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Home » Archives for Dimitra Vergyri
Dimitra Vergyri

Dimitra Vergyri

Director, Speech Technology and Research Laboratory (STAR)
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Publications

Information & computer science publications April 17, 2020

Speech‐based markers for post traumatic stress disorder in US veterans

Andreas Tsiartas, Colleen Richey, Jennifer Smith, Bruce Knoth, Dimitra Vergyri

This study demonstrates that a speech-based algorithm can objectively differentiate PTSD cases from controls.

Speech & natural language publications December 1, 2017 Conference Proceeding

Tackling Unseen Acoustic Conditions in Query-by-Example Search Using Time and Frequency Convolution for Multilingual Deep Bottleneck Features

Horacio Franco, Dimitra Vergyri

Standard keyword spotting based on Automatic Speech Recognition (ASR) cannot be used on low- and no-resource languages due to lack of annotated data and/or linguistic resources.  In recent years, query-by-example (QbE) has emerged as an alternate way to enroll and find spoken queries in large audio corpora,  yet  mismatched  and  unseen  acoustic  conditions  remain a  difficult  challenge  given  the  lack  of  enrollment  data.  This paper revisits two neural network architectures developed for noise  and  channel-robust  ASR,  and  applies  them  to  building a  state-of-art  multilingual  QbE  system.   By  applying  convolution in time or frequency across the spectrum, those convolutional bottlenecks learn more discriminative deep bottleneck features.  In conjunction with dynamic time warping (DTW), these features enable robust QbE systems.  We use the MediaEval 2014 QUESST data to evaluate robustness against language  and  channel  mismatches,  and  add  several  levels  of  artificial  noise  to  the  data  to  evaluate  performance  in  degraded acoustic environments.  We also assess performance on an Air Traffic Control QbE task with more realistic and higher levels of distortion in the push-to-talk domain.

Speech & natural language publications March 1, 2017 Conference Proceeding

Speech recognition in unseen and noisy channel conditions

Horacio Franco, Martin Graciarena, Dimitra Vergyri

Speech recognition in varying background conditions is a challenging problem. Acoustic condition mismatch between training and evaluation data can significantly reduce recognition performance. For mismatched conditions, data-adaptation techniques are typically found to be useful, as they expose the acoustic model to the new data condition(s). Supervised adaptation techniques usually provide substantial performance improvement, but such gain is contingent on having labeled or transcribed data, which is often unavailable. The alternative is unsupervised adaptation, where feature-transform methods and model-adaptation techniques are typically explored. This work investigates robust features, feature-space maximum likelihood linear regression (fMLLR) transform, and deep convolutional nets to address the problem of unseen channel and noise conditions. In addition, the work investigates bottleneck (BN) features extracted from deep autoencoder (DAE) networks trained by using acoustic features extracted from the speech signal. We demonstrate that such representations not only produce robust systems but also that they can be used to perform data selection for unsupervised model adaptation. Our results indicate that the techniques presented in this paper significantly improve performance of speech recognition systems in unseen channel and noise conditions.

Speech & natural language publications March 1, 2017 Conference Proceeding

Toward human-assisted lexical unit discovery without text resources

Andreas Kathol, Dimitra Vergyri, Harry Bratt

This work addresses lexical unit discovery for languages without (usable) written resources. Previous work has addressed this problem using entirely unsupervised methodologies.  Our approach in contrast investigates the use of linguistic and speaker knowledge which are often available even if text resources are not.  We create a framework that benefits from such resources, not assuming orthographic representations and avoiding generation of word-level transcriptions.  We adapt a universal phone recognizer to the target language and use it to convert audio into a searchable phone string for lexical unit discovery via fuzzy sub-string matching.  Linguistic knowledge is used to constrain phone recognition output and to constrain lexical unit discovery on the phone recognizer output.
Target language speakers are used to assist a linguist in creating phonetic transcriptions for the adaptation of acoustic and language models, by respeaking more clearly a small portion of the target language audio.  We also explore robust features and feature transform through deep auto-encoders for better phone recognition performance.
The proposed approach achieves lexical unit discovery performance comparable to state-of-the-art zero-resource methods.  Since the system is built on phonetic recognition, discovered units are immediately interpretable.  They can be used to automatically populate a pronunciation lexicon and enable iterative improvement through additional feedback from target language speakers.

Speech & natural language publications March 1, 2017 Conference Proceeding

Joint modeling of articulatory and acoustic spaces for continuous speech recognition tasks

Dimitra Vergyri, Horacio Franco

Articulatory information can effectively model variability in speech and can improve speech recognition performance under varying acoustic conditions.  Learning speaker-independent articulatory models has always been challenging, as speaker-specific information in the articulatory and acoustic spaces increases the complexity of the speech-to-articulatory space inverse modeling, which is already an ill-posed problem due to its inherent nonlinearity and  non-uniqueness.  This  paper  investigates using deep neural networks (DNN) and convolutional neural networks (CNNs) for mapping speech data into its corresponding articulatory space.  Our results indicate that the CNN models perform better than their DNN counterparts for speech inversion.  In addition, we used the inverse models to generate articulatory trajectories from speech for three different standard speech recognition tasks.  To effectively model the articulatory features’ temporal modulations while retaining the acoustic features’ spatiotemporal signatures, we explored a joint modeling strategy to simultaneously learn both the acoustic and articulatory spaces.  The results from multiple speech recognition tasks indicate that articulatory features can improve recognition performance when the acoustic and articulatory spaces are jointly learned with one common objective function.

Speech & natural language publications September 1, 2016 Conference Paper

Fusion Strategies for Robust Speech Recognition and Keyword Spotting for Channel- and Noise-Degraded Speech

Dimitra Vergyri

Current state-of-the-art automatic speech recognition systems are sensitive to changing acoustic conditions, which can cause significant performance degradation.

Speech & natural language publications September 1, 2016 Conference Paper

Unsupervised Learning of Acoustic Units Using Autoencoders and Kohonen Nets

Dimitra Vergyri, Horacio Franco

Often, prior knowledge of subword units is unavailable for low-resource languages. Instead, a global subword unit description, such as a universal phone set, is typically used in such scenarios. One major bottleneck for existing speech-processing systems is their reliance on transcriptions. Unfortunately, the preponderance of data becoming available everyday is only worsening the problem, as properly transcribing, and hence making this data useful for training speech-processing models, is impossible. This work investigates learning acoustic units in an unsupervised manner from real-world speech data by using a cascade of an autoencoder and a Kohonen net. For this purpose, a deep autoencoder with a bottleneck layer at the center was trained with multiple languages. Once trained, the bottleneck-layer output was used to train a Kohonen net, such that state-level ids can be assigned to the bottleneck outputs. To ascertain how consistent such state-level ids are with respect to the acoustic units, phone-alignment information was used for a part of the data to qualify if indeed a functional relationship existed between the phone ids and the Kohonen state ids and, if yes, whether such relationship can be generalized to data that are not transcribed.

Speech & natural language publications December 1, 2015 Conference Paper

Improving robustness against reverberation for automatic speech recognition

Mitchell McLaren, Martin Graciarena, Horacio Franco, Dimitra Vergyri

In this work, we explore the role of robust acoustic features motivated by human speech perception studies, for building ASR systems robust to reverberation effects.

Speech & natural language publications September 1, 2015 Conference Paper

Speech-based assessment of PTSD in a military population using diverse feature classes

Bruce Knoth, Dimitra Vergyri, Mitchell McLaren

We analyzed recordings of the Clinician-Administered PTSD Scale (CAPS) interview from military personnel diagnosed as PTSD positive versus negative.

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