5,329 research outputs found
Band-pass filtering of the time sequences of spectral parameters for robust wireless speech recognition
In this paper we address the problem of automatic speech recognition when wireless speech communication systems are involved. In this context, three main sources of distortion should be considered: acoustic environment, speech coding and transmission errors. Whilst the first one has already received a lot of attention, the last two deserve further investigation in our opinion. We have found out that band-pass filtering of the recognition features improves ASR performance when distortions due to these particular communication systems are present. Furthermore, we have evaluated two alternative configurations at different bit error rates (BER) typical of these channels: band-pass filtering the LP-MFCC parameters or a modification of the RASTA-PLP using a sharper low-pass section perform consistently better than LP-MFCC and RASTA-PLP, respectively.Publicad
When the Differences in Frequency Domain are Compensated: Understanding and Defeating Modulated Replay Attacks on Automatic Speech Recognition
Automatic speech recognition (ASR) systems have been widely deployed in
modern smart devices to provide convenient and diverse voice-controlled
services. Since ASR systems are vulnerable to audio replay attacks that can
spoof and mislead ASR systems, a number of defense systems have been proposed
to identify replayed audio signals based on the speakers' unique acoustic
features in the frequency domain. In this paper, we uncover a new type of
replay attack called modulated replay attack, which can bypass the existing
frequency domain based defense systems. The basic idea is to compensate for the
frequency distortion of a given electronic speaker using an inverse filter that
is customized to the speaker's transform characteristics. Our experiments on
real smart devices confirm the modulated replay attacks can successfully escape
the existing detection mechanisms that rely on identifying suspicious features
in the frequency domain. To defeat modulated replay attacks, we design and
implement a countermeasure named DualGuard. We discover and formally prove that
no matter how the replay audio signals could be modulated, the replay attacks
will either leave ringing artifacts in the time domain or cause spectrum
distortion in the frequency domain. Therefore, by jointly checking suspicious
features in both frequency and time domains, DualGuard can successfully detect
various replay attacks including the modulated replay attacks. We implement a
prototype of DualGuard on a popular voice interactive platform, ReSpeaker Core
v2. The experimental results show DualGuard can achieve 98% accuracy on
detecting modulated replay attacks.Comment: 17 pages, 24 figures, In Proceedings of the 2020 ACM SIGSAC
Conference on Computer and Communications Security (CCS' 20
Bio-inspired broad-class phonetic labelling
Recent studies have shown that the correct labeling of phonetic classes may help current Automatic Speech Recognition (ASR) when combined with classical parsing automata based on Hidden Markov Models (HMM).Through the present paper a method for Phonetic Class Labeling (PCL) based on bio-inspired speech processing is described. The methodology is based in the automatic detection of formants and formant trajectories after a careful separation of the vocal and glottal components of speech and in the operation of CF (Characteristic Frequency) neurons in the cochlear nucleus and cortical complex of the human auditory apparatus. Examples of phonetic class labeling are given and the applicability of the method to Speech Processing is discussed
The Cortical Representations of Speech in Reverberant Conditions
Speech intelligibility in adverse situations, such as reverberation and noise, is conserved until the degradations reach certain thresholds. Psychoacoustic studies have described the properties of speech that lead to the conservation of its intelligibility under those circumstances. The neural mechanisms that underlie the robustness of intelligibility in these situations, however, are not yet well understood. Here, the cortical representations of speech in reverberation and speech plus noise in reverberation are studied by measuring the cortical responses of human subjects using magnetoencephalography (MEG) while they listened to continuous speech narratives. It was hypothesized that the neural processing of speech in reverberation and speech plus noise in reverberation would follow a lack of cortical synchronization as function of the degradations. Encoding models show, however, that the neural encoding of speech in reverberation follow a different mechanism than that of speech in noise. On the other hand, in the absence of noise, it is possible to reconstruct with high accuracy the envelope of reverberant speech, thus demonstrating that the reverberant speech is well encoded by the brain
Spread spectrum-based video watermarking algorithms for copyright protection
Merged with duplicate record 10026.1/2263 on 14.03.2017 by CS (TIS)Digital technologies know an unprecedented expansion in the last years. The consumer can
now benefit from hardware and software which was considered state-of-the-art several years
ago. The advantages offered by the digital technologies are major but the same digital
technology opens the door for unlimited piracy. Copying an analogue VCR tape was certainly
possible and relatively easy, in spite of various forms of protection, but due to the analogue
environment, the subsequent copies had an inherent loss in quality. This was a natural way of
limiting the multiple copying of a video material. With digital technology, this barrier
disappears, being possible to make as many copies as desired, without any loss in quality
whatsoever. Digital watermarking is one of the best available tools for fighting this threat.
The aim of the present work was to develop a digital watermarking system compliant with the
recommendations drawn by the EBU, for video broadcast monitoring. Since the watermark
can be inserted in either spatial domain or transform domain, this aspect was investigated and
led to the conclusion that wavelet transform is one of the best solutions available. Since
watermarking is not an easy task, especially considering the robustness under various attacks
several techniques were employed in order to increase the capacity/robustness of the system:
spread-spectrum and modulation techniques to cast the watermark, powerful error correction
to protect the mark, human visual models to insert a robust mark and to ensure its invisibility.
The combination of these methods led to a major improvement, but yet the system wasn't
robust to several important geometrical attacks. In order to achieve this last milestone, the
system uses two distinct watermarks: a spatial domain reference watermark and the main
watermark embedded in the wavelet domain. By using this reference watermark and techniques
specific to image registration, the system is able to determine the parameters of the attack and
revert it. Once the attack was reverted, the main watermark is recovered. The final result is a
high capacity, blind DWr-based video watermarking system, robust to a wide range of attacks.BBC Research & Developmen
- âŠ