Download On the Use of Sums of Sines in the Design of Signal Windows Windowing of discrete signals by temporal weighting is an essential tool for spectral analysis and processing to reduce bias effects. Many popular weighting functions (e. g. Hann, Hamming, Blackman) are based on a sum of scaled cosines. This paper presents an alternative class of windows, constructed using sums of sines and exhibiting unique spectral behavior with regard to zero location and a side lobe decay of at least –12 dB/octave due to guaranteed continuity of the weighting. The parameters for the 2- and 3-term realizations with minimum peak side lobe level are provided. Usage of the sum-of-sines windows with the DFT and their adoption to lapped transforms such as the MDCT are also examined.
Download Harmonize-Decompose Audio Signals with Global Amplitude and Frequency Modulations A key building block in music transcription and indexing operations is the decomposition of music signals into notes. We model a note signal as a periodic signal with slow (frequency-selective) amplitude modulation and global frequency-warping. Global frequency-warping allows for an inharmonic frequency modulation, while the global amplitude modulation allows the various harmonics of the periodic signal to decay at different speeds. The global frequency-warping is achieved by a Laguerre transform (that has shown to fit stiffed strings inharmonic behavior). Assuming additive noise, the estimation of the model parameters and the optimization is performed in a Harmonize-Extract fashion. Simulations illustrate that the extraction technique oversteps the limitation of the global AM-FM representation and analysis techniques and allows the processing of inharmonic string instruments (e.g. piano).
Download A Model of Partial Tracks for Tension-Modulated Steel-String Guitar Tones This paper introduces a spectral model for plucked, steel string tones, based on functional models for time-varying fundamental frequency and inharmonicity coefficient. Techniques to evaluate those analytical values at different time indexes are reviewed and commented. A method to evaluate the unknowns of the fundamental frequency and inharmonicity coefficient functions and match the data of a given tone is presented. Frequency tracks can thereafter be deployed and traced for all values of time. Their accuracy is discussed, and applications for the model are suggested.
Download Methods for Separation of Amplitude and Frequency Modulation in Fourier Transformed Signals This paper describes methods for the removal and/or separation of amplitude and frequency modulation of individual components within a Fourier spectrum. The first proposed method has a relatively low cost and works under assumptions about the behaviour of both the local and non-local magnitude and phase of sinusoidal components for these two forms of component nonstationarity. The second method is more expensive and resynthesizes components either in the Fourier or time domain following a parameter estimation stage. Typical applications are the adjustment of expressive parameters in music signals and conditioning of signals prior to cross-synthesis.
Download Fast Signal Reconstruction from Magnitude STFT Spectrogram Based on Spectrogram Consistency The modification of magnitude spectrograms is at the core of many audio signal processing methods, from source separation to sound modification or noise canceling, and reconstructing a natural sounding signal in such situations is thus a very important issue. This article presents recent theoretical and experimental developments on the application to signal reconstruction from a modified magnitude spectrogram of the constraints that an array of complex numbers must verify to be a consistent short-time Fourier transform (STFT) spectrogram, i.e., to be the STFT spectrogram of an actual real-valued signal. We give here further theoretical insights, present several potential variations on our previously introduced algorithm, investigate various techniques to speed up the signal reconstruction process, and present a thorough experimental comparison of the performance of all the considered algorithms.
Download High-Performance Real-Time FIR-Filtering Using Fast Convolution on Graphics Hardware In this paper we examine how graphic hardware can be used for real-time FIR filtering. We implement uniformly-partitioned fast convolution in the frequency-domain and evaluate its performance on a NVIDIA GTX 285 graphics card. Motivated by audio rendering for virtual reality, our focus lies on large-scale realtime filtering with a multitude of channels, long impulse responses and low latencies. Graphics hardware has already been used for audio signal processing — including FIR and IIR filtering with respect to offline and real-time processing. However, the combination of GPU computing and real-time conditions leads to a number of challenges that have not been reviewed in detail. The new contribution of this paper is an implementation and detailled analysis of a frequency-domain fast convolution method on GPUs. We discuss specific problems that emerge under real-time conditions. Our method allows to achieve an outstanding real-time filtering performance. In this work, we do not only regard a timeinvariant filtering, but also time-varying filtering, where filters are exchanged during runtime. Furthermore, we examine the opportunities of distributed computation — using CPU and GPU — in order to maximize the performance. Finally, we identify bottlenecks and explain their impact on filter exchange latencies and update rates.
Download Self-Organised Sounds with a Tremolo Oscillator Tremolo is usually regarded as belonging to the domain of note embellishments. Rapid tremolo, taken into the audio range, is an interesting synthesis technique which is related to FM and granular synthesis. We present a tremolo oscillator, capable of a wide range of sonorities, and illustrate some of its capabilities in applications such as feature-based synthesis and sonification. A reference implementation in Csound is given. The tremolo oscillator is then put into a feedback system, where its output is subject to feature extraction, and the extracted features in turn are mapped to its control parameters. Chaotic orbits in this feedback system guarantee continuous variation, in contrast to the trivial periodic patterns that are easily obtained.
Download Digital Emulation of Distortion Effects by Wave and Phase Shaping Methods This paper will consider wave (amplitude) and phase signal shaping techniques for the digital emulation of distortion effect processing. We examine how to determine the Wave- and Phaseshaping functions with harmonic amplitude and phase data. Three distortion effects units are used to provide test data. The action of the Wave- and Phase- shaping functions derived for these effects is demonstrated with the assistance of a superresolution frequency-domain analysis technique.
Download Chebyshev Model and Synchronized Swept Sine Method in Nonlinear Audio Effect Modeling A new method for the identification of nonlinear systems, based on an input exponential swept sine signal has been proposed by Farina ten years ago. This method has been recently modified in purpose of nonlinear model estimation using a synchronized swept sine signal. It allows a robust and fast one-path analysis and identification of the unknown nonlinear system under test. In this paper this modified method is applied with Chebyshev polynomial decomposition. The combination of the Synchronized Swept Sine Method and Chebyshev polynomials leads to a nonlinear model consisting of several parallel branches, each branch containing a nonlinear Chebyshev polynomial following by a linear filter. The method is tested on an overdrive effect pedal to simulate an analog nonlinear effect in digital domain.
Download Bibliometric Study of the DAFx Proceedings 1998 - 2009 In this paper we present a bibliometric study of the Digital Audio Effects (DAFx) conference proceedings from 1998 to 2009. Using the online DAFx proceedings, we constructed a DAFx database (LaTeX) to study its bibliometric statistics in terms of research topics, growth of literature, authorship distribution, citation patterns, and frequency distribution of scientific productivity. Results showed that the DAFx literature (with quasi-linear accumulative growth) now consists of 722 contributions (including key notes, papers and posters) from 767 unique authors, from which we identified the 20 top DAFx contributors. Using Google Scholar, we identified that the top 10 most cited DAFx papers (between 43 to 65 times) are in majority (8/10) dealing with sound and music analysis (e.g. extraction of sinusoids, musical genre classification, perceived intensity of music, and musical note onset detection). This study also confirmed that the DAFx literature conforms to the Lokta’s law (n=2.0771 and C=0.6336) at 0.01 level of significance using the Kolmogorov-Smirnov test (KS-test) of goodnessof-fit. The DAFx database will serve as the basis for an Author Cocitation Analysis (ACA) and to create a DAFx conferences archive DVD.