End-to-End Speech Recognition From the Raw Waveform

State-of-the-art speech recognition systems rely on fixed, hand-crafted features such as mel-filterbanks to preprocess the waveform before the training pipeline. In this paper, we study end-to-end systems trained directly from the raw waveform, building on two alternatives for trainable replacements of mel-filterbanks that use a convolutional architecture. The first one is inspired by gammatone filterbanks (Hoshen et al., 2015; Sainath et al, 2015), and the second one by the scattering transform (Zeghidour et al., 2017). We propose two modifications to these architectures and systematically compare them to mel-filterbanks, on the Wall Street Journal dataset. The first modification is the addition of an instance normalization layer, which greatly improves on the gammatone-based trainable filterbanks and speeds up the training of the scattering-based filterbanks. The second one relates to the low-pass filter used in these approaches. These modifications consistently improve performances for both approaches, and remove the need for a careful initialization in scattering-based trainable filterbanks. In particular, we show a consistent improvement in word error rate of the trainable filterbanks relatively to comparable mel-filterbanks. It is the first time end-to-end models trained from the raw signal significantly outperform mel-filterbanks on a large vocabulary task under clean recording conditions.Comment: Accepted for presentation at Interspeech 201

Multi-scale Alignment and Contextual History for Attention Mechanism in Sequence-to-sequence Model

A sequence-to-sequence model is a neural network module for mapping two sequences of different lengths. The sequence-to-sequence model has three core modules: encoder, decoder, and attention. Attention is the bridge that connects the encoder and decoder modules and improves model performance in many tasks. In this paper, we propose two ideas to improve sequence-to-sequence model performance by enhancing the attention module. First, we maintain the history of the location and the expected context from several previous time-steps. Second, we apply multiscale convolution from several previous attention vectors to the current decoder state. We utilized our proposed framework for sequence-to-sequence speech recognition and text-to-speech systems. The results reveal that our proposed extension could improve performance significantly compared to a standard attention baseline

Аналитический обзор интегральных систем распознавания речи

This article presents an analytic survey of various end-to-end speech recognition systems, as well as some approaches to their construction and optimization. We consider models based on connectionist temporal classification (CTC), models based on encoder-decoder architecture with attention mechanism and models using conditional random field (CRF). We also describe integration possibilities with language models at a stage of decoding. We see that such an approach significantly reduces recognition error rates for end-to-end models. A survey of research works in this subject area reveals that end-to-end systems allow achieving results close to that of the state-of-the-art hybrid models. Nevertheless, end-to-end models use simple configuration and demonstrate a high speed of learning and decoding. In addition, we consider popular frameworks and toolkits for creating speech recognition systems.Приведен аналитический обзор разновидностей интегральных (end-to-end) систем для распознавания речи, методов их построения, обучения и оптимизации. Рассмотрены варианты моделей на основе коннекционной временной классификации (CTC) в качестве функции потерь для нейронной сети, модели на основе механизма внимания и шифратор-дешифратор моделей. Также рассмотрены нейронные сети, построенные с использованием условных случайных полей (CRF), которые являются обобщением скрытых марковских моделей, что позволяет исправить многие недостатки стандартных гибридных систем распознавания речи, например, предположение о том, что элементы входных последовательностей звуков речи являются независимыми случайными величинами. Также описаны возможности интеграции с языковыми моделями на этапе декодирования, демонстрирующие существенное сокращение ошибки распознавания для интеграционных моделей. Описаны различные модификации и улучшения стандартных интегральных архитектур систем распознавания речи, как, например, обобщение коннекционной классификации и использовании регуляризации в моделях, основанных на механизмах внимания. Обзор исследований, проводимых в данной предметной области, показывает, что интегральные системы распознавания речи позволяют достичь результатов, сравнимых с результатами стандартных систем, использующих скрытые марковские модели, но с применением более простой конфигурации и быстрой работой системы распознавания как при обучении, так и при декодировании. Рассмотрены наиболее популярные и развивающиеся библиотеки и инструментарии для построения интегральных систем распознавания речи, такие как TensorFlow, Eesen, Kaldi и другие. Проведено сравнение описанных инструментариев по критериям простоты и доступности их использования для реализации интегральных систем распознавания речи

Attention-Inspired Artificial Neural Networks for Speech Processing: A Systematic Review

Artificial Neural Networks (ANNs) were created inspired by the neural networks in the human brain and have been widely applied in speech processing. The application areas of ANN include: Speech recognition, speech emotion recognition, language identification, speech enhancement, and speech separation, amongst others. Likewise, given that speech processing performed by humans involves complex cognitive processes known as auditory attention, there has been a growing amount of papers proposing ANNs supported by deep learning algorithms in conjunction with some mechanism to achieve symmetry with the human attention process. However, while these ANN approaches include attention, there is no categorization of attention integrated into the deep learning algorithms and their relation with human auditory attention. Therefore, we consider it necessary to have a review of the different ANN approaches inspired in attention to show both academic and industry experts the available models for a wide variety of applications. Based on the PRISMA methodology, we present a systematic review of the literature published since 2000, in which deep learning algorithms are applied to diverse problems related to speech processing. In this paper 133 research works are selected and the following aspects are described: (i) Most relevant features, (ii) ways in which attention has been implemented, (iii) their hypothetical relationship with human attention, and (iv) the evaluation metrics used. Additionally, the four publications most related with human attention were analyzed and their strengths and weaknesses were determined