Alex Z Tarnopolsky

Acoustics of the avian vocal tract

The general principles underlying the acoustic performance of the avian vocal tract are examined both theoretically and experimentally. The formantresonances produced both by the total vocal tract and by the bronchial tubes are evaluated quantitatively, and their dependence upon anatomical parameters is investigated. A simplified cylindrical model for the beak is examined theoretically, and experimental results are presented that confirm the predictions of the theory for this model. A similar theoretical and experimental investigation using a more realistic conical beak model is also reported, and behaves as predicted. Finally a theoretical study of the effect of mouth volume, as influenced by tongue position, is integrated with these other studies to produce a complete analysis. The implications of these studies for understanding the acoustical behavior of avian vocal tracts are discussed.

Blowing pressure, power, and spectrum in trumpet playing

Measurements of sound output as a function of blowing pressure are reported for a group of experienced trumpet players. The study identifies several common features, namely (1) a threshold blowing pressure approximately proportional to the frequency of the note being played, (2) an extended region in which the sound output rises by about 15 dB for each doubling of blowing pressure, and (3) a saturation region in which sound output rises by only about 3 dB for a doubling of blowing pressure. Some players are able to blow with maximum pressures as high as 25 kPa, which is significantly greater than normal systolic blood pressure. A simple theory is presented that provides a physical explanation for the acoustical behavior, but a detailed treatment requires solution of the nonlinear coupled equations both for the lip-valve mechanism and for nonlinear wave propagation in the instrument tube. Frequency analysis of the sound shows a basic spectral envelope determined by the resonance properties of the mouthpiece cup and the radiation behavior of the bell, supplemented by an extension to increasingly high frequencies as the blowing pressure is increased. This high-frequency behavior can be attributed to nonlinear wavefront steepening during sound propagation along the cylindrical bore of the instrument.

Acoustics: the vocal tract and the sound of a didgeridoo.

The Australian didgeridoo (or yidaki in the Yolngu language of northern Australia) is a simple musical instrument that, at the lips of an experienced player, is capable of a spectacular variety of timbres — considerably greater than those that can be coaxed from orchestral instruments, for example. To understand this phenomenon, we simultaneously measured the sound produced by the didgeridoo and the acoustic impedance of the players vocal tract. We find that the maxima in the envelope of the sound spectrum are associated with minima in the impedance of the vocal tract, as measured just inside the lips. This acoustic effect is similar to the production of vowel sounds made during human speech or singing, although the mechanism is different, and leads to the surprising conclusion that experienced players are subconsciously using their glottis to accentuate the instruments tonal variation.

Acoustic impedance measurements—correction for probe geometry mismatch

The effect of evanescent mode generation, due to geometrical mismatch, in acoustic impedance measurements is investigated. The particular geometry considered is that of a impedance probe with an annular flow port and a central microphone, but the techniques are applicable to other geometries. It is found that the imaginary part of the measured impedance error is proportional to frequency, and that the sign of the error is positive for measurements made on tubes with diameter much larger than that of the inlet port, but negative for tubes with diameter close to that of the inlet. The result is a distortion of the measured frequencies of the impedance minima of the duct while the maxima are largely unaffected. There is, in addition, a real resistive component to the error that varies approximately as the square root of the frequency. Experiment confirms the results of the analysis and calculations, and a calibration procedure is proposed that allows impedance probes that have been calibrated on a semi-infinite tube of one diameter to be employed for measurements on components with an inlet duct of some very different diameter.

The Vocal Tract and the Sound of a Didgeridoo

The Australian didgeridoo (or yidaki in the Yolngu language of northern Australia) is a simple musical instrument that, at the lips of an experienced player, is capable of a spectacular variety of timbres — considerably greater than those that can be coaxed from orchestral instruments, for example. To understand this phenomenon, we simultaneously measured the sound produced by the didgeridoo and the acoustic impedance of the players vocal tract. We find that the maxima in the envelope of the sound spectrum are associated with minima in the impedance of the vocal tract, as measured just inside the lips. This acoustic effect is similar to the production of vowel sounds made during human speech or singing, although the mechanism is different, and leads to the surprising conclusion that experienced players are subconsciously using their glottis to accentuate the instruments tonal variation.

Vocal tract resonances and the sound of the Australian didjeridu (yidaki) II. Theory

The didjeridu (didgeridoo) or yidaki of the Australian Aboriginal people consists of the narrow trunk of a small Eucalypt tree that has been hollowed out by the action of termites, cut to a length of about 1.5 m, smoothed, and decorated. It is lip-blown like a trumpet and produces a simple drone in the frequency range 55 to 80 Hz. Interest arises from the fact that a skilled player can make a very wide variety of sounds with formants rather like those of human vowels, and can also produce additional complex sounds by adding vocalization. An outline is given of the way in which the whole system can be analyzed using the harmonic-balance technique, but a simpler approach with lip motion assumed shows easily that upper harmonics of the drone with frequencies lying close to impedance maxima of the vocal tract are suppressed, so that formant bands appear near impedance minima of the vocal tract. This agrees with experimental findings. Simultaneous vibration of the players lips and vocal folds is shown to generate multiple sum and difference tones, and can be used to produce subharmonics of the drone. A brief discussion is given of player preference of particular bore profiles.

The vocal tract and the sound of a didgeridoo: Acoustics

The Australian didgeridoo (or yidaki in the Yolngu language of northern Australia) is a simple musical instrument that, at the lips of an experienced player, is capable of a spectacular variety of timbres — considerably greater than those that can be coaxed from orchestral instruments, for example. To understand this phenomenon, we simultaneously measured the sound produced by the didgeridoo and the acoustic impedance of the players vocal tract. We find that the maxima in the envelope of the sound spectrum are associated with minima in the impedance of the vocal tract, as measured just inside the lips. This acoustic effect is similar to the production of vowel sounds made during human speech or singing, although the mechanism is different, and leads to the surprising conclusion that experienced players are subconsciously using their glottis to accentuate the instruments tonal variation.