A Unified Framework for Detecting Audio Adversarial Examples

Adversarial attacks have been widely recognized as the security vulnerability of deep neural networks, especially in deep automatic speech recognition (ASR) systems. The advanced detection methods against adversarial attacks mainly focus on pre-processing the input audio to alleviate the threat of adversarial noise. Although these methods could detect some simplex adversarial attacks, they fail to handle robust complex attacks especially when the attacker knows the detection details. In this paper, we propose a unified adversarial detection framework for detecting adaptive audio adversarial examples, which combines noise padding with sound reverberation. Specifically, a well-designed adaptive artificial utterances generator is proposed to balance the design complexity, such that the artificial utterances (speech with reverberation) are efficiently determined to reduce the false positive rate and false negative rate of detection results. Moreover, to destroy the continuity of the adversarial noise, we develop a novel multi-noise padding strategy, which implants the Gaussian noises in the silent fragments of the input speech by the voice activity detector. Furthermore, our proposed method can effectively tackle the robust adaptive attacks in an adaptive learning manner. Importantly, the conceived system is easily embedded into any ASR models without requiring additional retraining or modification. The experimental results show that our method consistently outperforms the state-of-the-art audio defense methods, even for the adaptive and robust attacks.