Download Timbre Morphing using the Modal Distribution We present techniques for timbre morphing between two audio signals based on the Modal distribution time-frequency representation of music signals. A signal synthesis method is described which resynthesises signals from Modal distributions. Direct resynthesis from the original signal produces a timbre that is almost indistinguishable from the source. In deciding which salient features to morph a relational graph representation of timbre is used and linear interpolation and non-linear warping are applied in performing the morph between Modal distributions.
Download Smoothing of the Control Signal without Clipped Output in Digital Peak Limiters This paper studies the reduction of nonlinearity of digital peak limiters used for maximizing signal levels. The goal is to control the time-varying gain smoothly enough to avoid frequency artifacts in the output signal. Smoother gain control is traditionally obtained by lowpass Þltering the gain or the signal envelope. However, simple Þltering causes overshoots and leads to either clipped output or non-maximal signal levels, depending on the gain applied to the limiter output. In order to obtain smooth gain control without clipping, this paper proposes an envelope detection method based on order-statistics Þltering.
Download The Sounds of the Avian Syrinx - are they Really Flute-Like? This research presents a model of the avian vocal tract, implemented using classical waveguide synthesis and numerical methods. The vocal organ of the songbird, the syrinx, has a unique topography of acoustic tubes (a trachea with a bifurcation at its base) making it a rather unique subject for waveguide synthesis. In the upper region of the two bifid bronchi lies a nonlinear vibrating membrane – the primary resonator in sound production. Unlike most reed musical instruments, the more significant displacement of the membrane is perpendicular to the directions of airflow, due to the Bernoulli effect. The model of the membrane displacement, and the resulting pressure through the constriction created by the membrane motion, is therefore derived beginning with the Bernoulli equation.
Download A Measurement Technique for Highly Nonlinear Transfer Functions This paper presents a new method to estimate nonlinear transfer functions of tube amplifiers or distortion effect stages. A special test signal and a sorting algorithm allow the calculation of the nonlinear transfer functions. PSPICE simulations of a tube amplifier as well as real-time measurements of a tube amplifier with a high quality 24bit/96kHz sound card will be presented.
Download Performance Analysis of a Source Separation Algorithm Source separation is an attractive preprocessing step for applying digital audio effects to a single source inside a signal mix. We present a performance analysis of a source separation algorithm based on time-frequency processing and its application to digital audio effects. The performance analysis gives insight to the main analysis parameters for the detection of the number of source signals inside the signal mix. We also analyze the main design parameters for the demixing operation which extracts a single source out of the signal mix.
Download Audio Signal Processing and Object-oriented Systems Object-oriented programming (OOP) has been for many years now one of the most important programming paradigms used in a variety of applications. Digital audio signal processing can benefit largely from this approach for systems development. In this paper a number of approaches to using object-orientation in audio processing systems are reviewed. Existing systems of audio processing are introduced and discussed in detail. The paper also draws attention to the different OOP techniques enabled and supported by these systems. Comparative code and tutorial examples are included, providing an insight into the development of signal processing applications using objects.
Download New SndObj Library Classes for Sinusoidal Modeling We present an object-oriented implementation for sinusoidal modelling based on the C++ Sound Object Library (SndObj). We outline the background to this analysis/synthesis technique and its inclusion in many well known methods of speech and music signal processing. Incorporation of such a well known technique into the SndObj library will enable the development of further audio processing techniques such as vocoding, time and pitch scaling and cross-synthesis on an object-oriented development platform.
Download A C++ Development Platform for Real Time Audio Processing and Synthesis Applications The computational power provided by current general purpose computers allows to undertake the implementation of low cost software-only real time audio processors. Unfortunately, computational power is not the only requirement for high demand applications. There are still important difficulties to overcome in other areas such as robustness and low latency. These difficulties have lead us to the development of Rappid, a development framework for C++ real-time high-demand audio processing applications. This paper describes the Rappid development framework. First of all we discuss the objectives we pursue with its development, and we give an overview to some other existent solutions before starting the actual description of the framework. We finally describe a first sound processing application which has been successfully developed with it.
Download Sound Effects for a Silent Computer System This paper proposes the sonification of the activity of a computer system that allows the user to monitor the basic performance parameters of the system, like CPU load, read and write activity of the hard disk or network traffic. Although, current computer systems still produce acoustic background noise, future and emerging computer systems will be more and more optimized with respect to their noise emission. In contrast to most of the concepts of auditory feedback, which present a particular sound as a feedback to a user’s command, the proposed feedback is mediated by the running computer system. The user’s interaction stimulates the system and hence the resulting feedback offers more realistic information about the current states of performance of the system. On the one hand the proposed sonification can mimic the acoustical behavior of operating components inside a computer system, while on the other hand, new qualities can be synthesized that enrich interaction with the device. Different forms of sound effects and generation for the proposed auditory feedback are realized to experiment with the usage in an environment of silent computer systems.
Download A New Criterion and Associated Bit Allocation Method for Current Audio Coding Standards This paper presents a new noise-shaping criterion. Based on the new criterion, we derive an efficient bit allocation method. The bit allocation method is applicable to the current audio standards like MPEG1 Layer 3 and MPEG4 AAC. The bit allocation method has gained a speed up for more than ten and has resulted in better quality over the traditional two nested loop method presented in ISO draft. The experiments illustrated the correction of the objective measurement criterion and the new allocation has shown the deterministic method instead of the iteration method to achieve the high allocation efficiency and best quality.