191,223 research outputs found
Time-frequency shift-tolerance and counterpropagation network with applications to phoneme recognition
Human speech signals are inherently multi-component non-stationary signals. Recognition schemes for classification of non-stationary signals generally require some kind of temporal alignment to be performed. Examples of techniques used for temporal alignment include hidden Markov models and dynamic time warping. Attempts to incorporate temporal alignment into artificial neural networks have resulted in the construction of time-delay neural networks. The nonstationary nature of speech requires a signal representation that is dependent on time. Time-frequency signal analysis is an extension of conventional time-domain and frequency-domain analysis methods. Researchers have reported on the effectiveness of time-frequency representations to reveal the time-varying nature of speech. In this thesis, a recognition scheme is developed for temporal-spectral alignment of nonstationary signals by performing preprocessing on the time-frequency distributions of the speech phonemes. The resulting representation is independent of any amount of time-frequency shift and is time-frequency shift-tolerant (TFST). The proposed scheme does not require time alignment of the signals and has the additional merit of providing spectral alignment, which may have importance in recognition of speech from different speakers. A modification to the counterpropagation network is proposed that is suitable for phoneme recognition. The modified network maintains the simplicity and competitive mechanism of the counterpropagation network and has additional benefits of fast learning and good modelling accuracy. The temporal-spectral alignment recognition scheme and modified counterpropagation network are applied to the recognition task of speech phonemes. Simulations show that the proposed scheme has potential in the classification of speech phonemes which have not been aligned in time. To facilitate the research, an environment to perform time-frequency signal analysis and recognition using artificial neural networks was developed. The environment provides tools for time-frequency signal analysis and simulations of of the counterpropagation network
Exploiting correlogram structure for robust speech recognition with multiple speech sources
This paper addresses the problem of separating and recognising speech in a monaural acoustic mixture with the presence of competing speech sources. The proposed system treats sound source separation and speech recognition as
tightly coupled processes. In the first stage sound source separation is performed in the correlogram domain. For periodic sounds, the correlogram exhibits symmetric tree-like structures whose stems are located on the delay
that corresponds to multiple pitch periods. These pitch-related structures are exploited in the study to group spectral components at each time frame. Local
pitch estimates are then computed for each spectral group and are used to form simultaneous pitch tracks for temporal integration. These processes segregate a spectral representation of the acoustic mixture into several time-frequency regions such that the energy in each region is likely to have originated from a single periodic sound source. The identified time-frequency regions, together
with the spectral representation, are employed by a `speech fragment decoder' which employs `missing data' techniques with clean speech models to simultaneously search for the acoustic evidence that best matches model sequences. The paper presents evaluations based on artificially mixed simultaneous speech utterances. A coherence-measuring experiment is first reported which quantifies the consistency of the identified fragments with a single source. The system is then evaluated in a speech recognition task and compared to a conventional fragment generation approach. Results show that the proposed system produces more coherent fragments over different conditions,
which results in significantly better recognition accuracy
Improving the robustness of the usual fbe-based asr front-end
All speech recognition systems require some form of signal representation that parametrically models the
temporal evolution of the spectral envelope. Current parameterizations involve, either explicitly or implicitly, a
set of energies from frequency bands which are often distributed in a mel scale. The computation of those filterbank
energies (FBE) always includes smoothing of basic spectral measurements and non-linear amplitude
compression. A variety of linear transformations are typically applied to this time-frequency representation prior
to the Hidden Markov Model (HMM) pattern-matching stage of recognition. In the paper, we will discuss some
robustness issues involved in both the computation of the FBEs and the posterior linear transformations,
presenting alternative techniques that can improve robustness in additive noise conditions. In particular, the root
non-linearity, a voicing-dependent FBE computation technique and a time&frequency filtering (tiffing)
technique will be considered. Recognition results for the Aurora database will be shown to illustrate the potential
application of these alternatives techniques for enhancing the robustness of speech recognition systems.Peer ReviewedPostprint (published version
A spiking neural network for real-time Spanish vowel phonemes recognition
This paper explores neuromorphic approach capabilities applied to real-time speech processing. A spiking
recognition neural network composed of three types of neurons is proposed. These neurons are based on an
integrative and fire model and are capable of recognizing auditory frequency patterns, such as vowel phonemes;
words are recognized as sequences of vowel phonemes. For demonstrating real-time operation, a complete
spiking recognition neural network has been described in VHDL for detecting certain Spanish words, and it has
been tested in a FPGA platform. This is a stand-alone and fully hardware system that allows to embed it in a
mobile system. To stimulate the network, a spiking digital-filter-based cochlea has been implemented in VHDL.
In the implementation, an Address Event Representation (AER) is used for transmitting information between
neurons.Ministerio de Economía y Competitividad TEC2012-37868-C04-02/0
Spectro-Temporal Activity Pattern (STAP) Features for Noise Robust ASR
In this paper, we introduce a new noise robust representation of speech signal obtained by locating points of potential importance in the spectrogram, and parameterizing the activity of time-frequency pattern around those points. These features are referred to as Spectro-Temporal Activity Pattern (STAP) features. The suitability of these features for noise robust speech recognition is examined for a particular parameterization scheme where spectral peaks are chosen as points of potential importance. The activity in the time-frequency patterns around these points are parameterized by measuring the dynamics of the patterns along both time and frequency axes. As the spectral peaks are considered to constitute an important and robust cue for speech recognition, this representation is expected to yield a robust performance. An interesting result of the study is that inspite of using a relatively less amount of information from the speech signal, STAP features are able to achieve a reasonable recognition performance in clean speech, when compared to the state-of-the-art features. In addition, STAP features produce a significantly better performance in high noise conditions. An entropy based combination technique in tandem frame-work to combine STAP features with standard features yields a system which is more robust in all conditions
Deep scattering network for speech emotion recognition
International audienceThis paper introduces scattering transform for speech emotion recognition (SER). Scattering transform generates feature representations which remain stable to deformations and shifting in time and frequency without much loss of information. In speech, the emotion cues are spread across time and localised in frequency. The time and frequency invariance characteristic of scattering coefficients provides a representation robust against emotion irrelevant variations e.g., different speakers, language, gender etc. while preserving the variations caused by emotion cues. Hence, such a representation captures the emotion information more efficiently from speech. We perform experiments to compare scattering coefficients with standard melfrequency cepstral coefficients (MFCCs) over different databases. It is observed that frequency scattering performs better than time-domain scattering and MFCCs. We also investigate layerwise scattering coefficients to analyse the importance of time shift and deformation stable scalogram and modulation spectrum coefficients for SER. We observe that layer-wise coefficients taken independently also perform better than MFCCs
Wavelet methods in speech recognition
In this thesis, novel wavelet techniques are developed to improve parametrization of
speech signals prior to classification. It is shown that non-linear operations carried out
in the wavelet domain improve the performance of a speech classifier and consistently
outperform classical Fourier methods. This is because of the localised nature of the
wavelet, which captures correspondingly well-localised time-frequency features
within the speech signal. Furthermore, by taking advantage of the approximation
ability of wavelets, efficient representation of the non-stationarity inherent in speech
can be achieved in a relatively small number of expansion coefficients. This is an
attractive option when faced with the so-called 'Curse of Dimensionality' problem of
multivariate classifiers such as Linear Discriminant Analysis (LDA) or Artificial
Neural Networks (ANNs). Conventional time-frequency analysis methods such as the
Discrete Fourier Transform either miss irregular signal structures and transients due to
spectral smearing or require a large number of coefficients to represent such
characteristics efficiently. Wavelet theory offers an alternative insight in the
representation of these types of signals.
As an extension to the standard wavelet transform, adaptive libraries of wavelet and
cosine packets are introduced which increase the flexibility of the transform. This
approach is observed to be yet more suitable for the highly variable nature of speech
signals in that it results in a time-frequency sampled grid that is well adapted to
irregularities and transients. They result in a corresponding reduction in the
misclassification rate of the recognition system. However, this is necessarily at the
expense of added computing time.
Finally, a framework based on adaptive time-frequency libraries is developed which
invokes the final classifier to choose the nature of the resolution for a given
classification problem. The classifier then performs dimensionaIity reduction on the
transformed signal by choosing the top few features based on their discriminant power. This approach is compared and contrasted to an existing discriminant wavelet
feature extractor.
The overall conclusions of the thesis are that wavelets and their relatives are capable
of extracting useful features for speech classification problems. The use of adaptive
wavelet transforms provides the flexibility within which powerful feature extractors
can be designed for these types of application
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