1,079 research outputs found
Speaker independent isolated word recognition
The work presented in this thesis concerns the recognition of
isolated words using a pattern matching approach. In such a system,
an unknown speech utterance, which is to be identified, is
transformed into a pattern of characteristic features. These
features are then compared with a set of pre-stored reference
patterns that were generated from the vocabulary words. The unknown
word is identified as that vocabulary word for which the reference
pattern gives the best match.
One of the major difficul ties in the pattern comparison process is
that speech patterns, obtained from the same word, exhibit non-linear
temporal fluctuations and thus a high degree of redundancy. The
initial part of this thesis considers various dynamic time warping
techniques used for normalizing the temporal differences between
speech patterns. Redundancy removal methods are also considered, and
their effect on the recognition accuracy is assessed.
Although the use of dynamic time warping algorithms provide
considerable improvement in the accuracy of isolated word recognition
schemes, the performance is ultimately limited by their poor ability
to discriminate between acoustically similar words. Methods for
enhancing the identification rate among acoustically similar words,
by using common pattern features for similar sounding regions, are
investigated.
Pattern matching based, speaker independent systems, can only operate
with a high recognition rate, by using multiple reference patterns
for each of the words included in the vocabulary. These patterns are
obtained from the utterances of a group of speakers. The use of
multiple reference patterns, not only leads to a large increase in
the memory requirements of the recognizer, but also an increase in
the computational load. A recognition system is proposed in this
thesis, which overcomes these difficulties by (i) employing vector
quantization techniques to reduce the storage of reference patterns,
and (ii) eliminating the need for dynamic time warping which reduces
the computational complexity of the system.
Finally, a method of identifying the acoustic structure of an
utterance in terms of voiced, unvoiced, and silence segments by using
fuzzy set theory is proposed. The acoustic structure is then
employed to enhance the recognition accuracy of a conventional
isolated word recognizer
Are words easier to learn from infant- than adult-directed speech? A quantitative corpus-based investigation
We investigate whether infant-directed speech (IDS) could facilitate word
form learning when compared to adult-directed speech (ADS). To study this, we
examine the distribution of word forms at two levels, acoustic and
phonological, using a large database of spontaneous speech in Japanese. At the
acoustic level we show that, as has been documented before for phonemes, the
realizations of words are more variable and less discriminable in IDS than in
ADS. At the phonological level, we find an effect in the opposite direction:
the IDS lexicon contains more distinctive words (such as onomatopoeias) than
the ADS counterpart. Combining the acoustic and phonological metrics together
in a global discriminability score reveals that the bigger separation of
lexical categories in the phonological space does not compensate for the
opposite effect observed at the acoustic level. As a result, IDS word forms are
still globally less discriminable than ADS word forms, even though the effect
is numerically small. We discuss the implication of these findings for the view
that the functional role of IDS is to improve language learnability.Comment: Draf
An acoustic-phonetic approach in automatic Arabic speech recognition
In a large vocabulary speech recognition system the broad phonetic classification
technique is used instead of detailed phonetic analysis to overcome the variability in the
acoustic realisation of utterances. The broad phonetic description of a word is used as a
means of lexical access, where the lexicon is structured into sets of words sharing the
same broad phonetic labelling.
This approach has been applied to a large vocabulary isolated word Arabic speech
recognition system. Statistical studies have been carried out on 10,000 Arabic words
(converted to phonemic form) involving different combinations of broad phonetic
classes. Some particular features of the Arabic language have been exploited. The results
show that vowels represent about 43% of the total number of phonemes. They also show
that about 38% of the words can uniquely be represented at this level by using eight
broad phonetic classes. When introducing detailed vowel identification the percentage of
uniquely specified words rises to 83%. These results suggest that a fully detailed
phonetic analysis of the speech signal is perhaps unnecessary.
In the adopted word recognition model, the consonants are classified into four broad
phonetic classes, while the vowels are described by their phonemic form. A set of 100
words uttered by several speakers has been used to test the performance of the
implemented approach.
In the implemented recognition model, three procedures have been developed, namely
voiced-unvoiced-silence segmentation, vowel detection and identification, and automatic
spectral transition detection between phonemes within a word. The accuracy of both the
V-UV-S and vowel recognition procedures is almost perfect. A broad phonetic
segmentation procedure has been implemented, which exploits information from the
above mentioned three procedures. Simple phonological constraints have been used to
improve the accuracy of the segmentation process. The resultant sequence of labels are
used for lexical access to retrieve the word or a small set of words sharing the same broad
phonetic labelling. For the case of having more than one word-candidates, a verification
procedure is used to choose the most likely one
Word And Speaker Recognition System
In this report, a system which combines user dependent Word Recognition and text dependent speaker recognition is described. Word recognition is the process of converting an audio signal, captured by a microphone, to a word. Speaker Identification is the ability to recognize a person identity base on the specific word he/she uttered. A person's voice contains various parameters that convey information such as gender, emotion, health, attitude and identity. Speaker recognition identifies who is the speaker based on the unique voiceprint from the speech data. Voice Activity Detection (VAD), Spectral Subtraction (SS), Mel-Frequency Cepstrum Coefficient (MFCC), Vector Quantization (VQ), Dynamic Time Warping (DTW) and k-Nearest Neighbour (k-NN) are methods used in word recognition part of the project to implement using MATLAB software. For Speaker Recognition part, Vector Quantization (VQ) is used. The recognition rate for word and speaker recognition system that was successfully implemented is 84.44% for word recognition while for speaker recognition is 54.44%
Representation of Time-Varying Stimuli by a Network Exhibiting Oscillations on a Faster Time Scale
Sensory processing is associated with gamma frequency oscillations (30–80 Hz) in sensory cortices. This raises the question whether gamma oscillations can be directly involved in the representation of time-varying stimuli, including stimuli whose time scale is longer than a gamma cycle. We are interested in the ability of the system to reliably distinguish different stimuli while being robust to stimulus variations such as uniform time-warp. We address this issue with a dynamical model of spiking neurons and study the response to an asymmetric sawtooth input current over a range of shape parameters. These parameters describe how fast the input current rises and falls in time. Our network consists of inhibitory and excitatory populations that are sufficient for generating oscillations in the gamma range. The oscillations period is about one-third of the stimulus duration. Embedded in this network is a subpopulation of excitatory cells that respond to the sawtooth stimulus and a subpopulation of cells that respond to an onset cue. The intrinsic gamma oscillations generate a temporally sparse code for the external stimuli. In this code, an excitatory cell may fire a single spike during a gamma cycle, depending on its tuning properties and on the temporal structure of the specific input; the identity of the stimulus is coded by the list of excitatory cells that fire during each cycle. We quantify the properties of this representation in a series of simulations and show that the sparseness of the code makes it robust to uniform warping of the time scale. We find that resetting of the oscillation phase at stimulus onset is important for a reliable representation of the stimulus and that there is a tradeoff between the resolution of the neural representation of the stimulus and robustness to time-warp.
Author Summary
Sensory processing of time-varying stimuli, such as speech, is associated with high-frequency oscillatory cortical activity, the functional significance of which is still unknown. One possibility is that the oscillations are part of a stimulus-encoding mechanism. Here, we investigate a computational model of such a mechanism, a spiking neuronal network whose intrinsic oscillations interact with external input (waveforms simulating short speech segments in a single acoustic frequency band) to encode stimuli that extend over a time interval longer than the oscillation's period. The network implements a temporally sparse encoding, whose robustness to time warping and neuronal noise we quantify. To our knowledge, this study is the first to demonstrate that a biophysically plausible model of oscillations occurring in the processing of auditory input may generate a representation of signals that span multiple oscillation cycles.National Science Foundation (DMS-0211505); Burroughs Wellcome Fund; U.S. Air Force Office of Scientific Researc
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