Florian Pfeifle

Measurement and physical modelling of sound hole radiations of lutes

A structural feature that can be found in many string instruments is a hollow body with one or several sound holes. The sound radiated from these holes interacts with the sound radiation from the rest of the body and perceivably influences the timbre and the loudness of the instrument. In this work three non-European lutes with sound holes are measured: the Mauretanian ginbri, the West-African gunubri, and the Chinese ruan. All of these instruments have distinct cavity air modes and a measureable Helmholtz frequency. Each instrument is measured with a 11 × 11 microphone array and analyzed with a focus on the radiated spectrum and sound intensity of the hole(s). In a further step, the findings of the measurements are compared to a Finite Element model and incorporated into a real-time finite differences physical model of the ruan.

Nonlinearities and self-organization in the sound production of the Rhodes piano

Over the last five decades the Rhodes piano became a common keyboard instrument. It is played in such diverse musical genres as Jazz, Funk, Fusion, or Pop. The sound processing of the Rhodes has not been studied in detail beforeIts sound is produced by a mechanical driven tuning fork like system causing a change in the magnetic flux of an electromagnetic pick up system. The mechanical part of the tone production consists of a small diameter tine made of stiff spring steel, the tine, and a tone bar made of brass, which is strongly coupled to the former and acts as a resonator. The system is an example for strong generator-resonator coupling. The tine acts as a generator forcing the tonebar to vibrate with its fundamental frequency. Despite of extremely different and much lower eigenfrequencies the tonebar is enslaved by the tine. The tine is of lower spatial dimension and less damped and acts nearly linear. The geometry of the tonebar is much more complex and therefore of higher dimension and damped strong...

Multisymplectic Pseudo-Spectral Finite Difference Methods for Physical Models of Musical Instruments

Physical Modeling (PM) of musical instruments has gained rising interest over the last decade. This is mainly due to the rising processing capabilities of standard computers making it possible to calculate PM solutions of complete instrument geometries in reasonable computational time or real-time using specialised hardware. Several theoretical advances of discrete solution methods developed over the last 100 years are being explored for PM of musical instruments for the first time. In this work some basic properties of two methods for PM of musical instruments a) Pseudo-Spectral Methods and b) geometry preserving methods known as symplectic (for ODEs) or multisymplectic (for PDEs) are presented and implemented. Two simplified models of musical instruments are presented as a proof of concept.

Measurement and analysis of sound radiation patterns of the chinese Ruan and the Yueqin

The chinese Yueqin and Ruan are among the oldest documented asian string instruments. Both have a long tradition in chinese music and are commonly played in orchestral music, smaller ensembles as well as solo instruments. Eventhough both instruments have similar geometrical features, like a cylindric resonance body made out of wood, they differ in several design aspects like the fixation of the strings or the presence of sound holes. In this work the effect of these differences on the radiated and percieved sound is researched. Both instruments are measured using a 11x11 microphone array. The resulting density plots of the sound radiation over the audible spectrum are compared and analyzed.

Nonlinear coupling and tension effects in a real-time physical model of a banjo

A real-time physical model of the Banjo as proposed by Pfeifle and Bader [J. Acoust. Soci. Am. (2009)] is extended with nonlinear effects on the membrane resulting from the added force of the bridge and the thereby arising anisotropic tension distribution on the membrane. It is shown that this effect directly influences the vibrational behavior of the physical model and yields a more realistic sound. In a second step a non-linear excitation mechanism of the string is presented, modeling the interaction between a standard metal banjo fingerpick and the string of the banjo. The pressure and velocity of the fingerpick are used as control parameters for the model. The whole model is implemented on a FPGA and can be played and controlled in real-time.

Membrane modes and air resonances of the banjo using physical modeling and microphone array measurements.

A fullscale physical model of a banjo is implemented using a finite‐difference formulation. The model consists of strings, bridge, resonance membrane, and the air enclosed in the geometry. The resulting time series of plucked strings in the model radiated from the membrane is integrated with respect to a room position in front of the banjo membrane and analyzed. Furthermore, the modes of the membrane are displayed as two‐dimensional mode shapes for the plucked string as well as for the free vibrating membrane. For verification and refinements of the model, measurements on a banjo were performed using a 11×11 microphone array. The recorded time series were back‐propagated to the surface of the membrane showing its vibrational patterns. These measured modes are compared to the modeed mode shapes in the low‐ to mid‐frequency range. Furthermore, the air modes of the open sound holes are investigated with respect to the their phase relations to the membrane. Radiation strength of these frequencies are strongly...

Realtime virtual banjo model and measurements using a microphone array.

A model of a full‐scale banjo was programmed in MATLAB and C using the finite differences method. Because of the highly complex algorithm, the model could not be put into practice in real time. A similar model was then written in VHDL, a hardware description language and implemented on a FPGA board. This hardware allows highly parallelized computation at highest clock rates, thereby, a realistic banjo model could be computed in real time. This virtual banjo could now be used to alter instrument‐specific parameters in real‐time. A large set of tests was conducted ranging from simple calibration of the most realistic parameters to the research of nonlinear effects on the membrane of the banjo. The findings where compared to the measurements of a real banjo done with a microphone array consisting of 128 microphones.

Impact of internal damping on forced vibrations of piano soundboards

A Finite-Difference Model of a grand piano soundboard including internal damping is used to estimate the influence of the damping on the vibration of the soundboard. Theoretically, the increase of damping reduces eigenmodes and leads to forced oscillation patterns. Those patterns show considerable dependency of their vibrational shapes upon the driving point. In the extreme case of a heavy damping, the wave starting at the driving point does not reach the boundaries of the soundboard with much strength and is therefore not reflected. Then no eigenmodes exist anymore and the plate behaves like an infinite plate. In the other extreme of a soundboard not damped at all the eigenmodes of the soundboard clearly appear. The measured patterned of a soundboard are compared to the modeled ones and conclusions are derived in terms of the amount of damping in a real soundboard.

Tone Production of the Wurlitzer and Rhodes E-Pianos

Two idiomatic examples of electro-acoustical keyboards played since the 60s to the present day are the Wurlitzer E-Piano and the Rhodes E-Piano. They are used in such diverse musical genres as Jazz, Funk, Fusion or Pop as well as in modern Electronic and Dance music. Their unique sound, that is comparable on a generic level, shows distinctive varieties in timbre and decay characteristics. This can be attributed to their specific mechanical-electromagnetic/electrostatic tone production. In this treatise, a description and comparison of the tone production mechanisms are presented based on measurements taken on both instruments, a Rhodes Mark II and a Wurlitzer EP300. The measurements include high-speed camera measurement and tracking of the primary mechanical sound production mechanisms as well as audio recordings of the unamplified instrument signal. It is highlighted that the different timbre can be attributed to different characteristics of the pickup systems of both instruments. In the case of the Rhodes, characteristic sound properties emerge due to the interaction of the mechanical motion of a small tine interacting with the magnetic field (H-field) of the pickup. In the case of the Wurlitzer a vibrating steel reed acts as the zero potential electrode of a capacitor inducing an alternating current due to changes in the electro-static field (E-field). The measurements are compared to a FEM model of the respective geometry showing good accordance with the proposed effects. A simplified physical model is proposed for both instruments along with a more complete physical model taking the geometry of the sound production mechanisms of the instruments into account.

No latency feedback controller coupled to real-time physical models using programmable hardware

Over the last years, advances in technology and methodology made it possible to simulate and synthesize highly realistic finite difference (FD) models in real-time or close to real-time. Still, most conventional processing platforms introduce latency to the signal processing chain due to sequential processing and/or communication protocol timing and throughput restrictions. This can act as a severe penalty when developing expressive controller interfaces for large geometry physical models. Using field programmable gate array (FPGA) hardware enables highly customized interface and FD model designs that are able to meet hard real-time requirements even for large physical models. In this work, a modified five-string banjo coupled to a real-time physical modeling synthesis application running on an FPGA development board is presented. The proposed methodology is an extension of an existing PCIe enabled interface which was primarily developed for research applications. The new interface is aimed at facilitatin...