Trombone Synthesis by Model and Measurement

A physics-based synthesis model of a trombone is developed using filter elements that are both theoretically-based and estimatedfrom measurement. The model consists of two trombone instrument transfer functions: one at the position of the mouthpieceenabling coupling to a lip-valve model and one at the outside of the bell for sound production. The focus of this work is onextending a previously presented measurement technique used to obtain acoustic characterizations of waveguide elements forcylindrical and conical elements, with further development allowing for the estimation of the flared trombone bell reflection andtransmission functions for which no one-parameter traveling wave solution exists. A one-dimensional bell model is developedproviding an approximate theoretical expectation to which estimation results may be compared. Dynamic trombone modelelements, such as those dependent on the bore length, are theoretically and parametrically modeled. As a result, the trombonemodel focuses on accuracy, interactivity, and efficiency, making it suitable for a number of real-time computer music applications

The optimisation of brass instruments to include wall vibration effects

This thesis focuses on the design optimisation of a brass instrument. The bore profile of such an instrument is known to be the primary influence on the sound of the instrument as it directly controls the shape of the air-column contained within the instruments' walls. It has long been claimed, however, that other factors, such as the wall material and wall vibrations, are also significant, although to a lesser degree. In recent years, it has been proven that wall vibrations do indeed have an audible effect on the sound (Moore et al 2005, Kausel et al 2007, Nachtmann et al 2007, Kausel, Zietlow and Moore 2010). This effect corresponds to a relative increase in the power of upper harmonics of the sound spectrum when vibrations are greatest, and relative increase in the power of the lower harmonics, in particular the fundamental, when vibrations are at their least. The result is a timbral difference where a greater relative power in the upper harmonics results in a 'brighter' sound, and where the opposite results in a 'darker' sound. Studies have also found that the degree of the wall vibration is increased when the resonant frequencies of the air-column and those of the instruments' structure align. It is this principle that this work is based on. The primary objective of this work was to devise a suitable approach for incorporating the wall vibration effect into an optimisation method to investigate the optimum designs for two scenarios: maximum wall vibration and minimum wall vibration. It was also of interest to investigate if there were any design characteristics for each scenario. Two analysis methods were investigated for their suitability, namely free and forced vibration using finite element analysis (FEA). Different approaches to defining the design variables were explored and the suitability of different optimisation algorithms was investigated. The free vibration approach was found to be inadequate for this application due to the inherent omission of valuable magnitude information. The forced vibration approach was found to be more successful, although it was not possible to align a resonance with each frequency of interest

Visualisation of the Lip Motion of Brass Instrument Players, and Investigations of an Artificial Mouth as a Tool for Comparative Studies of Instruments

When playing a brass instrument the lips of the player fulfil a similar role to the cane reeds of wood-wind instruments. The nature of the motion of this lip-reed determines the ow of air through the lips, between the player's mouth and the instrument. It is a complicated feedback system in which the motion of the lips controls the air ow, which itself affects the behaviour of the lips. In recent years several designs of artificial mouth have been developed; these model the human lips using latex rubber tubes filled with water. These artificial mouths are increasingly used in experiments rather than enlisting the services of a musician as they have many advantages including greater accessibility and the stability of the embouchure. In this thesis factors affecting the reproducibility of the embouchure of one such artificial mouth are investigated with reference to the measured resonances of the lips. Using these results, procedures and practical design improvements are suggested. Two examples of comparative studies of historic instruments are presented. In order to provide detailed information on the behaviour of the lips of brass players high speed digital photography is used to image the self-oscillating lipreed. Variation in the lip opening, over a wide range of notes and different players, is investigated, providing experimental evidence to aid the process of reining physical models of the behaviour of the brass player's lips. Particular attention is paid to the relationship between the area and height of the lip opening. Results suggest that during extremely loud playing the lip motion is qualitatively similar to that in quieter notes and therefore is not the origin of the dramatic increase in the levels of the high harmonics of the radiated sound. Investigation of the behaviour at the start of a note has shown evidence relating the lip motion to the transient in the mouthpiece pressure waveform. Comparison is made between the behaviour of the artificial lips and that of the lips of musicians providing evidence of the suitability of the use of the artificial mouth as a model for real brass players. Results show that although differences exist, particularly when looking at behaviour over a wide range of dynamic levels, the general features of behaviour are reproduced by the artificial mouth

A study of brass instrument acoustics using an artificial lip reed mechanism, laser Doppler anemometry and other techniques

The self-sustained oscillation of a brass wind musical instrument involves a complex aerodynamic coupling between a multimode mechanical vibratory system (the lips of the player) and a multimode acoustical vibratory system (the air column of the instrument). In this thesis the behaviour of the coupled system near the threshold of oscillation is investigated using a simplified model in which a single mechanical lip mode is coupled to a single mode of the acoustical resonator by air flow through the lips. The theoretical threshold behaviour is compared with the measured threshold behaviour of a trombone sounded by an artificial lip reed mechanism. Comparability between theory and experiment is ensured by using model parameter values derived from mechanical response measurements on the artificial lips and input impedance measurements on the trombone.The mechanical response measurements can be used to classify mechanical modes of the artificial lips unambiguously as either "inward striking" or "outward striking". Each of the embouchures considered is found to have at least one mechanical mode of each category. The experimentally observed threshold frequencies of the coupled system suggest a behaviour which passes smoothly from "inward striking" to "outward striking" character as the trombone slide is extended or the embouchure parameters changed. It seems unlikely that this type of behaviour can be explained using a lip model with only a single degree of freedom.After a discussion of the theory of laser Doppler anemome!ry (LDA), the technique is applied to the problem of measuring the instantaneous acoustic particle velocity within a standing wave pipe driven by a loudspeaker. The resulting Doppler signals display quasi-periodic amplitude modulation with a fundamental frequency equal to the frequency of the acoustic field. The phenomenon of amplitude modulation is investigated in some detail.Two different methods of analysing Doppler signals are compared: the digit~l Hilbert transform and the Disa analogue frequency tracker; the analogue tracker is found to offer the greater signal-to-noise ratio and dynamic range. Experiments are carried out to establish how phase errors introduced by the analogue tracker can be minimised:,Velocity measurements extracted from Doppler signals using the analogue tracker are compared with the velocity deduced by applying basic theory to probe microphone pressure measurements. It is found that the acoustic particle velocity amplitude can be measured accurately over the entire frequency range considered, and the phase of the acoustic particle velocity also agrees well with theory, but not at low frequencies. LDA is successfully applied to the measurement of multi-harmonic sound fields. The technique of ensemble averaging velocity signals is shown to be particularly useful.LDA is used to measure the velocity in the backbore of a specially designed transparent mouthpiece, driven by the artificial lip reed. Although significant levels of turbulence are encountered, it is shown that acoustic components can still be clearly distinguished in frequency domain representations of the measured velocity. However LDA measurements in the mouthpiece are restricted to conditions where the acoustic particle velocity amplitude and the turbulent intensity are sufficiently low to ensure that the bandwidth of the Doppler signal is less than the bandwidth of the apparatus used to capture or process the Doppler signal.LDA measurements in brass instrument mouthpieces should provide a better understanding of the air flow into the mouthpiece and may lead to an improved model for self-sustained oscillation of the coupled system which more accurately describes the air flow

Instrument Construction: An Examination of the Effect of Lead Pipe Design Variability on Tuba Response

The document begins with a brief description of the main parts of the tuba: the mouthpiece, the valves, the body and the bell; in addition to a short explanation of the different types of material used to construct brass instruments. This study will function as the first installment of a bigger series exploring the variations in tuba sound when the different main parts are physically altered or swapped for other designs of the same part. This first installment of the series seeks to examine the section of the tuba known as the lead pipe in relation to the implications of varying the lead pipe and observing the effects of these changes. One of the goals of this research is to, through review of related literature, understand the acoustic processes that go into the creation of sound energy within a brass wind instrument. Another purpose of this writing is to discuss, through interviews of experts in the field, the lead pipe and how it is constructed, shaped, and designed, while gaining information as to how it could relate to the sound and response of the tuba. Finally, the primary objective of this study is to gather data through a series of performance tests in which the lead pipe design will be modified with results recorded

Timbral Learning for Musical Robots

abstract: The tradition of building musical robots and automata is thousands of years old. Despite this rich history, even today musical robots do not play with as much nuance and subtlety as human musicians. In particular, most instruments allow the player to manipulate timbre while playing; if a violinist is told to sustain an E, they will select which string to play it on, how much bow pressure and velocity to use, whether to use the entire bow or only the portion near the tip or the frog, how close to the bridge or fingerboard to contact the string, whether or not to use a mute, and so forth. Each one of these choices affects the resulting timbre, and navigating this timbre space is part of the art of playing the instrument. Nonetheless, this type of timbral nuance has been largely ignored in the design of musical robots. Therefore, this dissertation introduces a suite of techniques that deal with timbral nuance in musical robots. Chapter 1 provides the motivating ideas and introduces Kiki, a robot designed by the author to explore timbral nuance. Chapter 2 provides a long history of musical robots, establishing the under-researched nature of timbral nuance. Chapter 3 is a comprehensive treatment of dynamic timbre production in percussion robots and, using Kiki as a case-study, provides a variety of techniques for designing striking mechanisms that produce a range of timbres similar to those produced by human players. Chapter 4 introduces a machine-learning algorithm for recognizing timbres, so that a robot can transcribe timbres played by a human during live performance. Chapter 5 introduces a technique that allows a robot to learn how to produce isolated instances of particular timbres by listening to a human play an examples of those timbres. The 6th and final chapter introduces a method that allows a robot to learn the musical context of different timbres; this is done in realtime during interactive improvisation between a human and robot, wherein the robot builds a statistical model of which timbres the human plays in which contexts, and uses this to inform its own playing.Dissertation/ThesisDoctoral Dissertation Media Arts and Sciences 201

Experimental investigations of lip motion in brass instrument playing

The precise nature of the motion of the lips of the musician is critically important to the sound of the brass wind instrument. The player must match the oscillation of the lips to the acoustical properties of the instrument and it can take many years of practice to master the techniques involved. Visualisation techniques for capturing the motion of the lips during performance are described and the behaviour of the lips quantitatively analysed using digital image analysis. The concept of an artificial mouth for the sounding of brass wind instruments is discussed and the motion of the artificial lips is compared to that of human musicians. When a brass instrument is played loudly the energy of the higher harmonics increases, creating a distinctive ‘brassy’ timbre. It has been suggested that saturation or constraint of the lips of the musician during extremely loud playing is responsible for this change in sound. Measurements of the motion of the lips of a number of different musicians on different instruments suggest that the lips are not significantly constrained at any playing dynamic, and that it is the phenomena of nonlinear propagation and shockwave generation that is responsible for the increase in energy of the higher harmonics. It is widely accepted that the starting transient of a musical instrument is of great importance to both listener and musician. Previous studies of brass instruments have focused on the steady-state behaviour of the lip-instrument interaction. Measurements of the motion of the lips have been synchronised with the pressure in the mouthpiece of the instrument and the sound radiated from the bell in order to investigate the transient behaviour of the system during both the starting transient and slurs between notes. Thiswork has been extended to include measurements of the pressure in the mouth of the player during the starting transient, and this information used to recreate realistic transients using an artificial mouth. The transient behaviour of the system is clearly affected by the time delay between the start of the note and the acoustical feedback from the instrument beginning. The information obtained can be used to aid in the creation of accurate computational and physical models of brass wind instruments

Acoustical study of the playing characteristics of brass wind instruments

When assessing the quality of a brass instrument the player must consider a number of factors, the main consideration being the playability of the chosen instrument. The playability of an instrument is a broad term used to describe how well the instrument plays; this includes how in tune the resonant modes are, how easy it is to start and move between notes, how easy it is to bend notes and the degree of spectral enrichment during a crescendo that is able to be produced. The starting transient is known to be of crucial importance for both the musician and listener, and previous work in the field has been mainly concerned with such starting transients; this work focusses on inter-note transitions. Transitions between notes include both starting and finishing transients as the initial note is ended and the next begun. Using high speed photography images synchronised with pressure signals from the mouthpiece and bell end, the internote transitions are explored. Results from these experiments are compared with those from a simple one dimensional time domain model. Other techniques used to determine the playability of a specific instrument include the rate at which the instrument timbre becomes `brassy' due to nonlinear effects, that are a consequence of loud playing. The relative significance of viscothermal wall losses and nonlinear effects within realistic brass instruments have been explored here using experiments on cylindrical tubes of different internal diameters. These experimental results are compared with results from a computational model that uses weakly nonlinear wave propagation theory and includes viscothermal losses. It is also possible on some brass instruments, when playing loudly, to achieve what are known as super high notes; these notes are above the frequency where the instrument has well defined resonances. Experimental results are presented here using optical techniques to visualise the motion of the player's lips during playing of these super high notes