13 research outputs found

    Understanding the acoustic implications of digital transmission on fricatives

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    The aim of this thesis is to provide a better understanding of the acoustic implications of digital transmission on fricatives relevant across research fields. This is motivated by the increasing amount of digital transmitted speech across the world, and the limited knowledge on the effects of digital transmission on consonants. The thesis investigates the fricatives /f/, /Ξ/, /s/, /ʃ/, /z/, /Ă°/ and [fj]. Fricatives were expected to be particularly affected by codec compression because of their noise-like and aperiodic structure, which might be mistaken for noise by the codecs. The thesis investigates the effects of the AMR-WB-, Opus-, and MP3 codec using three different bitrates and in live transmission. The acoustic implications were measured as the first four spectral moments, peak frequency, and via spectrographic analysis. These measures were compared between baseline uncompressed WAV files and each of the codec compressed versions. This resulted in three studies. The first two are in controlled conditions i.e. the WAV files are codec compressed via a computer, whereas the third study is live with the speech transmitted between two mobile phones with and without background noise. The findings indicate significant effects of the codec compressions on the spectral measures with segment, codec and bitrate dependent tendencies. The live transmission and background noise generally produced larger effects than the controlled conditions. Intensity played a key role in the magnitude of the effects of the codec compressions and live transmission. This has implications when using codec compressed speech as data, but especially in socio- and forensic phonetics with possible diffusion of sound changes and speaker comparisons. In addition, the results have implications beyond linguistics e.g. in psychology, where clarity of speech plays a role in perceived charisma, and in hearing aid and cochlear implant technology, which both approach speech digitally and incorporate noise reduction

    Predicting the effect of home Wi-Fi quality on QoE: Extended Technical Report

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    Poor Wi-Fi quality can disrupt home users' internet experience, or the Quality of Experience (QoE). Detecting when Wi-Fi degrades QoE is extremely valuable for residential Internet Service Providers (ISPs) as home users often hold the ISP responsible whenever QoE degrades. Yet, ISPs have little visibility within the home to assist users. Our goal is to develop a system that runs on commodity access points (APs) to assist ISPs in detecting when Wi-Fi degrades QoE. Our first contribution is to develop a method to detect instances of poor QoE based on the passive observation of Wi-Fi quality metrics available in commodity APs (e.g., PHY rate). We use support vector regression to build predictors of QoE given Wi-Fi quality for popular internet applications. We then use K-means clustering to combine per-application predictors to identify regions of Wi-Fi quality where QoE is poor across applications. We call samples in these regions as poor QoE samples. Our second contribution is to apply our predictors to Wi-Fi metrics collected over one month from 3479 APs of customers of a large residential ISP. Our results show that QoE is good most of the time, still we find 11.6% of poor QoE samples. Worse, approximately 21% of stations have more than 25% poor QoE samples. In some cases, we estimate that Wi-Fi quality causes poor QoE for many hours, though in most cases poor QoE events are short

    Statistical pattern recognition for audio-forensics : empirical investigations on the application scenarios audio steganalysis and microphone forensics

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    Magdeburg, Univ., Fak. fĂŒr Informatik, Diss., 2013von Christian KrĂ€tze

    Tagungsband der 12. Tagung Phonetik und Phonologie im deutschsprachigen Raum

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    Determination of bit-rate adaptation thresholds for the opus codec for VoIP services

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    In this paper, we present an experimental evaluation of the recently standardized Opus codec used in a VoIP context. Opus operates in both narrow and wideband modes, similar to Adaptive Multi-Rate (AMR). Through the use of the Wideband Perceptual Evaluation of Speech Quality (WB-PESQ) metric, we have conducted an extensive set of experiments using multiple audio samples encoded at different bit-rates, to investigate the impact of packet loss on resulting speech quality. Using these results, fitting functions for each bit-rate were computed to provide a straightforward manner of evaluating speech quality when given a specified packet loss rate. Using ns-2, a simulation analysis was conducted to evaluate the effect of background traffic on transmitted Opus streams. We observed that, when using different levels of background traffic, the observed packet loss rates varied heavily depending on the stream bit-rate. By correlating this information with the fitting functions derived previously, we were able to define switching thresholds. These are points where the speech quality of a lower bit-rate stream is greater than that of a higher bit-rate stream for the same levels of link bandwidth saturation

    An Introduction to Computer Networks

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    An open textbook for undergraduate and graduate courses on computer networks

    Mobile Ad-Hoc Networks

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    Being infrastructure-less and without central administration control, wireless ad-hoc networking is playing a more and more important role in extending the coverage of traditional wireless infrastructure (cellular networks, wireless LAN, etc). This book includes state-of-the-art techniques and solutions for wireless ad-hoc networks. It focuses on the following topics in ad-hoc networks: quality-of-service and video communication, routing protocol and cross-layer design. A few interesting problems about security and delay-tolerant networks are also discussed. This book is targeted to provide network engineers and researchers with design guidelines for large scale wireless ad hoc networks
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