Brass instrument acoustics & language influence

The acoustics of brass instruments – Where does the influence of language come in? (Please be warned: this part is way more technical than the introductory section on my PhD research)

Although the principles of the acoustics of brass instruments are not yet fully understood, recent research in the field leads me to believe that there are certain areas of brass playing that may be affected by one’s First Language via its articulatory movements and default configuration, involving chiefly the tongue but possibly also the glottis (vocal chords) and/or alterations of the shape of the pharynx. Such unique language features are acquired subconsciously when first learning one’s First Language and this influence is thus unlikely to be noticed consciously by brass players; this may well be the reason why no research (that I know of) has been carried out in this area before.

In general, tone production on brass instruments is regarded as happening via an outward striking lip reed mechanism that excites the air column within the instrument, producing a spectrum of standing waves that are emitted from the bell at varying volumes. Bromage, Richards and Campbell (2003: 217), however, cite some sources that assume “that the lips of a brass player seem to act as both inward and outward striking reeds, so allowing the player to produce notes above, below and at the resonant frequencies of the instrument” (I roughly understand that this change (upward vs downward striking reed) happens in connection with the Bernoulli force becoming dominant (cf. Campbell & Greated 1987: 327) but I have to admit that I do not understand this completely. I believe that a better understanding this process may help to explain why some players in the studies cited later on do not seem to tune their vocal tract resonances to reach certain high notes while other players do make use of this option.). While perceived differences in articulation on brass instruments could be explained by supposing different intensities of air bursts to be expelled into the instrument due to different kinds of articulations employed by players with different First Languages, assuming that the different tongue positions for the different vowels of one’s First Language have an influence on timbre in brass playing presupposes an influence of the upstream cavity (lungs or larynx up to the lips = the vibrating reed) upon the sound waves oscillating in the downstream cavity (= the instrument). Lots of research is currently being conducted in this regard, but while the findings of published studies are not conclusive, I am convinced that there exists a margin of individual variation (influenced by one’s First Language) that will produce a different sound/timbre but which does not affect the more stable characteristics of brass instrument sound such as pitch and perceived dynamics. I will now go through a number of characteristics described in the literature on brass instrument acoustics and discuss their relation to the possibility of language influence postulated above.

Campbell and Greated (1987: 259-260) describe the following characteristics of single and double reed instruments: “In either case the reed or reeds act as a form of valve which allows the high pressure air from the player’s mouth to enter the instrument in a series of pulses which inject energy to initiate and maintain the oscillations within the tube. The oscillations of the reed are strongly influenced by the oscillations within the air column, i.e. there is a strong coupling between them.” This explains why the impedance spectrum of a brass instrument very much determines the notes that are playable with a certain valve or slide configuration. Although brass players can manipulate the vibrating frequency of their lips to select different partials available for a certain length of the instrument (extending the slide or engaging valves alter the length of the sounding air column), departing significantly from the optimal pitch pre-specified by the instrument will usually cause the lips to adjust their vibrating frequency accordingly, which may result in producing a pitch other than the originally intended one. Nevertheless, professional players can control their lip vibrations to a high extent so that they may actually alter the pitch of a desired note to some extent, although this will lead to a change of timbre.

Bertsch (1998) recorded 35 trumpet players using the same instrument and mouthpiece (although a choice of 3 different mouthpiece rims was provided) and found small differences in pitch not only among players but also intra-individually for the same note occurring twice during a played passage. Slight variation in pitch (produced on the exact same instrument) led to a change in timbre that was empirically documented by measuring the volume of individual partials contained in the recorded sound for a given note; however this is unlikely to be perceived as an intonation discrepancy even by very skilled listeners. Change of timbre as represented by varying volumes of the resonating partials has long been known as a feature that distinguishes the sound of different instruments; such transitions are results of the physics underlying the beginning of a note and a related effect applies to changes of timbre caused by playing brass instruments at different volumes and in different registers. Elliott and Bowsher (1982: 313) showed that these timbral differences are actually represented in a “complex, spiky air flow” of air pressure waveforms which they measured in a trombone mouthpiece using hot wire anemometry. (Similarly, Benade (1978: 51) describes the action of sounding a trumpet note as caused by a “state of oscillation in which several impedance maxima of the air column collaborate with the lip-valve mechanism to generate energy in a steady oscillation containing several harmonically related frequency components.”)

The central issue regarding the proposed influence of First Language on brass playing, however, is the impact of vocal tract influences on brass instrument sound/timbre. Campbell and Greated (1987: 324-325) already considered this possibility and provided some reasons why this may have been overlooked by previous research: “As long as the lungs, throat and mouth are treated purely as a means of supplying air at constant pressure behind the lips, it is difficult to see why their shape should be relevant. However, we can look on the player’s windway as effectively a second ‘brass instrument’, with the air flowing in the ‘wrong’ direction (that is, towards the lips rather than away from them)… The tubes and cavities of the windway will also have an acoustic impedance, and therefore the fluctuations in the air flow introduced by the lip vibration will cause a fluctuating pressure difference between the lungs and the mouth.” Recently, the documentation of the necessity of tuning one’s vocal tract to sound the notes within the altissimo register of saxophones, as well as investigations of the playing technique of the didgeridoo have shown that vocal tract resonances are indeed quite important for the production of wind instrument sound as well as for changes in timbre.

Wolfe, Chen and Smith (2010: 7) report the use of “[A]n artificial trombone playing system” employing “highly simplified models of lip, vocal tract and glottis” in an earlier study (Wolfe et al., 2003) which “played sharper” when used with a “high tongue configuration” “than the low tongue model when they operated on the same impedance peak of the bore. As the slide was extended, there was also a range over which the high tongue model played on a higher resonance.” They also report similar observations from skilled players: “when they lowered the tongue while playing a sustained note, and while holding all else constant, sometimes the pitch fell slightly, while sometimes it dropped to the next lower register.” Comparing such behavior to the didgeridoo, the authors state that this instrument has impedance peaks that are significantly smaller than those of brass instruments which is due to the fact that “modern lip valve instruments” “have a narrow bore near the mouthpiece, and the mouthpiece itself has a narrow constriction. Therefore, “the effects on timbre of similar articulation changes in the mouth are less striking on the brass than they are on the didjeridu.”

I did a detailed reading of two studies investigating the influence of vocal tract resonances on brass playing; these are Chen, Smith and Wolfe (2010) and Fréour and Scavone (2010). Both studies did not find that players of the brass instruments investigated (trumpet and trombone, respectively) systematically tuned their vocal tract resonances to produce certain tones and there was considerable inter-subject variation in the measured vocal tract resonances. Nevertheless, Fréour and Scavone (2010: 4) report that out of their 5 subjects, “[T]he four subjects who managed to reach the highest recorded note (F5) demonstrated SPL [sound pressure levels in dB of the upstream and downstream pressures] ratios above 3 dB for this note. Moreover, these results are consistent with a frequency range that corresponds to the second vocal-tract resonance and that was shown to be influential in supporting reed oscillation in saxophone performance.” Although the measurements reported by these authors represent an indirect way of determining vocal tract influence, it appears to me to be the case that the higher one aspires to play on a brass instrument, the more important the involvement of the vocal tract and tuning it to the correct resonance becomes. This would seem to be directly related to the petering out of impedance peaks provided by the instrument as one approaches its top range; if this assumption is correct, then it would also mean that lower notes can be produced within a large range of possible vocal tract configurations (yielding different resonances) which would not affect the possibility of sounding a note at a specific pitch but which should certainly be noticeable to skilled listeners as a difference in timbre. It is important to note, however, that there are also a number of other factors which affect timbre (in any register of the instrument) and which may enable players to produce high notes in combination with vocal tract resonances that are only approximately tuned to the desired pitch. (Fréour and Scavone (2010: 4-5) mention lip morphology and different embouchure strategies and hypothesize that they would expect subjects who demonstrate higher sound pressure levels for playing high notes to use less lip pressure (“lower lip forces”) and vice versa.)

Taking all these facts into consideration, I conclude that different tongue positions (and I believe this also includes other alterations/settings of the vocal tract) are possible while playing brass instruments (at least at the lower end of each instrument’s register) and that they lead to perceivable differences in timbre while not significantly affecting perceived pitch or even causing a different harmonic of the instrument to sound. It is therefore likely that differences in the articulatory setting and tongue movements of the different (First) Languages spoken by brass players do affect brass instrument sound if in fact they are carried over to brass playing; my initial findings seem to confirm these assumptions. All my participants will be recorded using the exact same pBone (thanks to Warwick music providing one free of charge!) and mouthpiece so that I should later on be able to compare the sound spectra produced by players from different language backgrounds.

I would like to thank Joe Wolfe and Vincent Fréour for providing valuable feedback on an earlier version of these paragraphs on brass instrument acoustics.

For references pertaining specifically to brass instrument acoustics please scroll to the bottom of this page!

 

If you’d like to find out more about the acoustics of brass instruments check out these great websites:

Brass instrument (lip reed) acoustics: An introduction
(School of Physics, University of New South Wales, Australia – also includes great pages on the acoustics of other instruments)

Vocal-tract influence in trombone performance (Vincent Fréour)

 

References:

Benade, A. H. (1978). The physics of brasses. The physics of music, Readings from Scientific American. C. M. Hutchins. San Francisco, WH Freeman & Co.: 44-55.

Bertsch, M. (1998). Studien zur Tonerzeugung auf der Trompete, University of Vienna. Ph.D. Dissertation.

Bromage, S., et al. (2003). Reproducibility and control of the embouchure of an artificial mouth for playing brass instruments. Proceedings of the Stockholm Musical Acoustics Conference.

Campbell, M. and C. Greated (1987). The musician’s guide to acoustics, Schirmer.

Elliott, S. J., and J. M. Bowsher (1982) “Regeneration in brass wind instruments.” Journal of Sound and Vibration 83, no. 2: 181-217.

Fréour, V. and G. Scavone (2010) “Vocal-tract influence in trombone performance.” Proc. 2010 ISMA.

Gardner, Joshua Thomas (2010) Ultrasonographic investigation of clarinet multiple articulation. Arizona State University. D.M.A. Dissertation.

Wolfe, J., et al. (2010). “The acoustics of wind instruments—and of the musicians who play them.” International Congress on Acoustics, Sydney.

Wolfe, J., et al. (2003). “Some effects of the player’s vocal tract and tongue on wind instrument sound.” Proc. Stockholm Music Acoust. Conf., SMAC-03, Stockholm, Sweden: 307-310.

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