists of a 2.0-cc coupler, microphone, amplifier, computer, PAE code, and a computer card and/or software for digitization and Fourier transformation. Required input data includes ear-canal dimensions, eardrum impedance, and output impedance of the hearing aid being tested. Sound-pressure recordings produced in the 2.0-cc coupler by the hearing aid are adjusted by the computer to what they would have been had the recordings been made at the eardrum of a particular patient wearing the same hearing aid. Good agreement was observed between experiment and theory for one test case involving a totally occluding miniature earphone.     

Experimentally based description of harp plucking

This paper describes an experimental study of string plucking for the classical harp. Its goal is to characterize the playing parameters that play the most important roles in expressivity, and in the way harp players recognize each other, even on isolated notes--what we call the "acoustical signature" of each player. We have designed a specific experimental setup using a high-speed camera that tracks some markers on the fingers and on the string. This provides accurate three-dimensional positioning of the finger and of the string throughout the plucking action, in different musical contexts. From measurements of ten harp players, combined with measurements of the soundboard vibrations, we extract a set of parameters that finely control the initial conditions of the string's free oscillations. Results indicate that these initial conditions are typically a complex mix of displacement and velocity, with additional rotation. Although remarkably reproducible by a single player--and the more so for professional players--we observe that some of these control parameters vary significantly from one player to another.     

A scale value for the balance inside a historical opera house

In the framework of opera house acoustics, the term "balance" refers to the acoustical competition between the singer on the stage and the orchestra in the pit. The mechanism allowing the operatic singers to be heard over the orchestra has to do with their skill in enhancing the vocal emission by a peculiar use of the formant frequencies. This vital factor is sensed by the listeners and, apart from the obvious sound power ratio of the stage and the pit sources, is the main cue that helps to formulate a subjective impression of the balance. To achieve its objective qualification, two calibrated sound sources can be placed on the stage and in the pit, respectively, and their sound level difference is measured at the listeners' seats. The scope of this work is to investigate the relationship between the subjective impression and the objective indicator of the balance and to develop a scale value for the parameter in the case of a historical opera house. For this scope a set of acoustical data from the Teatro Comunale in Ferrara will be used to create synthetic sound fields with controlled conditions of the balance between the stage and the pit. This methodology employs an anechoic piece for soprano (with piano accompaniment) and is implemented in a dead room equipped with an acoustical rendering system. The sound fields are used to investigate the appropriate balance values by means of listening tests. The results of the scaling exercise show that a suitable range of values can be extracted and that the sound from the stage and the pit is perceived as balanced when the loudness difference between the two is comprised within -2.0 dBA and +2.3 dBA.     

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 airway. Here we measure the complex impedance spectrum of players' airways 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.