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

Use of the Montreal Cognitive Assessment as an Early Indicator of Tumor Progression in Patient with Stage III and IV Gliomas

Patients diagnosed with high grade glioma have a short life expectancy due to rapid progression of disease following and/or during treatment. Magnetic resonance imaging (MRI) is the primary method of surveying tumor progression, but is costly, lengthy in duration and often uncomfortable for the patient. An alternative to MRI that is cost efficient and patient friendly is of great interest to the medical community. If this alternative could also provide advanced notification of disease progression, then this patient population would have the opportunity for earlier treatment and the potential for greater efficacy. To pursue this concept, we assessed whether the Montreal Cognitive Assessment (MoCA) could be that MRI alternative, potentially providing an early identifier of disease progression for the high grade glioma population. We retrospectively assessed a variety of medical and surgical data points, in conjunction with the MoCA scores for individuals with a high grade glioma diagnosis who received surgery and/or biopsy with radiation treatment and had at least one instance of disease progression. Of the 128 subjects intended to fulfill our sample size requirement, only 5 subjects qualified for enrollment. Our statistical tests were greatly impacted by this unfortunate circumstance and because of this we were not able to support the MoCA as hypothesized because the results did not reach the level of statistical significance. We have identified many interesting trends, but without an appropriate sample size these cannot be validated. We hope the study concept and design will provide the basis for future research that can build upon our hypothesis and provide a definite answer

Spectral pitch distance and microtonal melodies

We present an experiment designed to test the effectiveness of spectral pitch distance at modeling the degree of “affinity” or “fit” of pairs of successively played tones or chords (spectral pitch distance is the cosine distance between salience-weighted, Gaussian-smoothed, pitch domain embeddings of spectral pitches—typically the first eight to ten partials of a tone). The results of a previously conducted experiment, which collected ratings of the perceived similarity and fit of root-position major and minor triads, suggest the model works well for pairs of triads in standard 12-tone equal temperament tunings. The new experiment has been designed to test the effectiveness of spectral pitch distance at modeling the affinity of tones in microtonal melodies where the partials of the tones can be variably tempered between being perfectly harmonic and perfectly matched to the underlying microtonal tuning. The use of microtonal tunings helps to disambiguate innate perceptual (psychoacoustical) responses from learned (cultural) responses. Participants are presented with a software synthesizer containing two unlabeled controls: one adjusts the precise tuning of the tones; the other adjusts the extent to which the spectrum is tempered to match the tuning (as set by the first control). A selection of microtonal melodies are played in different tunings, and the participants adjust one, or both, controls until they find a “sweet spot” at which the music sounds most “in-tune” and the notes best “fit” together. The results of these experiments will be presented and discussed

Materials in Centrifugal Compressor and Steam Turbines: Selection, Processing, and Repair

Short CoursesMaterials selection is significant with respect to performance, reliability, and longevity of turbomachinery, particularly given the increasing severity of the process environments. The trends are that the selection is becoming a cooperative effort between the OEM’s and the customers and it is vital that all parties understand the implications of the materials selection and necessary manufacturing processes. This course reviews the material selection for major components for centrifugal compressors and steam turbines coving topics such as materials of construction, heat treatments, properties, fabrication and manufacturing methods, inspection methods, and compliance with industry specifications such as API and NACE along with other special requirements. Going beyond new equipment, the course will touch on the identification of damage mechanisms through root cause analysis and then delve into the procedures and documentation required to restore the components to operating condition. The course will end with a discussion of various coatings and surface treatments that can also be used to enhance the performance and/or longevity of the equipment

Metrics for pitch collections

Models of the perceived distance between pairs of pitch collections are a core component of broader models of the perception of tonality as a whole. Numerous different distance measures have been proposed, including voice-leading, psychoacoustic, and pitch and interval class distances; but, so far, there has been no attempt to bind these different measures into a single mathematical framework, nor to incorporate the uncertain or probabilistic nature of pitch perception (whereby tones with similar frequencies may, or may not, be heard as having the same pitch). To achieve these aims, we embed pitch collections in novel multi-way expectation arrays, and show how metrics between such arrays can model the perceived dissimilarity of the pitch collections they embed. By modeling the uncertainties of human pitch perception, expectation arrays indicate the expected number of tones, ordered pairs of tones, ordered triples of tones and so forth, that are heard as having any given pitch, dyad of pitches, triad of pitches, and so forth. The pitches can be either absolute or relative (in which case the arrays are invariant with respect to transposition). We provide a number of examples that show how the metrics accord well with musical intuition, and suggest some ways in which this work may be developed

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

A spectral pitch class model of the probe tone data and scalic tonality

In this paper, we introduce a small family of novel bottom-up (sensory) models of the Krumhansl and Kessler (1982) probe tone data. The models are based on the spectral pitch class similarities between all twelve pitch classes and the tonic degree and tonic triad. Cross-validation tests of a wide selection of models show ours to have amongst the highest fits to the data. We then extend one of our models to predict the tonics of a variety of different scales such as the harmonic minor, melodic minor, and harmonic major. The model produces sensible predictions for these scales. Furthermore, we also predict the tonics of a small selection of microtonal scales—scales that do not form part of any musical culture. These latter predictions may be tested when suitable empirical data have been collected

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

METS2 Short Course 8

Short Cours

Hex Player—a virtual musical controller

In this paper, we describe a playable musical interface for tablets and multi-touch tables. The interface is a generalized keyboard, inspired by the Thummer, and consists of an array of virtual buttons. On a generalized keyboard, any given interval always has the same shape (and therefore fingering); furthermore, the fingering is consistent over a broad range of tunings. Compared to a physical generalized keyboard, a virtual version has some advantages—notably, that the spatial location of the buttons can be transformed by shears and rotations, and their colouring can be changed to reflect their musical function in different scales. We exploit these flexibilities to facilitate the playing not just of conventional Western scales but also a wide variety of microtonal generalized diatonic scales known as moment of symmetry, or well-formed, scales. A user can choose such a scale, and the buttons are automatically arranged so their spatial height corresponds to their pitch, and buttons an octave apart are always vertically above each other. Furthermore, the most numerous scale steps run along rows, while buttons within the scale are light-coloured, and those outside are dark or removed. These features can aid beginners; for example, the chosen scale might be the diatonic, in which case the piano’s familiar white and black colouring of the seven diatonic and five chromatic notes is used, but only one scale fingering need ever be learned (unlike a piano where every key needs a different fingering). Alternatively, it can assist advanced composers and musicians seeking to explore the universe of unfamiliar microtonal scales