Survey of the influence of the vocal tract on the clarinet sound by different signal analysis methods

Simone Geroso, Andrea Pavoni Belli Istituto Elettrotecnico Nazionale “Galileo Ferraris”, Strada delle Cacce n° 91, 10135 Torino, Italia, geroso, pavoni@ien.it

Sergio Cingolani Dipartimento Ingegneria Meccanica dell'Università Brescia, Via Branze n° 38, 25123 Brescia, Italia, sergio.cingolani@unibs.it

Marco Masoero Dipartimento Ingegneria Energetica del Politecnico di Torino, Corso Duca degli Abruzzi n° 24, 10129 Torino, Italia, masoero@polito.it

In closely musical environment the consciousness of the influence of the vocal tract on the clarinet sound is consolidated enough; indeed some clarinet players, by means of little alterations of their own vocal tract, are able to obtain various sounds, and slights corrections of tuning. In scientific environment there are some contrasting advice on this subject. The purpose of this study is to verify such influence by using various methods of signal analysis, in various registers and considering the formants of the musician vocal tract while he is playing the instrument. A comparison between analysis methods is pointed out, the results obtained in the various registers of the instrument as well as between different players is commented, carrying to the conclusion that the influence of the vocal tract on the sound is unquestionable. At the worst it is possible to say that the influence of the vocal tract is smaller in the low register of the instrument, which is called “chalumeau”.

1 Introduction

In closely musical environment of instruments like clarinet, there is the full knowledge to change considerably the timbre of own instrument modifying generically the one's vocal tract. This knowledge is describable with a series of influential factors. The musician, make use it, can modify the sound in terms of one's pleasure or characterize the sound according to the age of music that is playing. For that reason, it is not unusual, to meet particularly able musicians, that adapt the sound of their instrument modifying their vocal tract and trying, therefore, to imitate the originally sound of the instrument for which the music had been written. This is based on the historical period technique of the instrument and according to the historical and local context of the known musical interpretations of the score. At the same time, the students in the beginning with one of these instruments directly meet these difficulties: to determine the sound of their instrument in the attempt to learn “the correct position” and to adopt it to obtain “the good sound”. In truth, “the correct position” that allows anyone to obtain “the good sound” does not exist, first because “the good sound” is subjective and second because everyone must find, through a hard personal work, the one's ideal position. In scientific environment, in the relative bibliography to the musical acoustics [1, 2, 3], and in the specific of the woodwind instruments, there are some contrasting advice on this subject. In particular the references are the article of J. Backus brought back on the JASA [7] some years ago and the article brought back on the

ACUSTICA of P.G. Clinch, G.J. Troup and L. Harris [8]. All that in order to say that in scientific environment the matter still is opened. The aim of this communication is to verify the vocal tract influence on the clarinet sound, by using different methods of signal analysis. In order to make that, the sound of the instrument in the best possible conditions has been recorded; specifically for our aim, the sound signal that the musician had to play obtaining a series of sounds has been investigated, whose difference was determined exclusively from the vocal tract of the musician; finally the methods of analysis to be used and their implementation has been characterized. The conclusion is that the influence of the vocal tract on the sound is unquestionable. At the worst it is possible to say that the influence of the vocal tract is smaller in the low register of the instrument, which is called “chalumeau”.

2 Measurement of chosen signal reproduced

Initially, the recording has been performed at the Istituto Elettrotecnico Nazionale “Galileo Ferraris” of Torino, inside of the semi-anechoic room, in order to reduce strongly the background noise and the reverberating sound. A sound level meter B&K Type 2231 with microphone B&K Type 4155 is place on a support to one distance from the frontal approximately center of the instrument. The sound level meter was connected to a digital recorder DAT (TASCAM TEAC

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Forum Acusticum 2005 Budapest Geroso, Cingolani, Pavoni Belli, Masoero

Professional Division Type DA-P1), with frequency sampling equal to 48000 Hz. In order to define the signal/sound reproduced from the musician, the experience in musical field has supplied the idea: it has been devised to record notes of the clarinet executed, assuming the vocal tract “like if” one of the 5 Italians vowels had to be pronounced, without pronouncing them during the execution, therefore with stationary vocal cords. The notes executed in such way were the Mi3 of the clarinet at 146.8 Hz (more grave note of the clarinet used), and Do4 at 466.2 Hz

(corresponding respectively to Re3 and Si4). The

reason of this choice is that, in the case of Mi3 many components with elevated energetic value (fundamental and its odd harmonics) are within the acoustic filter, while for Do4, the only significant components within the filter are the fundamental and its third harmonic. Obviously the 5 vowels used are the common ones / A /, / E /, / I /, / O / and / U / without considering dialect pronunciations, inasmuch as these vocal tract are anomalous because altered from the position forced from the mouthpiece of the instrument. The measurement has followed this procedure: execution of 5 notes with vocal tract thinking to the 5 vowels, alternated from the sung execution of the same vowel, removing the instrument from the mouth but without altering the defined vocal tract from the sound of the instrument. Finally, by means of a program of editing audio, the recordings are obtained under shape of file WAV and with the same one are manipulated to extract the sections of signals used for the analyses. The signals used are sample at 44100 Hz, 16 bit and mono. About the method of measurement used, since every clarinet is different from the others and also the clarinetists, to have a sufficiently wide survey and a verification of the repeatability of the phenomenon four Maestri of clarinet have been involved; everybody has carried out the previously showed measurement.

3 Used analysis methods

The analysis methods investigated are three: two deducted from the theory of the cepstrum analysis and the other from the theory of the time-frequency analysis. These analysis methods are also used in the field of the vocal analysis for vocal acknowledgments. The practical realization of the three methods has been made in Matlab®. The first method consist of the cepstrum analysis implemented in its thoroughness in order to obtain the formants of vocal signal, that is a “liftered” spectrum of signal. The second method is deducted from the theory and the observation of the cepstrum of the signal (in particular identifying the

point t0, end of the “lifter”), but the manipulations of the signal are made in the frequency domain, filtering the signal to frequency f0=1/t0, that is a filtered spectrum of signal. The third method is deducted from the theory that define the Short Time Fourier Transform (or STFT). In our case the objective is to obtain a spectrum that evidences the envelope of considered vocal/musical signal, therefore reducing the resolution in frequency. In order to confirm the shown analysis methods, initially it has been believed to apply them to a signal of which are know the formants, that is the Italian vowel produced singing it. The vowel chosen has been the / A / since the first and the second formant are closer (respectively around to the 600 and 1100 Hz) and therefore with the possibility to evidence the effectiveness of the resolution of the methods. This test has been able to verify that the third method does not add some information to those achieved from the first two methods, therefore will not be considered. With the first method, in fact, it is possible to appreciate, with good resolution, the formants of the vocal signal and with the second to have a reference to the more exact values in frequency. This results is represented in fig. 1.

Figure 1: Sound spectrum of singing / A / with 3 different signal analysis

4 Results and comments

The diagrams obtained and showed are constituted by three curves: the thick curve represents the “liftered” spectrum of the note of clarinet by means of method 1; the outlined curve represents the filtered spectrum of the same sound with f0=1/t0 obtained by means of method 2; the thinner curve represents the “liftered” spectrum of the vocal sound, sung maintaining the vocal tract used during the note of the clarinet. Here,

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Forum Acusticum 2005 Budapest Geroso, Cingolani, Pavoni Belli, Masoero

the diagrams obtained from the measurement of the first Maestro have been brought back, but for the others, analogous results and comments has been obtained.

Figure 2: Sound spectrum of Mi3 at 146.8 Hz of the instrument and of the singing voice with 5 different

vocal tracts.

It can be noticed from these diagrams that the methods used on the “sound of the clarinet” are not be able to separate only the transfer function of the vocal tract, because the transfer function of the instrument (substantially, low-pass filter with frequency cut-off around to the 1500 Hz and exaltation of the odd harmonics of the fundamental) is much stronger and full of components. Therefore, it is necessary a careful observation of the diagrams in order to observe the differences that, in any case, are visible. These differences are more visible within the band of the low-pass filter. From these magnified diagrams it can be noticed a difference of the curves after approximately 900÷1000 Hz between the vowels / A /, / O /, / U / and/ E / or / I /; this difference is caused by the substantial difference of the correspondents formants of vowel. The vowels / E / and / I / have the second formant a lot distant regarding to the others three. This manipulate the greater harmonic components after the sixth. Furthermore the differences between the three vowels / A /, / O / and / U / can be estimated by observing the levels achieved from the curves.

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Forum Acusticum 2005 Budapest Geroso, Cingolani, Pavoni Belli, Masoero

We proceed to show the diagrams obtained from the execution of the note Do4.

Figure 3: Sound spectrum of Do4 at 466.2 Hz of the instrument and of the singing voice with 5 different

vocal tracts.

From these diagrams the influence of the vocal tract can be better seen, since the characteristics of transfer function of the instrument are always much stronger but the harmonic components are less dense, therefore they allow a better reading. All that confirms the results obtained in the article [10], which is the notes of the higher register (called “Clarino”) of the instrument are much influenced, and Do4 at 466.2 Hz is the second note of such register.

5 Conclusions

The conclusion of the present job, the influence of the vocal tract on the sound of the instrument, is unquestionable. At the worst it is possible to say that the influence of the vocal tract is smaller in the low register of the instrument, which is called “chalumeau”, and would be therefore interesting to estimate the value of impedance of the instrument in combination with this type of analysis of the corresponding sound. In this way a more direct comparison with Backus's conclusions in his article.

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References

[1] A.H. Benade, Fundamentals of Musical Acoustics, 2 ed., New York, Dover Pubblications Inc., ISBN-0-486-26484-X (1990)

[2] A. Frova, Fisica nella musica, Bologna, Ed. Zanichelli, ISBN-88-08-09012-4 (1999)

[3] S. Cingolani, R. Spagnolo edited by, Acustica musicale e architettonica, UTET, Torino, (2005)

[4] J. Brymer, Il Clarinetto, 2 ed., Padova, Franco Muzzio Editore, ISBN-88-7021-257-2 (1988)

[5] R.B. Randall, B. Tech., B.A., Frequency Analysis, 3 ed., Nærum Denmark, Brüel & Kjær, September 1987

[6] R.B. Randall, J. Hee, “Cepstrum Analysis”, Brüel & Kjær Technical Review No. 3, 1981.

[7] J. Backus, “The effect of the player's vocal tract on woodwind instrument tone”, in J. Acoust. Soc. Am., Vol. 78. No. 1. pp. 17-20. (1985)

[8] P.G. Clinch, G.J. Troup, L. Harris “The importance of vocal tract resonance in clarinet and saxophone performance. A preliminary account” in Acustica, Vol. 50. No. 4. pp. 280-284. (1982)

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