Omilia R&D Team Contributions to Research Papers

Published on : 08-03-2019

Omilia’s R&D team comprises PhD and/or MSc holders with strong contribution to research on ASR and NLU. This is a selected list of recent publications they have co-authored with their University or Omilia as affiliation.

Speech understanding for spoken dialogue systems: From corpus harvesting to grammar rule induction. Computer Speech & Language

Iosif, E., Klasinas, I., Athanasopoulou, G., Palogiannidi, E., Georgiladakis, S., Louka, K., & Potamianos, A. (2018). Speech understanding for spoken dialogue systems: From corpus harvesting to grammar rule induction. Computer Speech & Language, 47, 272-297.

Abstract: We investigate algorithms and tools for the semi-automatic authoring of grammars for spoken dialogue systems (SDS) proposing a framework that spans from corpora creation to grammar induction algorithms. A realistic human-in-the-loop approach is followed balancing automation and human intervention to optimize cost to performance ratio for grammar development. Web harvesting is the main approach investigated for eliciting spoken dialogue textual data, while crowdsourcing is also proposed as an alternative method. Several techniques are presented for constructing web queries and filtering the acquired corpora. We also investigate how the harvested corpora can be used for the automatic and semi-automatic (human-in-the-loop) induction of grammar rules. SDS grammar rules and induction algorithms are grouped into two types, namely, low- and high-level. Two families of algorithms are investigated for rule induction: one based on semantic similarity and distributional semantic models, and the other using more traditional statistical modeling approaches (e.g., slot-filling algorithms using Conditional Random Fields). Evaluation results are presented for two domains and languages. High-level induction precision scores up to 60% are obtained. Results advocate the portability of the proposed features and algorithms across languages and domains.

View the complete paper here.

Sentiment analysis in Twitter using semantic-affective model adaptation

Palogiannidi, E., Kolovou, A., Christopoulou, F., Kokkinos, F., Iosif, E., Malandrakis, N. & Potamianos, A. (2016). Tweester at SemEval-2016 Task 4: Sentiment analysis in Twitter using semantic-affective model adaptation. In Proceedings of the 10th International Workshop on Semantic Evaluation (SemEval-2016) (pp. 155-163).

Abstract: We describe our submission to SemEval2016 Task 4: Sentiment Analysis in Twitter. The proposed system ranked first for the sub-task B. Our system comprises of multiple independent models such as neural networks, semantic-affective models and topic modeling that are combined in a probabilistic way. The novelty of the system is the employment of a topic modeling approach in order to adapt the semantic-affective space for each tweet. In addition, significant enhancements were made in the main system dealing with the data preprocessing and feature extraction including the employment of word embeddings. Each model is used to predict a tweet’s sentiment (positive, negative or neutral) and a late fusion scheme is adopted for the final decision.

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Improved Frequency Modulation Features for Multichannel Distant Speech Recognition

Rodomagoulakis, I., & Maragos, P. (2018). Improved Frequency Modulation Features for Multichannel Distant Speech Recognition. In Proceedings of IEEE ICASSP 2019.

Abstract: Frequency modulation features capture the fine structure of speech formants that constitute beneficial and supplementary to the traditional energy-based cepstral features. Improvements have been demonstrated mainly in GMM-HMM systems for small and large vocabulary tasks. Yet, they have limited applications in DNN-HMM systems and Distant Speech Recognition (DSR) tasks. Herein, we elaborate on their integration within state-of-the-art front-end schemes that include post-processing of MFCCs resulting in discriminant and speaker-adapted features of large temporal contexts. We explore 1) multichannel demodulation schemes for multi-microphone setups, 2) richer descriptors of frequency modulations, and 3) feature transformation and combination via hierarchical deep networks. We present results for tandem and hybrid recognition with GMM and DNN acoustic models, respectively. The improved modulation features are combined efficiently with MFCCs yielding modest and consistent improvements in multichannel distant speech recognition tasks on reverberant and noisy environments, where recognition rates are far from human performance.

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Multimodal Signal Processing and Learning Aspects of Human-Robot Interaction for an Assistive Bathing Robot

Zlatintsi, A., Rodomagoulakis, I., Koutras, P., Dometios, A. C., Pitsikalis, V., Tzafestas, C. S., & Maragos, P. (2018). Multimodal Signal Processing and Learning Aspects of Human-Robot Interaction for an Assistive Bathing Robot. In Proceedings of IEEE ICASSP 2018.

Abstract: We explore new aspects of assistive living on smart human-robot interaction (HRI) that involve automatic recognition and online validation of speech and gestures in a natural interface, providing social features for HRI. We introduce a whole framework and resources of a real-life scenario for elderly subjects supported by an assistive bathing robot, addressing health and hygiene care issues. We contribute a new dataset and a suite of tools used for data acquisition and a state-of-the-art pipeline for multimodal learning within the framework of the I-Support bathing robot, with emphasis on audio and RGB-D visual streams. We consider privacy issues by evaluating the depth visual stream along with the RGB, using Kinect sensors. The audio gestural recognition task on this new dataset yields up to 84.5%, while the online validation of the I-Support system on elderly users accomplishes up to 84% when the two modalities are fused together. The results are promising enough to support further research in the area of multimodal recognition for assistive social HRI, considering the difficulties of the specific task. Upon acceptance of the paper part of the data will be publicly available.

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Room-localized spoken command recognition in multi-room, multi-microphone environments

Rodomagoulakis, I., Katsamanis, A., Potamianos, G., Giannoulis, P., Tsiami, A., & Maragos, P. (2017). Room-localized spoken command recognition in multi-room, multi-microphone environments. Computer Speech & Language, 46, 419-443.

Abstract: The paper focuses on the design of a practical system pipeline for always listening, far field spoken command recognition in everyday smart indoor environments that consist of multiple rooms equipped with sparsely distributed microphone arrays. Such environments, for example domestic and multiroom offices, present challenging acoustic scenes to state of the art speech recognizers, especially under always listening operation, due to low signal to noise ratios, frequent overlaps of target speech, acoustic events, and background noise, as well as inter-room interference and reverberation. In addition, recognition of target commands often needs to be accompanied by their spatial localization, at least at the room level, to account for users in different rooms, providing command disambiguation and room-localized feedback. To address the above requirements, the use of parallel recognition pipelines is proposed, one per room of interest. The approach is enabled by a room-dependent speech activity detection module that employs appropriate multichannel features to determine speech segments and their room of origin, feeding them to the corresponding room dependent pipelines for further processing. These consist of the traditional cascade of far field spoken command detection and recognition, the former based on the detection of “activating” key phrases. Robustness to the challenging environments is pursued by a number of multichannel combination and acoustic modeling techniques, thoroughly investigated in the paper. In particular, channel selection, beamforming, and decision fusion of single-channel results are considered, with the latter performing best. Additional gains are observed, when the employed acoustic models are trained on appropriately simulated reverberant and noisy speech data, and are channel-adapted to the target environments. Further issues investigated concern the interdependencies of the various system components, demonstrating the superiority of joint optimization of the component tunable parameters over their separate or sequential optimization. The proposed approach is developed for the Greek language, exhibiting promising performance in real recordings in a four-room apartment, as well as a two-room office. For example, in the latter, a 76.6% command recognition accuracy is achieved on a speaker-independent test, employing a 180-sentence decoding grammar. This result represents a 46% relative improvement over conventional beamforming.

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Automatic Phonetic Segmentation and Pronunciation Detection with Various Approaches of Acoustic Modeling

Mizera, P., & Pollak, P. (2018, September). Automatic Phonetic Segmentation and Pronunciation Detection with Various Approaches of Acoustic Modeling. In International Conference on Speech and Computer (pp. 419-429).

Abstract: The paper describes HMM based phonetic segmentation realized by KALDI toolkit with the focus on study of accuracy of various acoustic modeling such as GMM-HMM vs. DNN-HMM, monophone vs. triphone, speaker independent vs. speaker dependent. The analysis was performed using TIMIT database and it proved the contribution of advanced acoustic modeling for the choice of a proper pronunciation variant. For this purpose, the lexicon covering the pronunciation variability among TIMIT speakers was created on the basis of phonetic transcriptions available in TIMIT corpus. When the proper sequence of phones is recognized by DNN-HMM system, more precise boundary placement can be then obtained using basic monophone acoustic models.

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Improving of LVCSR for Causal Czech Using Publicly Available Language Resources

Mizera, P., & Pollak, P. (2017, September). Improving of LVCSR for Causal Czech Using Publicly Available Language Resources. In International Conference on Speech and Computer (pp. 427-437).

Abstract: The paper presents the design of Czech casual speech recognition which is a part of the wider research focused on understanding very informal speaking styles. The study was carried out using the NCCCz corpus and the contributions of optimized acoustic and language models as well as pronunciation lexicon optimization were analyzed. Special attention was paid to the impact of publicly available corpora suitable for language model (LM) creation. Our final DNN-HMM system achieved in the task of casual speech recognition WER of 30–60% depending on LM used. The results of recognition for other speaking styles are presented as well for the comparison purposes. The system was built using KALDI toolkit and created recipes are available for the research community.

View the complete paper here.

Dithering techniques in automatic recognition of speech corrupted by MP3 compression: Analysis, solutions and experiments

Borsky, M., Mizera, P., Pollak, P., & Nouza, J. (2017). Dithering techniques in automatic recognition of speech corrupted by MP3 compression: Analysis, solutions and experiments. Speech Communication, 86, 75-84.

Abstract: A large portion of the audio files distributed over the Internet or those stored in personal and corporate media archives are in a compressed form. There exist several compression techniques and algorithms but it is the MPEG Layer-3 (known as MP3) that has achieved a really wide popularity in general audio coding, and in speech, too. However, the algorithm is lossy in nature and introduces distortion into spectral and temporal characteristics of a signal. In this paper we study its impact on automatic speech recognition (ASR). We show that with decreasing MP3 bitrates the major source of ASR performance degradation is deep spectral valleys (i.e. bins with almost zero energy) caused by the masking effect of the MP3 algorithm. We demonstrate that these unnatural gaps in spectrum can be effectively compensated by adding a certain amount of noise to the distorted signal. We provide theoretical background for this approach where we show that the added noise affects mainly the spectral valleys. They are filled by the noise while the spectral bins with speech remain almost unchanged. This helps to restore a more natural shape of log spectrum and cepstrum, and consequently has a positive impact on ASR performance. In our previous work, we have proposed two types of the signal dithering (noise addition) technique, one applied globally, the other in a more selective way. In this paper, we offer a more detailed insight into their performance. We provide results from many experiments where we test them in various scenarios, using a large vocabulary continuous speech recognition (LVCSR) system, acoustic models based on gaussian-mixture model (GMM) as well as on deep-neural network (DNN), and multiple speech databases in three languages (Czech, English and German). Our results prove that both the proposed techniques, and the selective dithering method, in particular, yield consistent compensation of the negative impact of the MP3 compressed speech on ASR performance.

View the complete paper here.

Cepstral distance based channel selection for distant speech recognition

Flores, C. G., Tryfou, G., & Omologo, M. (2018). Cepstral distance based channel selection for distant speech recognition. Computer Speech & Language, 47, 314-332.

Abstract: Shifting from a single to a multi-microphone setting, distant speech recognition can be benefited from the multiple instances of the same utterance in many ways. An effective approach, especially when microphones are not organized in an array fashion, is given by channel selection (CS), which assumes that for each utterance there is at least one channel that can improve the recognition results when compared to the decoding of the remaining channels. In order to identify this most favourable channel, a possible approach is to estimate the degree of distortion that characterizes each microphone signal. In a reverberant environment, this distortion can vary significantly across microphones, for instance due to the orientation of the speaker’s head. In this work, we investigate on the application of cepstral distance as a distortion measure that turns out to be closely related to properties of the room acoustics, such as reverberation time and direct-to-reverberant ratio. From this measure, a blind CS method is derived, which relies on a reference computed by averaging log magnitude spectra of all the microphone signals. Another aim of our study is to propose a novel methodology to analyze CS under a wide set of experimental conditions and setup variations, which depend on the sound source position, its orientation, and the microphone network configuration. Based on the use of prior information, we introduce an informed technique to predict CS performance. Experimental results show both the effectiveness of the proposed blind CS method and the value of the aforementioned analysis methodology. The experiments were conducted using different sets of real and simulated data, the latter ones derived from synthetic and from measured impulse responses. It is demonstrated that the proposed blind CS method is well related to the oracle selection of the best recognized channel. Moreover, our method outperforms a state-of-the-art one, especially on real data.

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A reassigned front-end for speech recognition

Tryfou, G., & Omologo, M. (2017). A reassigned front-end for speech recognition. In 25th European Signal Processing Conference (EUSIPCO), 2017.

Abstract: This paper introduces the use of the TFRCC features, a time-frequency reassigned feature set, as a front-end for speech recognition. Compared to the power spectrogram, the time-frequency reassigned version is particularly helpful in describing simultaneously the temporal and spectral features of speech signals, as it offers an improved visualization of the various components. This powerful attribute is exploited from the cepstral reassigned features, which are incorporated in a state-of-the-art speech recognizer. Experimental activities investigate the proposed features in various scenarios, starting from recognition of close-talk signals and gradually increasing the complexity of the task. The results prove the superiority of these features compared to a MFCC baseline.

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Channel Selection for Distant Speech Recognition Exploiting Cepstral Distance

Guerrero, C., Tryfou, G., & Omologo, M. (2016). Channel Selection for Distant Speech Recognition Exploiting Cepstral Distance. In INTERSPEECH, 2016.

Abstract: In a multi-microphone distant speech recognition task, the redundancy of information that results from the availability of multiple instances of the same source signal can be exploited through channel selection. In this work, we propose the use of cepstral distance as a means of assessment of the available channels, in an informed and a blind fashion. In the informed approach the distances between the close-talk and all of the channels are calculated. In the blind method, the cepstral distances are computed using an estimated reference signal, assumed to represent the average distortion among the available channels. Furthermore, we propose a new evaluation methodology that better illustrates the strengths and weaknesses of a channel selection method, in comparison to the sole use of word error rate. The experimental results suggest that the proposed blind method successfully selects the least distorted channel, when sufficient room coverage is provided by the microphone network. As a result, improved recognition rates are obtained in a distant speech recognition task, both in a simulated and a real context.

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Zero-shot keyword spotting for visual speech recognition in-the-wild

Stafylakis, T., & Tzimiropoulos, G. (2018). Zero-shot keyword spotting for visual speech recognition in-the-wild. In Proceedings of the European Conference on Computer Vision (ECCV), 2018.

Abstract: Visual keyword spotting (KWS) is the problem of estimating whether a text query occurs in a given recording using only video information. This paper focuses on visual KWS for words unseen during training, a real-world, practical setting which so far has received no attention by the community. To this end, we devise an end-to-end architecture comprising (a) a state-of-the-art visual feature extractor based on spatiotemporal Residual Networks, (b) a grapheme-to-phoneme model based on sequence-to-sequence neural networks, and (c) a stack of recurrent neural networks which learn how to correlate visual features with the keyword representation. Different to prior works on KWS, which try to learn word representations merely from sequences of graphemes (i.e. letters), we propose the use of a grapheme-to-phoneme encoder-decoder model which learns how to map words to their pronunciation. We demonstrate that our system obtains very promising visual-only KWS results on the challenging LRS2 database, for keywords unseen during training. We also show that our system outperforms a baseline which addresses KWS via automatic speech recognition (ASR), while it drastically improves over other recently proposed ASR-free KWS methods.

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Pushing the boundaries of audiovisual word recognition using Residual Networks and LSTMs

Stafylakis, T., Khan, M. H., & Tzimiropoulos, G. (2018). Pushing the boundaries of audiovisual word recognition using Residual Networks and LSTMs. Computer Vision and Image Understanding, 176, 22-32, 2018.

Abstract: Visual and audiovisual speech recognition are witnessing a renaissance which is largely due to the advent of deep learning methods. In this paper, we present a deep learning architecture for lipreading and audiovisual word recognition, which combines Residual Networks equipped with spatiotemporal input layers and Bidirectional LSTMs. The lipreading architecture attains 11.92% misclassification rate on the challenging Lipreading-In-The-Wild database, which is composed of excerpts from BBC-TV, each containing one of the 500 target words. Audiovisual experiments are performed using both intermediate and late integration, as well as several types and levels of environmental noise, and notable improvements over the audio-only network are reported, even in the case of clean speech. A further analysis on the utility of target word boundaries is provided, as well as on the capacity of the network in modeling the linguistic context of the target word. Finally, we examine difficult word pairs and discuss how visual information helps towards attaining higher recognition accuracy.

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Root Cause Analysis of Miscommunication Hotspots in Spoken Dialogue Systems

Georgiladakis, S., Athanasopoulou, G., Meena, R., Lopes, J., Chorianopoulou, A., Palogiannidi, E., … & Potamianos, A. (2016). Root Cause Analysis of Miscommunication Hotspots in Spoken Dialogue Systems. In INTERSPEECH 2016.

Abstract: A major challenge in Spoken Dialogue Systems (SDS) is the detection of problematic communication (hotspots), as well as the classification of these hotspots into different types (root cause analysis). In this work, we focus on two classes of root cause, namely, erroneous speech recognition vs. other (e.g., dialogue strategy). Specifically, we propose an automatic algorithm for detecting hotspots and classifying root causes in two subsequent steps. Regarding hotspot detection, various lexico-semantic features are used for capturing repetition patterns along with affective features. Lexico-semantic and repetition features are also employed for root cause analysis. Both algorithms are evaluated with respect to the Let’s Go dataset (bus information system). In terms of classification unweighted average recall, performance of 80% and 70% is achieved for hotspot detection and root cause analysis, respectively.

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Affective lexicon creation for the Greek language

Palogiannidi, E., Koutsakis, P., Losif, E., & Potamianos, A. (2016). Affective lexicon creation for the Greek language. In 10th edition of the Language Resources and Evaluation Conference (LREC 2016).

Abstract: Starting from the English affective lexicon ANEW (Bradley and Lang, 1999a) we have created the first Greek affective lexicon. It contains human ratings for the three continuous affective dimensions of valence, arousal and dominance for 1034 words. The Greek affective lexicon is compared with affective lexica in English, Spanish and Portuguese. The lexicon is automatically expanded by selecting a small number of manually annotated words to bootstrap the process of estimating affective ratings of unknown words. We experimented with the parameters of the semantic-affective model in order to investigate their impact to its performance, which reaches 85% binary classification accuracy (positive vs. negative ratings). We share the Greek affective lexicon that consists of 1034 words and the automatically expanded Greek affective lexicon that contains 407K words.

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Text-dependent speaker recognition with random digit strings

Stafylakis, T., Alam, M. J., & Kenny, P. (2016). Text-dependent speaker recognition with random digit strings. IEEE/ACM Transactions on Audio, Speech and Language Processing (TASLP), 24(7), 1194-1203.

Abstract: In this paper we explore Joint Factor Analysis (JFA) for text-dependent speaker recognition with random digit strings. The core of the proposed method is a JFA model by which we extract features. These features can either represent overall utterances or individual digits, and are fed into a trainable backend to estimate likelihood ratios. Within this framework, several extension are proposed. A first is a logistic regression method for combining log-likelihood ratios that correspond to individual mixture components. A second is the extraction of phonetically-aware Baum-Welch statistics, by using forced alignment instead of the typical posterior probabilities that are derived by the universal background model. We also explore a digit-string dependent way to apply score normalization, that exhibits a notable improvement compared to the standard one. By fusing 6 JFA features, we attained 2.01% and 3.19% Equal Error Rates, on male and female respectively, on the challenging RSR2015 (part III) dataset.

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Speaker and channel factors in text-dependent speaker recognition

Stafylakis, T., Kenny, P., Alam, M. J., & Kockmann, M. (2016). Speaker and channel factors in text-dependent speaker recognition. IEEE/ACM Transactions on Audio, Speech, and Language Processing, 24(1), 65-78.

Abstract: We reformulate Joint Factor Analysis so that it can serve as a feature extractor for text-dependent speaker recognition. The new formulation is based on left-to-right modeling with tied mixture HMMs and it is designed to deal with problems such as the inadequacy of subspace methods in modeling speaker-phrase variability, UBM mismatches that arise as a result of variable phonetic content, and the need to exploit text-independent resources in text-dependent speaker recognition. We pass the features extracted by factor analysis to a trainable backend which plays a role analogous to that of PLDA in the i-vector/PLDA cascade in text-independent speaker recognition. We evaluate these methods on a proprietary dataset consisting of English and Urdu passphrases collected in Pakistan. By using both text-independent data and text-dependent data for training purposes and by fusing results obtained with multiple front ends at the score level, we achieved equal error rates of around 1.3% and 2% on the English and Urdu portions of this task.

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