Download The development of an online course in DSP eartraining The authors present a collaborative effort on establishing an online course in DSP eartraining. The paper reports from a preliminary workshop that covered a large range of topics such as eartraining in music education, terminology for sound characterization, e-learning, automated tutoring, DSP techniques, music examples and audio programming. An initial design of the web application is presented as a rich content database with flexible views to allow customized online presentations. Technical risks have already been mitigated through prototyping.
Download User-Guided Variable-Rate Time-Stretching Via Stiffness Control User control over variable-rate time-stretching typically requires direct, manual adjustment of the time-dependent stretch rate. For time-stretching with transient preservation, rhythmic warping, rhythmic emphasis modification, or other effects that require additional timing constraints, however, direct manipulation is difficult. For a more user-friendly approach, we present work that allows a user to specify a time-dependent stiffness curve to warp the time axis of a recording, while maintaining other timing constraints, such as a desired overall recording length or musical rhythm quantization (e.g. straight-to-swing), providing a notion of stretchability to sound. To do so, the user-guided stiffness curve and timing constraints are translated into the desired time-dependent stretch rate via a constrained optimization program motivated by a physical spring system. Once the time-dependent stretch rate is computed, appropriately modified variable-rate time-stretch processors are used to process the sound. Initial results are demonstrated using both a phase-vocoder and pitch-synchronous overlap-add processor.
Download Spatial High Frequency Extrapolation Method for Room Acoustic Auralization Auralization of numerically modeled impulse responses can be informative when assessing the geometric characteristics of a room. Wave-based acoustic modeling methods are suitable for approximating low frequency wave propagation. Subsequent auralizations are perceived unnaturally due to the limited bandwidth involved. The paper presents a post-processing framework for extending low-mid frequency band limited spatial room impulse responses (SRIR) to include higher frequency signal components without the use of geometric modeling methods. Acoustic parameters for extrapolated RIRs are compared with reference measurement data for existing venues and a Finite Difference Time Domain modeled SRIR is extrapolated to produce a natural sounding full-band SRIR signal. The method shows promising agreement particularly for large venues as the air absorption is more dominant than the boundary absorption at high frequencies.
Download Simulation of Fender Type Guitar Preamp using Approximation and State-Space Model This paper deals with usage of approximations for simulation of more complex audio circuits. A Fender type guitar preamp was chosen as a case study. This circuit contains two tubes and thus four nonlinear functions as well as it is a parametric circuit because of an integrated tone stack. A state-space approach was used for simulation and further, precomputed solution is approximated using nonuniform cubic splines.
Download Real-time Auralisation System for Virtual Microphone Positioning A computer application was developed to simulate the process of microphone positioning in sound recording applications. A dense, regular grid of impulse responses pre-recorded on the region of the room under study allowed the sound captured by a virtual microphone to be auralised through real-time convolution with an anechoic stream representing the sound source. Convolution was performed using a block-based variation on the overlap-add method where the summation of many small subconvolutions produced each block of output data samples. As the applied RIR filter varied on successive audio output blocks, a short cross fade was applied to avoid glitches in the audio. The maximum possible length of impulse response applied was governed by the size of audio processing block (hence latency) employed by the program. Larger blocks allowed a lower processing time per sample. At 23.2ms latency (1024 samples at 44.1kHz), it was possible to apply 9 second impulse responses on a standard laptop computer.
Download A Wave Digital Filter Model of the Fairchild 670 Limiter This paper presents a circuit-based, digital model of the prized 1950’s vintage Fairchild R 670 vacuum tube limiter. The model uses a mixture of black boxes and wave digital filters, as a step toward a fully wave digital filter design. Wave digital filters provide an efficient, modular way to digitally simulate analog circuits. A novel model for the 6386 triode is introduced to simulate the active component in a wave digital filter model of the Fairchild 670’s signal amplifier. The signal amplifier is integrated with a hybrid wave digital filter/black-box sidechain amplifier model to form a complete model of the Fairchild 670. Model test results for music and pure tones are discussed, highlighting the device’s static gain characteristics and gain reduction dependent distortion. Finally, this paper discusses the model’s salient features and their implications for designing dynamics processors.
Download A jump start for NMF with N-FINDR and NNLS Nonnegative Matrix Factorization is a popular tool for the analysis of audio spectrograms. It is usually initialized with random data, after which it iteratively converges to a local optimum. In this paper we show that N-FINDR and NNLS, popular techniques for dictionary and activation matrix learning in remote sensing, prove useful to create a better starting point for NMF. This reduces the number of iterations necessary to come to a decomposition of similar quality. Adapting algorithms from the hyperspectral image unmixing and remote sensing communities, provides an interesting direction for future research in audio spectrogram factorization.
Download Simulating Microphone Bleed and Tom-tom Resonance in Multisampled Drum Workstations In recent years multisampled drum workstations have become increasingly popular. They offer an alternative to recording a full drum kit if a producer, engineer or amateur lacks the equipment, money, space or knowledge to produce a quality recording. These drum workstations strive for realism, often recording up to a hundred different velocity hits of the same drum, including recordings from all microphones for each drum hit and including bleed between these microphones. This paper describes research undertaken to investigate if it is possible to simulate the snare and kick drum bleed into the tom-tom microphones and the subsequent resonance of the tom-tom that is caused, with the aim of reducing the amount of audio data that needs to be stored. A listening test was performed asking participants to identify the real recording from a simulation. The results were not statistically significant to reject the hypothesis that subjects were unable to distinguish the difference between the real and simulated recordings. This suggests listeners were unable to identify the real recording in the majority of cases.
Download Visualization of Signals and Algorithms in Kronos Kronos is a visual-oriented programming language and a compiler aimed at musical signal processing tasks. Its distinctive feature is the support for functional programming idioms like closures and higher order functions in the context of high performance real time DSP. This paper examines the visual aspect of the system. The programming user interface is discussed, along with a scheme for building custom data visualization algorithms inside the system.
Download Practical Empirical Mode Decomposition For Audio Synthesis A new method of Synthesis by Analysis for multi-component signals of fast changing instantaneous attributes is introduced. It makes use of two recent developments for signal decomposition to obtain near mono-component signals whose instantaneous attributes can be used for synthesis. Furthermore, by extension and combination of both decomposition methods, the overall quality of the decomposition is shown to improve considerably.