We propose a novel approach to semi-supervised automatic speech recognition
(ASR). We first exploit a large amount of unlabeled audio data via
representation learning, where we reconstruct a temporal slice of filterbank
features from past and future context frames. The resulting deep contextualized
acoustic representations (DeCoAR) are then used to train a CTC-based end-to-end
ASR system using a smaller amount of labeled audio data. In our experiments, we
show that systems trained on DeCoAR consistently outperform ones trained on
conventional filterbank features, giving 42% and 19% relative improvement over
the baseline on WSJ eval92 and LibriSpeech test-clean, respectively. Our
approach can drastically reduce the amount of labeled data required;
unsupervised training on LibriSpeech then supervision with 100 hours of labeled
data achieves performance on par with training on all 960 hours directly.
Pre-trained models and code will be released online.

我们提出了一种新的半监督自动语音识别方法，利用表示学习从无标注音频数据中重建滤波器组特征，并使用得到的深度上下文化的声学表示训练基于 CTC 的端到端自动语音识别系统，实验表明我们的方法能够显著提高系统性能并大幅减少所需标注数据量。

深度上下文化声学表示用于半监督语音识别

Deep Contextualized Acoustic Representations For Semi-Supervised Speech  Recognition

This paper advances the design of CTC-based all-neural (or end-to-end) speech
recognizers. We propose a novel symbol inventory, and a novel iterated-CTC
method in which a second system is used to transform a noisy initial output
into a cleaner version. We present a number of stabilization and initialization
methods we have found useful in training these networks. We evaluate our system
on the commonly used NIST 2000 conversational telephony test set, and
significantly exceed the previously published performance of similar systems,
both with and without the use of an external language model and decoding
technology.

本文提出了一种基于 CTC 的全神经网络语音识别器的设计方法，包括新的符号存储库、基于迭代的 CTC 方法、稳定化方法和初始化方法等，使用 NIST 2000 会话电话测试集进行了评估，结果表明该系统明显超过了先前发布的相似系统的性能，无需使用外部语言模型和解码技术。