An investigation of the utility of monaural sound source separation via nonnegative matrix factorization applied to acoustic echo and reverberation mitigation for hands-free telephony

In this thesis we investigate the applicability and utility of Monaural Sound Source Separation (MSSS) via Nonnegative Matrix Factorization (NMF) for various problems related to audio for hands-free telephony. We first investigate MSSS via NMF as an alternative acoustic echo reduction approach to existing approaches such as Acoustic Echo Cancellation (AEC). To this end, we present the single-channel acoustic echo problem as an MSSS problem, in which the objective is to extract the users signal from a mixture also containing acoustic echo and noise. To perform separation, NMF is used to decompose the near-end microphone signal onto the union of two nonnegative bases in the magnitude Short Time Fourier Transform domain. One of these bases is for the spectral energy of the acoustic echo signal, and is formed from the in- coming far-end user’s speech, while the other basis is for the spectral energy of the near-end speaker, and is trained with speech data a priori. In comparison to AEC, the speaker extraction approach obviates Double-Talk Detection (DTD), and is demonstrated to attain its maximal echo mitigation performance immediately upon initiation and to maintain that performance during and after room changes for similar computational requirements. Speaker extraction is also shown to introduce distortion of the near-end speech signal during double-talk, which is quantified by means of a speech distortion measure and compared to that of AEC. Subsequently, we address Double-Talk Detection (DTD) for block-based AEC algorithms. We propose a novel block-based DTD algorithm that uses the available signals and the estimate of the echo signal that is produced by NMF-based speaker extraction to compute a suitably normalized correlation-based decision variable, which is compared to a fixed threshold to decide on doubletalk. Using a standard evaluation technique, the proposed algorithm is shown to have comparable detection performance to an existing conventional block-based DTD algorithm. It is also demonstrated to inherit the room change insensitivity of speaker extraction, with the proposed DTD algorithm generating minimal false doubletalk indications upon initiation and in response to room changes in comparison to the existing conventional DTD. We also show that this property allows its paired AEC to converge at a rate close to the optimum. Another focus of this thesis is the problem of inverting a single measurement of a non- minimum phase Room Impulse Response (RIR). We describe the process by which percep- tually detrimental all-pass phase distortion arises in reverberant speech filtered by the inverse of the minimum phase component of the RIR; in short, such distortion arises from inverting the magnitude response of the high-Q maximum phase zeros of the RIR. We then propose two novel partial inversion schemes that precisely mitigate this distortion. One of these schemes employs NMF-based MSSS to separate the all-pass phase distortion from the target speech in the magnitude STFT domain, while the other approach modifies the inverse minimum phase filter such that the magnitude response of the maximum phase zeros of the RIR is not fully compensated. Subjective listening tests reveal that the proposed schemes generally produce better quality output speech than a comparable inversion technique

Evaluating sleep and circadian rhythm disturbances and symptoms of impulsivity and inattention: Implications for adult attention-deficit/hyperactivity disorder

Reports of sleep disturbances and delayed sleep timing in attentiondeficit/ hyperactivity-disorder (ADHD) are common however the aetiology of such features is poorly understood. There is substantial evidence pointing to dysfunction of the circadian timing system in ADHD, and individual differences in human chronotype and diurnal preference have been linked with impulsivity and attention problems in adults. In the work presented here we examined associations between a later circadian phase of entrainment, impaired sleep quality, and circadian misalignment and how they relate to core symptoms of ADHD distributed among the general population. We report novel evidence which suggests that ‘social jetlag’ – an index of circadian misalignment arising from discordance between endogenous circadian timing and the timing of the social clock – is a consistent predictor of poorer ADHD-like symptom outcomes. Furthermore, objective assessment of the rest-activity rhythm and sleep intervals of subjects show that a failure to precisely entrain to the 24 h circadian period is associated with ADHD-like symptom severity which was in turn predicted by delayed circadian phase/sleep phase, sleep quality, and duration. Candidate gene approaches did not replicate previous findings linking symptoms of impulsivity, inattention, and later chronotype with elements of the core molecular clock. However, we did find differential susceptibility to the previously identified risk factors; poor sleep quality and social jetlag which were both modified by genotype. Preliminary data from an exploratory study examining the neurophysiological correlates of response inhibition and selective attention revealed interesting patters of ERP elicitation in individuals with high levels of social jetlag. The current findings highlight how examination of sleep and circadian rhythm disturbances associated with ADHD may inform our understanding of the disorder risk and might in the future be factored into interventions designed for better symptom management

An investigation of the utility of monaural sound source separation via nonnegative matrix factorization applied to acoustic echo and reverberation mitigation for hands-free telephony

In this thesis we investigate the applicability and utility of Monaural Sound Source Separation (MSSS) via Nonnegative Matrix Factorization (NMF) for various problems related to audio for hands-free telephony. We first investigate MSSS via NMF as an alternative acoustic echo reduction approach to existing approaches such as Acoustic Echo Cancellation (AEC). To this end, we present the single-channel acoustic echo problem as an MSSS problem, in which the objective is to extract the users signal from a mixture also containing acoustic echo and noise. To perform separation, NMF is used to decompose the near-end microphone signal onto the union of two nonnegative bases in the magnitude Short Time Fourier Transform domain. One of these bases is for the spectral energy of the acoustic echo signal, and is formed from the in- coming far-end user’s speech, while the other basis is for the spectral energy of the near-end speaker, and is trained with speech data a priori. In comparison to AEC, the speaker extraction approach obviates Double-Talk Detection (DTD), and is demonstrated to attain its maximal echo mitigation performance immediately upon initiation and to maintain that performance during and after room changes for similar computational requirements. Speaker extraction is also shown to introduce distortion of the near-end speech signal during double-talk, which is quantified by means of a speech distortion measure and compared to that of AEC. Subsequently, we address Double-Talk Detection (DTD) for block-based AEC algorithms. We propose a novel block-based DTD algorithm that uses the available signals and the estimate of the echo signal that is produced by NMF-based speaker extraction to compute a suitably normalized correlation-based decision variable, which is compared to a fixed threshold to decide on doubletalk. Using a standard evaluation technique, the proposed algorithm is shown to have comparable detection performance to an existing conventional block-based DTD algorithm. It is also demonstrated to inherit the room change insensitivity of speaker extraction, with the proposed DTD algorithm generating minimal false doubletalk indications upon initiation and in response to room changes in comparison to the existing conventional DTD. We also show that this property allows its paired AEC to converge at a rate close to the optimum. Another focus of this thesis is the problem of inverting a single measurement of a non- minimum phase Room Impulse Response (RIR). We describe the process by which percep- tually detrimental all-pass phase distortion arises in reverberant speech filtered by the inverse of the minimum phase component of the RIR; in short, such distortion arises from inverting the magnitude response of the high-Q maximum phase zeros of the RIR. We then propose two novel partial inversion schemes that precisely mitigate this distortion. One of these schemes employs NMF-based MSSS to separate the all-pass phase distortion from the target speech in the magnitude STFT domain, while the other approach modifies the inverse minimum phase filter such that the magnitude response of the maximum phase zeros of the RIR is not fully compensated. Subjective listening tests reveal that the proposed schemes generally produce better quality output speech than a comparable inversion technique

China - electronic payment services : discrimination, economic development and the GATS

First published online on April 28, 2014Revised version of EUI RSCAS WP 2013/68; Global Governance Programme-66This paper provides a legal–economic analysis of the unappealed WTO Panel Report in China – Certain Measures Affecting Electronic Payment Services (WT/DS413/R). The core issue was whether China's measures that resulted in there being only one dominant supplier of electronic payment services (EPS) in China violated the specific commitments made by China under the GATS. The panel ruled that the measures did not violate China's market access commitments because there were no explicit limitations on the entry of foreign suppliers, but that the measures were inconsistent with China's national treatment commitments in that they modified the conditions of competition in favour of domestic suppliers. This case illustrates the complexity in interpreting WTO Members’ commitments under the GATS