Download Automatic Target Mixing using Least-Squares Optimization of Gains and Equalization Settings The proposed automatic target mixing algorithm determines the gains and the equalization settings for the mixing of a multi-track recording using a least-squares optimization. These parameters are estimated using a single channel target mix, that is a signal which contains the same audio tracks as the multi-track recording, but that has been previously mixed using some unknown settings. Several tests have been done in order to evaluate the performances of two different approaches to the optimization, namely the sub-band estimator and the FIR filters estimator. The results show that, using the latter technique, the proposed algorithm is able to retrieve the parameters originally applied to the target mix. This achievement can be useful for remastering applications, where both the original recording sessions and the final mix are available, but there is the need to retrieve the mixing parameters originally applied to the various audio tracks.
Download Self-Authentication of Audio signals by Chirp Coding This paper discusses a new approach to ‘watermarking’ digital signals using linear frequency modulated or ‘chirp’ coding. The principles underlying this approach are based on the use of a matched filter to provide a reconstruction of a chirped code that is uniquely robust in the case of signals with very low signal-to-noise ratios. Chirp coding for authenticating data is generic in the sense that it can be used for a range of data types and applications (the authentication of speech and audio signals, for example). The theoretical and computational aspects of the matched filter and the properties of a chirp are revisited to provide the essential background to the method. Signal code generating schemes are then addressed and details of the coding and decoding techniques considered. Finally, the paper briefly describes an example application which is available on-line for readers who are interested in using the approach for audio data authentication working with either WAV or MP3 files.
Download Adaptive Phase Distortion Synthesis This article discusses Phase Distortion synthesis and its application to arbitrary input signals. The main elements that compose the technique are presented. Its similarities to Phase Modulation are discussed and the equivalence between the two techniques is explored. Two alternative methods of distorting the phase of an arbitrary signal are presented. The first is based on the audio-rate modulation of a first-order allpass filter coefficient. The other method relies on a re-casting of the Phase Modulation equation, which leads to a heterodyned form of waveshaping. The relationship of these implementations to the original technique is explored in detail. Complementing the article, a number of examples are discussed, demonstrating the application of the technique as an interesting digital audio effect.
Download A Modular Percussion Synthesis Environment The construction of new virtual instruments is one long-term goal of physical modeling synthesis; a common strategy across various different physical modeling methodologies, including lumped network models, modal synthesis and scattering based methods, is to provide a canonical set of basic elements, and allow the user to build an instrument via certain specified connection rules. Such an environment may be described as modular. Percussion instruments form a good test-bed for the development of modular synthesis techniques—the basic components are bars and plates, and may be accompanied by connection elements, with a nonlinear character. Modular synthesis has been approached using all of the techniques mentioned above, but time domain finite difference schemes are an alternative, allowing many problems inherent in the above methods, including computability, large memory and precomputation requirements, and lack of extensibility to more complex systems, to be circumvented. One such network model is presented here along with the associated difference schemes, followed by a discussion of implementation details, the issues of excitation and output, and a description of various instrument configurations. The article concludes with a presentation of simulation results, generated in the Matlab prototyping language.
Download Five Variations on a Feedback Theme This is a study on a set of feedback amplitude modulation oscillator equations. It is based on a very simple and inexpensive algorithm which is capable of generating a complex spectrum from a sinusoidal input. We examine the original and five variations on it, discussing the details of each synthesis method. These include the addition of extra delay terms, waveshaping of the feedback signal, further heterodyning and increasing the loop delay. In complement, we provide a software implementation of these algorithms as a practical example of their application and as demonstration of their potential for synthesis instrument design.
Download Physically-based synthesis of nonlinear circular membranes This paper investigates the properties of a recently proposed physical model of nonlinear tension modulation effects in a struck circular membrane. The model simulates dynamic variations of tension (and consequently of partial frequencies) due to membrane stretching during oscillation, and is based on a more general theory of geometric nonlinearities in elastic plates. The ability of the nonlinear membrane model to simulate real-world acoustic phenomena is assessed here through resynthesis of recorded membrane (rototom) sounds. The effects of air loading and tension modulation in the recorded sounds are analyzed, and model parameters for resynthesis are consequently estimated. The example reported in the paper show that the model is able to accurately simulate the analyzed rototom sounds.
Download Inverting the Clarinet Physical-modelling based sound resynthesis is considered by estimating physical model parameters for a clarinet-like system. Having as a starting point the pressure and flow signals in the mouthpiece, a two-stage optimisation routine is employed, in order to estimate a set of physical model parameters that can be used to resynthesise the original sound. Tested on numerically generated signals, the presented inverse-modelling method can almost entirely resynthesise the input sound. For signals measured under real playing conditions, captured by three microphones embedded in the instrument bore, the pressure can be successfully reproduced, while uncertainties in the fluid dynamical behaviour reveal that further model refinement is needed to reproduce the flow in the mouthpiece.
Download Principal Component Analysis of Rasterised Audio for Cross-Synthesis This paper describes a system for cross synthesis of rasterised time-domain audio. Rasterisation of the audio allows alignment of the macroscopic features of audio samples of instrument tones prior to principal component analysis (PCA). Specifically a novel algorithm for straightening and aligning rastogram features has been developed which is based on an interactive process incorporating the Canny detection algorithm and variable resampling. Timbral cross-synthesis is achieved by projecting a given instrument tone onto the principal components derived from a training set of sounds for a different tone. The alignment algorithm improves the efficiency of PCA for resynthesizing tones.
Download New Method for Analysis and Modeling of Nonlinear Audio Systems In this paper a new method for analysis and modeling of nonlinear audio systems is presented. The method is based on swept-sine excitation signal and nonlinear convolution firstly presented in [1, 2]. It can be used in nonlinear processing for audio applications, to simulate analog nonlinear effects (distortion effects, limiters) in digital domain.