Download Fast implementation for non-linear time-scaling of stereo signals
In this paper we present an improved implementation of Duxbury’s adaptive phase-vocoder approach for audio time-stretching using non-linear time-scaling and temporal masked phase locking at transients . We show that the previous algorithm has some limitations, notably its slow implementation and its incapacity to deal with stereo signals. We propose solutions to this problems including: an improved transient detection, a much faster implementation using the IFFT for re-synthesis and a method for stretching stereo signals without artifacts. Finally, we provide some graphical results and quantitative measures to illustrate our improvements.
Download Error Compensation in Modeling Time-Varying Sinusoids
In this article we propose a method to improve the accuracy of sinusoid modeling by introducing parameter variation models into both the analyzer and the synthesizer. Using the least-square-error estimator as an example, we show how the sinusoidal parameters estimated under a stationary assumption relate to the real nonstationary process, and propose a way to reestimate the parameters using some parameter variation model. For the synthesizer, we interpolate the parameters using the same model, with the phase unwrapping process reformulated to adapt to the change. Results show that the method effectively cuts down the systematic error of a conventional system based on a least-square-error estimator and the McAulay-Quatieri synthesizer.
Download Sinusoid Modeling in a Harmonic Context
This article discusses harmonic sinusoid modeling. Unlike standard sinusoid analyzers, the harmonic sinusoid analyzer keeps close watch on partial harmony from an early stage of modeling, therefore guarantees the harmonic relationship among the sinusoids. The key element in harmonic sinusoid modeling is the harmonic sinusoid particle, which can be found by grouping short-time sinusoids. Instead of tracking short-time sinusoids, the harmonic tracker operates on harmonic particles directly. To express harmonic partial frequencies in a compact and robust form, we have developed an inequality-based representation with adjustable tolerance on frequency errors and inharmonicity, which is used in both the grouping and tracking stages. Frequency and amplitude continuity criteria are considered for tracking purpose. Numerical simulations are performed on simple synthesized signals.
Download Statistical Measures of Early Reflections of Room Impulse Responses
An impulse response of an enclosed reverberant space is composed of three basic components: the direct sound, early reflections and late reverberation. While the direct sound is a single event that can be easily identified, the division between the early reflections and late reverberation is less obvious as there is a gradual transition between the two. This paper explores two statistical measures that can aid in determining a point in time where the early reflections have transitioned into late reverberation. These metrics exploit the similarities between late reverberation and Gaussian noise that are not commonly found in early reflections. Unlike other measures, these need no prior knowledge about the rooms such as geometry or volume.
Download 3D interactive environment for music collection navigation
Previous interfaces for large collections of music have used spatial audio to enhance the presentation of a visual interface or to add a mode of interaction. An interface using only audio information is presented here as a means to explore a large music collection in a two or three-dimensional space. By taking advantage of Ambisonics and binaural technology, the application presented here can scale to large collections, have flexible playback requirements, and can be optimized for slower computers. User evaluation reveals issues in creating an intuitive mapping between between user movements in physical space and virtual movement through the collection, but the novel presentation of the music collection has positive feedback and warrants further development.
Download Notes on Model-Based Non-Sationary Sinusoid Estimation Methods Using Derivatives
This paper reviews the derivative method and explores its capacity for estimating time-varying sinusoids of complicated parameter variations. The method is reformulated on a generalized signal model. We show that under certain arrangements the estimation task becomes solving a linear system, whose coefficients can be computed from discrete samples using an integration-by-parts technique. Previous derivative and reassignment methods are shown to be special cases of this generic method. We include a discussion on the continuity criterion of window design for the derivative method. The effectiveness of the method and the window design criterion are confirmed by test results. We also show that, thanks to the generalization, off-model sinusoids can be approximated by the derivative method with a sufficiently flexible model setting.
Download Novel methods in Information Management for Advanced Audio Workflows
This paper discusses architectural aspects of a software library for unified metadata management in audio processing applications. The data incorporates editorial, production, acoustical and musicological features for a variety of use cases, ranging from adaptive audio effects to alternative metadata based visualisation. Our system is designed to capture information, prescribed by modular ontology schema. This advocates the development of intelligent user interfaces and advanced media workflows in music production environments. In an effort to reach these goals, we argue for the need of modularity and interoperable semantics in representing information. We discuss the advantages of extensible Semantic Web ontologies as opposed to using specialised but disharmonious metadata formats. Concepts and techniques permitting seamless integration with existing audio production software are described in detail.
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 On comparison of phase alignments of harmonic components
This paper provides a method for comparing phase angles of harmonic sound sources. In particular, we propose an algorithm for decomposing the difference between two sets of phases into a harmonic part, which represents the phase progress of harmonic components, and a residue part, which represents all causes of deviations from perfect harmonicity. This decomposition allows us to compare phase alignments regardless of an arbitrary time shift, and handle harmonic and noise/inharmonic parts of the phase angle separately to improve existing algorithms that handles harmonic sound sources using phase measurements. These benefits are demonstrated with a new phase-based pitch marking algorithm and an improved time-scale and pitch modification scheme using traditional harmonic sinusoidal modelling.