Development and Evaluation of a Hybrid Wind Instrument

A hybrid wind instrument generates self-sustained sounds via a real-time interaction between a computed excitation model (such as the physical model of human lips interacting with a mouthpiece) and a real acoustic resonator. Attempts to produce a hybrid instrument have so far fallen short, in terms of both the accuracy and the variation in the sound produced. The principal reason for the failings of previous hybrid instruments is the actuator which, controlled by the excitation model, introduces a fluctuating component into the air flow injected into the resonator. In the present thesis, the possibility of using a loudspeaker to supply the calculated excitation signal is evaluated; the loudspeaker is placed at the entrance of the resonator (a clarinet-like tube), along with a microphone. This work focusses particularly on two possibilities: using the instrument as a new musical instrument and using it as a tool to carry out wind instrument research. First, a theoretical study facilitates the modelling of the loudspeaker-resonator system and the design of a feedback and feedforward filter to successfully compensate for the presence of the loudspeaker. The prototype is then evaluated using physical models of a single-reed, a lip-reed and a bow-string interaction and using a purely mathematical “polynomial” excitation model. For the design of excitation models, the usefulness of dimensionless and reduced parameter forms is outlined, and a sound prediction theory is presented, enabling the pre-estimation of both amplitude and spectral related features of the self-sustained sounds. The resulting self-sustained sounds are evaluated by a mapping of their sound descriptors to the input parameters of the excitation models, both for sustained and attack sounds. For all excitation models, the sounds produced by the hybrid instrument are shown to match those predicted by simulation. However, the hybrid instrument is more easily destabilised for certain extreme parameter states

Developing and evaluating a hybrid wind instrument

A hybrid wind instrument generates self-sustained sounds via a real-time interaction between a computed excitation model (such as the physical model of human lips interacting with a mouthpiece) and a real acoustic resonator. Attempts to produce a hybrid instrument have so far fallen short, in terms of both the accuracy and the variation in the sound produced. The principal reason for the failings of previous hybrid instruments is the actuator which, controlled by the excitation model, introduces a fluctuating component into the air flow injected into the resonator. In the present paper, the possibility of using a loudspeaker to supply the calculated excitation signal is evaluated. A theoretical study has facilitated the modeling of the loudspeaker-resonator system and the design of a feedback and feedforward filter to successfully compensate for the presence of the loudspeaker. The resulting self-sustained sounds are evaluated by a mapping of their sound descriptors to the input parameters of the physical model of the embouchure, both for sustained and attack sounds. Results are compared with simulations. The largely coherent functioning confirms the usefulness of the device in both musical and research contexts

Improving the stability of a hybrid wind instrument using two microphones

A hybrid wind instrument is constructed by putting a theoretical excitation model (such as a real-time computed physical model of a clarinet embouchure) in interaction with a real wind instrument resonator. In previous work, the successful construction of a hybrid wind instrument has been demonstrated, with the interaction facilitated by a loudspeaker and a single microphone placed at the entrance of a clarinet-like tube. The prototype was evaluated using physical models of a single-reed, a lip-reed and a bow-string interaction. Musically relevant results were obtained when the negative gradient of the nonlinear excitation function was limited to a certain threshold. When surpassed, erroneous noises appeared. In the present paper, a study of the open-loop system (the input-to-output response excluding the excitation model) reveals that this instability is caused by strong, high-frequency resonance peaks combined with an inverted phase response. The high frequency resonance peaks appear to result from non-planar air vibration modes in the small cavity in front of the loudspeaker. Hence, they are avoided by repositioning the microphone at the centre of the loudspeaker cavity. Meanwhile, the inverted phase state occurs due to various phase lag sources such as the inevitable input-to-output latency of the computing system. This is accounted for by introducing a second microphone a distance c.Δt along the tube (where c is the speed of sound and Δt the latency). The excitation models are implemented on a new digital real-time audio platform, “Bela”, supporting multiple audio inputs. A better stability is obtained and evaluation with a real clarinet gives musically relevant results

On The Accuracy Of Calculation Of The Impedance Spectra Of Woodwind Instruments

Most woodwind instruments in museums may not be played, because of the risk of damage. However, if the acoustic impedance spectra (tube resonances) can be measured or calculated, many conclusions may be drawn about, for example, pitch, timbre, intonation, utility of alternative fingerings and effects of bore shrinkage. Impedance measurement methods may sometimes be applied to instruments in museums, but are only meaningful if the instrument is in good playing condition, free from leaks. However, the overwhelming contribution to the acoustic properties of a woodwind is made by the shape of its air column. If the bore shape and tone holes are measured sufficiently accurately, we may compute the acoustic impedance of the instrument for all fingerings using standard equations of linear acoustics. This methodology has been thoroughly tested by applying it to a Heckel bass clarinet in A (German system) from 1910. This working instrument has been kept continuously in good playing condition but has seen relatively light use. Measurements were made using a calibrated tape measure and (plastic) Vernier calipers, which minimized bore damage. The results were compared with experimental measurement of acoustic impedances using a BIAS system at the Open University. Impedance calculation software was written in MatLab™ following the scheme of Plitnik and Strong , using the later developments by Keefe , Cronin and Dalmont et al. For all fingerings the impedance peaks agreed with the calculations, on average to better than 10 cents in frequency for the peak forming the basis of the sounding note. This could be empirically corrected by an end correction of 3 mm (on a 1350 mm instrument). The reed/embouchure impedance was semi-empirically corrected by an end correction of 17 mm, which is consistent with the theory and experiments of Dalmont et al.4 on soprano clarinets. Playing tests were in good agreement. The playing frequencies agreed well with the calculations using the above end corrections, both when the mouthpiece was fully pushed in and when it was pulled out by 10.8 mm to correct overall intonation. The calculations also correctly predicted the excellent tuning and timbre of the fork fingering for written Bb2, the “patent C#” fingering for C#3 and the unsuitability of the fork fingering for Eb2, which was about a quarter-tone sharp. The ‘impedance mapping’ method of Jeltsch et al. has been further developed into a powerful tool for summarizing the acoustical behavior of a complete instrument and comparing it with other instruments. A new method of determining the cut-off phenomenon in woodwind instruments, utilizing the higher resonances in the tube, has shown that there is a cut-off band rather than a single frequency. In the case of the Heckel, the Benade approximation gives a cut-off frequency of 1000 Hz, whereas there is actually a range of 920 - 1320 Hz, dependent on the fingering. These methods are being applied to the study of non-playable bass clarinets in museum collections, in an attempt to elucidate musical differences between instruments of different designs

A comparison of single-reed and bowed-string excitations of a hybrid wind instrument

A hybrid wind instrument is constructed by connecting a theoretical excitation model (such as a real-time computed physical model of a single-reed mouthpiece) to a loudspeaker and a microphone which are placed at the entrance of a wind instrument resonator (a clarinet-like tube in our case). The successful construction of a hybrid wind instrument, and the evaluation with a single-reed physical model, has been demonstrated in previous work. In the present paper, inspired by the analogy between the principal oscillation mechanisms of wind instruments and bowed string instruments, we introduce the stick-slip mechanism of a bow-string interaction model (the hyperbolic model with absorbed torsional waves) to the hybrid wind instrument set-up. Firstly, a dimensionless and reduced parameter form of this model is proposed, which reveals the (dis-)similarities with the single-reed model. Just as with the single-reed model, the hybrid sounds generated with the bow-string interaction model are close to the sounds predicted by a complete simulation of the instrument. However, the hybrid instrument is more easily destabilised for high bowing forces. The bow-string interaction model leads to the production of some raucous sounds (characteristic to bowed-string instruments, for low bowing speeds) which represents the main perceived timbral difference between it and the single-reed model. Another apparent timbral difference is the odd/even harmonics ratio, which spans a larger range for the single-reed model. Nevertheless, for both models most sound descriptors are found within the same range for a (stable) variety of input parameters so that the differences in timbre remain relatively low. This is supported by the similarity of both excitation models and by empirical tests with other, more dynamic excitation models

Developing and evaluating a hybrid wind instrument excited by a loudspeaker

A hybrid wind instrument generates self-sustained sounds via a real-time interaction between a computed physical model of an embouchure and a real acoustic resonator. This concept remains poorly investigated due to the technical demands on the actuator that supplies the calculated mouthpiece signal. A newly proposed prototype has been realized, using a loudspeaker as actuator. We evaluate the resulting self-sustained sounds by mapping their sound descriptors to the input parameters of the physical model of the embouchure. Results are compared with simulations. The largely coherent functioning confirms the usefulness of the device in both musical and research contexts

Sustained and attack sounds of the hybrid instrument evaluation, along with simulations. Mouthpiece pressure and external pressures.

These sounds are produced by the hybrid wind instrument with a single-reed excitation and by an entirely simulated wind instrument. The mouthpiece parameters are varied so as to evaluate both attack and sustained sounds over the stable operation range of the hybrid instrument. These results are discussed in depth in a paper on the development and evaluation of the hybrid wind instrument (to appear)

Development of a hybrid wind instrument—Some key findings

A hybrid wind instrument is constructed by putting a theoretical excitation model (such as a real-time computed physical model of a clarinet embouchure) in interaction with a real wind instrument resonator. In previous work, the successful construction of a hybrid wind instrument has been demonstrated, with the interaction facilitated by a loudspeaker and a microphone placed at the entrance of a clarinet-like tube. The present paper focuses on some key findings, concentrating particularly on the “musical instrument” and “research tool” perspectives. The limitations of the hybrid set-up are considered. In particular, the choice of the loudspeaker used in the set-up is explained and the occurrence (and prevention) of instabilities during the operation of the hybrid instrument are discussed. For the design of excitation models used to drive the hybrid instrument, the usefulness of dimensionless and reduced parameter forms is outlined. In contrast to previously reported physically based excitation models, it is demonstrated that a purely mathematical “polynomial model” enables an independent control of separate sound features. For all excitation models, the sounds produced with the hybrid instrument are shown to match to those predicted by simulation. However, the hybrid instrument is more easily destabilized for certain extreme parameter states

C++ code for the hybrid instrument evaluation on the Bela platform

The C++ code, designed for execution on the real-time audio  platform "Bela" (http://bela.io/), to operate the hybrid wind instrument (using 2 microphones).<br

A hybrid reed instrument: an acoustical resonator with a numerically simulated mouthpiece

International audienceA study on the development of a hybrid wind instrument is carried out. An acoustical tube interacts with a numerically simulated mouthpiece in real-time, with the aim to propose in the long term both a tool for objective measurements, and a new musical instrument, easily playable, with unique timbral capacities. This preliminary study focusses on a first prototype, to verify the physical meaningfulness and estimate its potential. A microphone at the tube entrance feeds a numerical model of the reed used to compute the volume flow through the reed channel. This is the output of the numerical part, which is directed to an electrovalve that proportionally modulates the volume flow between the compressed air source and the tube entrance. The hybrid instrument is characterized by studying its parts separately (evaluation of the electrovalve characteristics, impedance measurement of the resonator), but also as a whole by analyzing its behaviour when the parameters of the mouthpiece are varied. Both transients and steady regimes are compared to a fully simulated instrument. We observed a coherent functioning for fundamental frequencies sufficiently below the electrovalves first resonant frequency. The foremost drawbacks are associated to the electrovalves mechanics and to noisy pressure measurements