Download Drumkit Transcription via Convolutive NMF
Audio to midi software exists for transcribing the output of a multimic’ed drumkit. Such software requires that the drummer uses multiple microphones to capture a single stream of audio for each kit piece. This paper explores the first steps towards a system for transcribing a drum score based upon the input of a single mono microphone. Non-negative Matrix Factorisation is a widely researched source separation technique. We describe a system for transcribing drums using this technique presenting an improved gains update method. A good level of accuracy is achieved on on complex loops and there are indications the mis-transcriptions are for perceptually less important parts of the score.
Download Real-time Finite Difference Physical Models of Musical Instruments on a Field Programmable Gate Array (FPGA)
Real-time sound synthesis of musical instruments based on solving differential equations is of great interest in Musical Acoustics especially in terms of linking geometry features of musical instruments to sound features. A major restriction of accurate physical models is the computational effort. One could state that the calculation cost is directly linked to the geometrical and material accuracy of a physical model and so to the validity of the results. This work presents a methodology for implementing realtime models of whole instrument geometries modelled with the Finite Differences Method (FDM) on a Field Programmable Gate Array (FPGA), a device capable of massively parallel computations. Examples of three real-time musical instrument implementations are given, a Banjo, a Violin and a Chinese Ruan.
Download Soliton Sonification - Experiments with the Kortweg-deVries Equation
Solitons are special solutions of certain nonlinear partial differential equations of mathematical physics. They exhibit properties that are partly similar to the solutions of the linear wave equation and partly similar to the behaviour of colliding particles. Their characteristic features are well-known in the mathematical literature but few closed-form solutions are available. This contribution derives algorithmic structures for the computation of solitons in a dimensionless space-time domain which can be scaled to the audio frequency range. The investigations are confined to first and second order solutions of the Korteweg-de Vries equation. Sound examples show that the effects of wave propagation and soliton interaction can be represented by audible events.
Download A pickup model for the Clavinet
In this paper recent findings on magnetic transducers are applied to the analysis and modeling of Clavinet pickups. The Clavinet is a stringed instrument having similarities to the electric guitar, it has magnetic single coil pickups used to transduce the string vibration to an electrical quantity. Data gathered during physical inspection and electrical measurements are used to build a complete model which accounts for nonlinearities in the magnetic flux. The model is inserted in a Digital Waveguide (DWG) model for the Clavinet string for its evaluation.
Download A Physically-Constrained Source Model for FDTD Acoustic Simulation
The Finite Difference Time Domain (FDTD) method is becoming increasingly popular for room acoustics simulation. Yet, the literature on grid excitation methods is relatively sparse, and source functions are traditionally implemented in a hard or additive form using arbitrarily-shaped functions which do not necessarily obey the physical laws of sound generation. In this paper we formulate a source function based on a small pulsating sphere model. A physically plausible method to inject a source signal into the grid is derived from first principles, resulting in a source with a nearflat spectrum that does not scatter incoming waves. In the final discrete-time formulation, the source signal is the result of passing a Gaussian pulse through a digital filter simulating the dynamics of the pulsating sphere, hence facilitating a physically correct means to design source functions that generate a prescribed sound field.
Download Analysis of Sound Field Distribution for Room Acoustics: From the Point of View of Hardware Implementation
Analysis of sound field distribution is a data-intense and memory-intense application. To speed up calculation, an alternative solution is to implement the analysis algorithms by FPGA. This paper presents the related issues for FPGA based sound field analysis system from the point of view of hardware implementation. Compared with other algorithms, the OCTA-FDTD algorithm consumes 49 slices in FPGA, and the system updates 536.2 million elements per second. In system architecture, the system based on the parallel architecture benefits from fast computation since the sound pressures of all elements are obtained and updated at a clock cycle. But it consumes more hardware resources, and a small sound space is simulated by a FPGA chip. In contrast, the system based on the time-sharing architecture extends the simulated sound area by expense of computation speed since the sound pressures are calculated element by element.
Download Binaural simulations using audio rate FDTD schemes and CUDA
Three dimensional finite difference time domain schemes can be used as an approach to spatial audio simulation. By embedding a model of the human head in a 3D computational space, such simulations can emulate binaural sound localisation. This approach normally relies on using high sample rates to give finely detailed models, and is computationally intensive. This paper examines the use of head models within audio rate FDTD schemes, ranging from 176.4 down to 44.1 kHz. Using GPU computing with Nvidia’s CUDA architecture, simulations can be accelerated many times over a serial computation in C. This allows efficient, dynamic simulations to be produced where sounds can be moved around during the runtime. Sound examples have been generated by placing a personalised head model inside an anechoic cube. At the lowest sample rate, 44.1 kHz, localisation is clear in the horizontal plane but much less so in the other dimensions. At 176.4, there is far greater three dimensional depth, with perceptible front to back, and some vertical movement.
Download A Study on Dynamic Vocal Tract Shaping for Dipthong Simulation Using a 2D Digital Wavegude Mesh
This paper presents a study of an articulatory-based speech synthesis based on a 2D-Digital Waveguide Mesh (2D-DWM) to model acoustic wave propagation in the oral tract. It is employed to study the effects of changing oral tract area, and in particular, of moving the articulators during the production of diphthongs. The operation of the synthesizer including details of how diphthongs are produced are discussed. The results support earlier findings that the wall reflection coefficient is inversely proportional to the formant bandwidth.
Download Achieving Convolution-based Reverberation Through use of Geometric Acoustic Modelling Techniques
Download Pitch Shifting of Audio Signals Using the Constant-Q Transform
Pitch-scale modifications of polyphonic music are usually performed by manipulating the time-frequency representation of the input signal. Most approaches proposed in the past are thereby based on the Fourier transform although its linear frequency bin spacing is known to be inadequate to some degree for analysing and processing music signals. Recently invertible constant-Q transforms (CQT) featuring high Q-factors have been proposed exhibiting a more suitable geometrical bin spacing. In this paper a frequency domain pitch-shifting approach based on the CQT is proposed. The CQT is specifically attractive for pitch-shifting because it can be implemented by frequency translation (shifting partials along the frequency axis) as opposed to spectral stretching in the Fourier transform domain. Furthermore, the high time resolution of CQT at high frequencies improves transient preservation. Audio examples are provided to illustrate the results achieved with the proposed method.