Joseph Timoney

A robust audio watermarking scheme based on reduced singular value decomposition and distortion removal

This paper presents a blind audio watermarking algorithm based on the reduced singular value decomposition (RSVD). A new observation on one of the resulting unitary matrices is uncovered. The proposed scheme manipulates coefficients based on this observation in order to embed watermark bits. To preserve audio fidelity a threshold-based distortion control technique is applied and this is further supplemented by distortion suppression utilizing psychoacoustic principles. Test results on real music signals show that this watermarking scheme is in the range of imperceptibility for human hearing, is accurate and also robust against MP3 compression at various bit rates as well as other selected attacks. The data payload is comparatively high compared to existing audio watermarking schemes.

The generation of natural-synthetic spectra by means of adaptive frequency modulation

Frequency-modulation (FM) synthesis is widely known as a computationally efficient method for synthesizing musically interesting timbres. However, it has suffered from neglect owing to the difficulty in creating natural-sounding spectra and mapping gestural input to synthesis parameters. Recently, a revival has occurred with the advent of adaptive audio-processing methods, and this work proposes a technique called adaptive FM synthesis. This article derives two novel ways by which an arbitrary input signal can be used to modulate a carrier. We show how phase modulation (PM) can be achieved first by using delay lines and then by heterodyning. By applying these techniques to real-world signals, it is possible to generate transitions between natural-sounding and synthesizerlike sounds. Examples are provided of the spectral consequences of adaptive FM synthesis using inputs of various acoustic instruments and a voice. An assessment of the timbral quality of synthesized sounds demonstrates its effectiveness.

New perspectives on distortion synthesis for virtual analog oscillators

��� The term “virtual analog” (VA) first appeared in the 1990s with the commercial introduction of digital synthesizer instruments that were intended to emulate the earlier analog subtractive synthesizers, such as those produced by, among others, Moog or Sequential Circuits (Smith 2008). In creating a “virtual analog” digital model, two approaches are possible: the first is to build an explicit digital model derived from the various electrical components that form the original analog circuit; the second is to use digital processing structures that will produce outputs that mimic those of the analog system. To date, the second approach has been used for the implementation of the elements of virtual analog subtractive synthesizers, as real-time computational constraints limit the efficacy of circuit models in usable software instruments (Civolani and Fontana 2008). Among the features of a subtractive synthesis system, one aspect that has received more attention than others is algorithms for real-time digital generation of the periodic waveforms associated with voltage-controlled oscillators (VCO), such as sawtooths, square waves, and triangle waves, also known as the classic analog waveforms (Stilson 2006).

Real-time detection of musical onsets with linear prediction and sinusoidal modeling

Real-time musical note onset detection plays a vital role in many audio analysis processes, such as score following, beat detection and various sound synthesis by analysis methods. This article provides a review of some of the most commonly used techniques for real-time onset detection. We suggest ways to improve these techniques by incorporating linear prediction as well as presenting a novel algorithm for real-time onset detection using sinusoidal modelling. We provide comprehensive results for both the detection accuracy and the computational performance of all of the described techniques, evaluated using Modal, our new open source library for musical onset detection, which comes with a free database of samples with hand-labelled note onsets.

Spectrally rich phase distortion sound synthesis using an allpass filter

This paper examines a recently introduced technique for sound synthesis that uses a coefficient modulated allpass filter to cause phase modifications to its input signal. The intention in this work is to outline some of the properties of the coefficient modulated allpass filter and then to establish a connection between this new method and the older technique of Phase Distortion. Results are presented to demonstrate how the allpass technique provides a spectrally richer output signal.

Measuring perceptual centers using the phase correction response

The perceptual center (P-center) is fundamental to the timing of heterogeneous event sequences, including music and speech. Unfortunately, there is currently no comprehensive and reliable model of P-centers in acoustic events, so P-centers must instead be measured empirically. This study reviews existing measurement methods and evaluates two methods in detail—the rhythm adjustment method and a new method based on the phase correction response (PCR) in a synchronous tapping task. The two methods yielded consistent P-center estimates and showed no evidence of P-center context dependence. The PCR method appears promising because it is accurate and efficient and does not require explicit perceptual judgments. As a secondary result, the magnitude of the PCR is shown to vary systematically with the onset complexity of speech sounds, which presumably reflects the perceived clarity of a sound’s P-center.

Feedback Amplitude Modulation Synthesis

A recently rediscovered sound synthesis method, which is based on feedback amplitude modulation (FBAM), is investigated. The FBAM system is interpreted as a periodically linear time-varying digital filter, and its stability, aliasing, and scaling properties are considered. Several novel variations of the basic system are derived and analyzed. Separation of the input and the modulation signals in FBAM structures is proposed which helps to create modular sound synthesis and digital audio effects applications. The FBAM is shown to be a powerful and versatile sound synthesis principle, which has similarities to the established distortion synthesis methods, but which is also essentially different from them.

Discrete-time modelling of the moog sawtooth oscillator waveform

Discrete-time modelling strategies of analogue Moog sawtooth oscillator waveforms are presented. Two alternative approaches suitable for real-time implementation are proposed, one modelling the analogue waveform in time domain using phase distortion synthesis and another matching the spectrum of an existing antialiasing sawtooth oscillator to the corresponding analogue spectrum using a first-order IIR post-equalising filter. A parameter estimation procedure for both approaches is explained and performed. Performance evaluation using polynomial fits for the estimated parameters is carried out, and good matches between the model outputs and recorded waveforms are obtained. The best match of the tested algorithms is produced by the phase distortion model and by post-equalising the fourth-order B-spline bandlimited step function sawtooth oscillator.

A Novel Audio Watermarking Algorithm Based on Reduced Singular Value Decomposition

This paper presents a transparent and accurate semi-blind audio watermarking algorithm, based on the Reduced Singular Value Decomposition (RSVD). The proposed scheme manipulates coefficients of one of the resulting unitary matrices for embedding watermark bits. To preserve audio fidelity a threshold-based distortion control technique is given. Test results on real music signals show that this watermarking scheme is transparent, accurate and robust against MP3 compression.

Experiences in Software Testing Education: Some Observations from an International Cooperation

This paper examines the outcomes of teaching a course in software testing in Ireland and China over a two-year period. In both institutions the delivery of the course is constrained to two-week duration. The learning objectives for this course are explained. The outcomes of the courses in terms of student learning are compared and analyzed. A number of observations are made that lead to recommendations as to how the educational experience can be improved for the students in both countries.