Most existing methods for audio classification assume that the vocabulary of audio classes to be classified is fixed. When novel (unseen) audio classes appear, audio classification systems need to be retrained with abundant labeled samples of all audio classes for recognizing base (initial) and novel audio classes. If novel audio classes continue to appear, the existing methods for audio classification will be inefficient and even infeasible. In this work, we propose a method for few-shot class-incremental audio classification, which can continually recognize novel audio classes without forgetting old ones. The framework of our method mainly consists of two parts: an embedding extractor and a classifier, and their constructions are decoupled. The embedding extractor is the backbone of a ResNet based network, which is frozen after construction by a training strategy using only samples of base audio classes. However, the classifier consisting of prototypes is expanded by a prototype adaptation network with few samples of novel audio classes in incremental sessions. Labeled support samples and unlabeled query samples are used to train the prototype adaptation network and update the classifier, since they are informative for audio classification. Three audio datasets, named NSynth-100, FSC-89 and LS-100 are built by choosing samples from audio corpora of NSynth, FSD-MIX-CLIP and LibriSpeech, respectively. Results show that our method exceeds baseline methods in average accuracy and performance dropping rate. In addition, it is competitive compared to baseline methods in computational complexity and memory requirement.

For two-stage knowledge distillation, the combination with Data Augmentation (DA) is straightforward and effective. Yet, for online Self-knowledge Distillation (SD), DA is not always beneficial because of the absence of a trustworthy teacher model. To address this issue, this paper proposes an SD method named Clean sample guided Self-knowledge Distillation (CleanSD), in which the original clean sample is used as a guide when the model is trained with the augmented samples. The implementation of the CleanSD comes with two DA techniques, namely Mixup (for label-mixing) and Cutout (for label-preserving). Results on CIFAR-100 demonstrate that error rates obtained by the proposed CleanSD are reduced by 2.59%, 1.39%, and 0.47-1.20%, compared to that obtained by the baseline, the vanilla DA techniques, and other peer SD methods, respectively. In addition, the effectiveness and robustness of the CleanSD are verified across multiple DA methods and datasets.

New classes of sounds constantly emerge with a few samples, making it challenging for models to adapt to dynamic acoustic environments. This challenge motivates us to address the new problem of few-shot class-incremental audio classification. This study aims to enable a model to continuously recognize new classes of sounds with a few training samples of new classes while remembering the learned ones. To this end, we propose a method to generate discriminative prototypes and use them to expand the model's classifier for recognizing sounds of new and learned classes. The model is first trained with a random episodic training strategy, and then its backbone is used to generate the prototypes. A dynamic relation projection module refines the prototypes to enhance their discriminability. Results on two datasets (derived from the corpora of Nsynth and FSD-MIX-CLIPS) show that the proposed method exceeds three state-of-the-art methods in average accuracy and performance dropping rate.

Violence detection in videos can help maintain public order, detect crimes, or provide timely assistance. In this paper, we aim to leverage multimodal information to determine whether successive frames contain violence. Specifically, we propose an audiovisual dependency attention (AVD-attention) module modified from the co-attention architecture to fuse visual and audio information, unlike commonly used methods such as the feature concatenation, addition, and score fusion. Because the AVD-attention module’s dependency map contains sufficient fusion information, we argue that it should be applied more sufficiently. A combination pooling method is utilized to convert the dependency map to an attention vector, which can be considered a new feature that includes fusion information or a mask of the attention feature map. Since some information in the input feature might be lost after processing by attention modules, we employ a multimodal low-rank bilinear method that considers all pairwise interactions among two features in each time step to complement the original information for output features of the module. AVD-attention outperformed co-attention in experiments on the XD-Violence dataset. Our system outperforms state-of-the-art systems.

Deep learning based approaches have greatly improved the performance of spoken keyword spotting (KWS). However, KWS of different languages should have their own corresponding modeling units to optimize the performance. In this paper, we propose an end-to-end Mandarin KWS system using Convolutional Recurrent Neural Network with the Connectionist Temporal Classification (CTC) loss function (CRNN-CTC). The tonal syllables are adopted as modeling units. Experiments on AISHELL-2 datasets showed that the proposed approach on the tasks of 13 keywords and 20 keywords can achieve a false rejection rate of 5.35% with 0.26 FA/hour and 6.37% with 0.17 FA/hour, respectively.