Rolf Bader

Individual reed characteristics due to changed damping using coupled flow‐structure and time‐dependent geometry changing Finite‐Element calculation

The vibration of a reed of a saxophone is calculated using a 2D model of the mouth cavity, the mouth piece and the reed. The time‐dependent Finite‐Element calculation takes the flow‐structure interaction into account and changes the geometry of the flow according to the reed vibration in time. The model is used to study the flow behaviour, pressure distribution, reed vibration and reaction to disturbances of the system. A constant pressure is assumed at the mouth cavity to simulate the pressure of the players lungs. During the time‐dependent process, an impulse is modeled at the end of the mouth piece travelling back from the end of the tube. The damping of the reed was changed to study the reed behaviour. Hard damped reeds show a simple and stable impulse behaviour causing a clear pressure impulse. When the damping is decreased, the impulse coming back from the end of the tube causes the reed not only to open and close but also to show additional vibrations caused by the interplay of the reeds eigenfre...

Sound - Perception - Performance

Musical Performance covers many aspects like Musical Acoustics, Music Psychology, or motor and prosodic actions. It deals with basic concepts of the origin or music and its evolution, ranges over neurocognitive foundations, and covers computational, technological, or simulation solutions. This volume gives an overview about current research in the foundation of musical performance studies on all these levels. Recent concepts of synchronized systems, evolutionary concepts, basic understanding of performance as Gestalt patterns, theories of chill as performance goals or historical aspects are covered. The neurocognitive basis of motor action in terms of music, musical syntax, as well as therapeutic aspects are discussed. State-of-the-art applications in performance realizations, like virtual room acoustics, virtual musicians, new concepts of real-time physical modeling using complex performance data as input or sensor and gesture studies with soft- and hardware solutions are presented. So although the field is still much larger, this volume presents current trends in terms of understanding, implementing, and perceiving performance.

Radiation characteristics of multiple and single sound hole vihuelas and a classical guitar

Two recently built vihuelas, quasi-replicas of the Spanish Renaissance guitar, one with a small body and one sound hole and one with a large body with five sound holes, together with a classical guitar are investigated. Frequency dependent radiation strengths are measured using a 128 microphone array, back-propagating the frequency dependent sound field upon the body surface. All three instruments have a strong sound hole radiation within the low frequency range. Here the five tone holes vihuela has a much wider frequency region of strong sound hole radiation up to about 500 Hz, whereas the single hole instruments only have strong sound hole radiations up to about 300 Hz due to the enlarged radiation area of the sound holes. The strong broadband radiation of the five sound hole vihuela up to about 500 Hz is also caused by the sound hole phases, showing very consistent in-phase relations up to this frequency range. Also the radiation strength of the sound holes placed nearer to the center of the sound box are much stronger than those near the ribs, pointing to a strong position dependency of sound hole to radiation strength. The Helmholtz resonance frequency of the five sound hole vihuela is influenced by this difference in radiation strength but not by the rosettas, which only have a slight effect on the Helmholtz frequency.

Reconstruction of radiating sound fields using minimum energy method.

A method for reconstructing a pressure field at the surface of a radiating body or source is presented using recording data of a microphone array. The radiation is assumed to consist of many spherical radiators, as microphone positions are present in the array. These monopoles are weighted using a parameter alpha, which broadens or narrows the overall radiation directivity as an effective and highly intuitive parameter of the radiation characteristics. A radiation matrix is built out of these weighted monopole radiators, and for different assumed values of alpha, a linear equation solver reconstructs the pressure field at the bodys surface. It appears that from these many arbitrary reconstructions, the correct one minimizes the reconstruction energy. The method is tested, localizing the radiation points of a Balinese suling flute, reconstructing complex radiation from a duff frame drum, and determining the radiation directivity for the first seven modes of an Usbek tambourine. Stability in terms of measurement noise is demonstrated for the plain method, and additional highly effective algorithm is added for a noise level up to 0 dB. The stability of alpha in terms of minimal reconstruction energy is shown over the whole range of possible values for alpha. Additionally, the treatment of unwanted room reflections is discussed, still leading to satisfactory results in many cases.

Characterization of guitars through fractal correlation dimensions of initial transients

Abstract Three guitars are characterized using 96 initial transients each, recorded over four strings, playing with four notes on each string, apoyando and tirando and in three different loudnesses. These initial sounds have been analysed using the fractal correlation dimension algorithm, which shows the number of rules, that is the number of perceivable components, governing the sound. It is shown that the sound character of the instruments can be seen within the overall mean values and standard deviations of the different strings, attacks and volumes. The reasons for the different values are mostly inharmonic frequency components in the initial transient caused by resonant frequencies of the body. The minimum energy needed to drive these resonances could be a way for guitar-builders to determine the loudness and presence of their instruments. Also a pre-scratch-sound, the sound of a finger scratching along the string before releasing it, is shown to contain almost the whole overtone structure of the following sound and could be used to pre-determine the pitch or identify the instrument as a guitar.

Aeroacoustical coupling and synchronization of organ pipes

A synchronization experiment on two mutual interacting organ pipes is compared with a theoretical model which takes into account the coupling mechanisms by the underlying first principles of fluid mechanics and aeroacoustics. The focus is on the Arnold-tongue, a mathematical object in the parameter space of detuning and coupling strength which quantitatively captures the interaction of the synchronized sound sources. From the experiment, a nonlinearly shaped Arnold-tongue is obtained, describing the coupling of the synchronized pipe-pipe system. This is in contrast to the linear shaped Arnold-tongue found in a preliminary experiment of the coupled system pipe-loudspeaker. To understand the experimental result, a coarse-grained model of two nonlinear coupled self-sustained oscillators is developed. The model, integrated numerically, is in very good agreement with the synchronization experiment for separation distances of the pipes in the far field and in the intermediate field. The methods introduced open the door for a deeper understanding of the fundamental processes of sound generation and the coupling mechanisms on mutual interacting acoustic oscillators.

Phase synchronization in the cochlea at transition from mechanical waves to electrical spikes.

Measured auditory nervous spikes often show synchronization, phase-locking, or entrainment (P. Cariani, Neural Plast. 6(4), 142-172 (1999) and Kumaresana et al., J. Acoust. Soc. Am. 133(6), 4290-4310 (2013). Physiologically synchronization is found in the anteroventral cochlear nucleus (Joris et al., J. Neurophysiol. 71(3), 1022-1036 (1994)) or in the trapezoid body also between critical bandwidths (Louage et al., Auditory Signal Processing: Physiology, Psychoacoustics, and Models (Springer, New York, 2004), pp. 100-106). The effect is an enhancement of pitch detection, spatial localization, or speech intelligibility. To investigate the presence of synchronization already in the cochlea, in the present paper, a finite-difference time-domain model of the cochlea is implemented with conditions for spike excitation caused by mechanical basilar membrane displacement. This model shows synchronization already in the cochlea at the transition from mechanical waves to nerve spike excitation. Using a sound as model input consisting of ten harmonic overtones with random phase relations, the output spikes are strongly phase aligned after this transition. When using a two-sinusoidal complex as input, and altering the phase relations between the two sinusoidals, the output spikes show the higher sinusoidal shifting the phase of the lower one in its direction in a systematic way. Therefore, already during the transition from mechanical to electrical excitation within the cochlea, synchronization appears to be improving perception of pitch, speech, or localization.

Finite‐element calculation of a bass drum

The bass drum of a drum kit used with rock or jazz music is modeled as a 3D geometry in a transient finite‐element formulation. The geometry was taken from a Gretch drum set called ‘‘Vinnie Colaiuta’’ with no cushion damping within the drum or at the resonance membrane. The 12 cross layers or wood used for the drum body was assumed to result in an isotropical Young’s modulus all over the wood. The drum was modeled with air enclosed, with the beating and resonating membranes being coupled to the air and to the wooden rim of the drum body. Also, as a starting point of the transient calculation, the strain of the wooden body caused by the tension of the membranes was taken into consideration. The transient model started with a beating on the front membrane and the radiation of the system was integrated over the radiating area. The results are compared to recordings of a real bass drum of this Gretch drum set.

Complete geometric computer simulation of a classical guitar

The aim of formulating a complete model of a classical guitar body as a transient‐time geometry is to get detailed insight into the vibrating and coupling behavior of the time‐dependent guitar system. Here, especially the evolution of the guitars initial transient can be looked at with great detail and the produced sounds from this computer implementation can be listened to. Therefore, a stand‐alone software was developed to build, calculate, and visualize the guitar. The model splits the guitar body into top plate, back plate, ribs, neck, inclosed air, and strings and couples these parts together including the coupling of bending waves and in‐plane waves of these plates to serve for a better understanding of the coupling between the guitar parts and between these two kinds of waves. The resulting waveforms are integrated over the geometry and the resulting sounds show up the different roles and contributions of the different guitar body parts to the guitar sound. Here cooperation with guitar makers is es...

Cochlear spike synchronization and neuron coincidence detection model

Coincidence detection of a spike pattern fed from the cochlea into a single neuron is investigated using a physical Finite-Difference model of the cochlea and a physiologically motivated neuron model. Previous studies have shown experimental evidence of increased spike synchronization in the nucleus cochlearis and the trapezoid body [Joris et al., J. Neurophysiol. 71(3), 1022-1036 and 1037-1051 (1994)] and models show tone partial phase synchronization at the transition from mechanical waves on the basilar membrane into spike patterns [Ch. F. Babbs, J. Biophys. 2011, 435135]. Still the traveling speed of waves on the basilar membrane cause a frequency-dependent time delay of simultaneously incoming sound wavefronts up to 10 ms. The present model shows nearly perfect synchronization of multiple spike inputs as neuron outputs with interspike intervals (ISI) at the periodicity of the incoming sound for frequencies from about 30 to 300 Hz for two different amounts of afferent nerve fiber neuron inputs. Coincidence detection serves here as a fusion of multiple inputs into one single event enhancing pitch periodicity detection for low frequencies, impulse detection, or increased sound or speech intelligibility due to dereverberation.