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Improved hidden Markov model speech recognition using radial basis function networks

Published in:
Advances in Neural Information Processing Systems, Denver, CO, 2-5 December 1991.

Summary

A high performance speaker-independent isolated-word hybrid speech recognizer was developed which combines Hidden Markov Models (HMMs) and Radial Basis Function (RBF) neural networks. In recognition experiments using a speaker-independent E-set database, the hybrid recognizer had an error rate of 11.5% compared to 15.7% for the robust unimodal Gaussian HMM recognizer upon which the hybrid system was based. These results and additional experiments demonstrate that RBF networks can be successfully incorporated in hybrid recognizers and suggest that they may be capable of good performance with fewer parameters than required by Gaussian mixture classifiers. A global parameter optimization method designed to minimize the overall word error rather than the frame recognition error failed to reduce the error rate.
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Summary

A high performance speaker-independent isolated-word hybrid speech recognizer was developed which combines Hidden Markov Models (HMMs) and Radial Basis Function (RBF) neural networks. In recognition experiments using a speaker-independent E-set database, the hybrid recognizer had an error rate of 11.5% compared to 15.7% for the robust unimodal Gaussian HMM recognizer...

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A new application of adaptive noise cancellation

Published in:
IEEE Trans. Acoust., Speech, Sig Process., Vol. ASSP-34, No. 1, February 1986, pp. 21-7.

Summary

A new application of Widrow's adaptive noise cancellation (ANC) is presented in this paper. Specifically, the method is applied to the case where an acoustic barrier exists between the primary and reference microphones. By updating the coefficients of the noise estimation filter only during silence, it is shown that ANC can provide substantial noise reduction with little speech distortion even when the acoustic barrier provides only moderate attenuation of acoustic signals. The use of the modified ANC method is evaluated using an oxygen facemask worn by fighter aircraft pilots. Experiments demonstrate that if a noise field is created using a single source, 11 dB signal-to-noise ratio improvements can be achieved by attaching a reference microphone to the exterior of the facemask. The length of the ANC filter required for this particular environment is only 50 points.
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Summary

A new application of Widrow's adaptive noise cancellation (ANC) is presented in this paper. Specifically, the method is applied to the case where an acoustic barrier exists between the primary and reference microphones. By updating the coefficients of the noise estimation filter only during silence, it is shown that ANC...

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Adaptive noise cancellation in a fighter cockpit environment

Published in:
ICASSP'84, IEEE Int. Conf. on Acoustics, Speech and Signal Processing, 19-21 March 1984.

Summary

In this paper we discuss some preliminary results on using Widrow's Adaptive Noise Cancelling (ANC) algorithm to reduce the background noise present in a fighter pilot's speech. With a dominant noise source present and with the pilot wearing an oxygen facemask, we demonstrate that good (>10 dB) cancellation of the additive noise and little speech distortion can be achieved by having the reference microphone attached to the outside of the facemask and by updating the filter coefficients only during silence intervals.
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Summary

In this paper we discuss some preliminary results on using Widrow's Adaptive Noise Cancelling (ANC) algorithm to reduce the background noise present in a fighter pilot's speech. With a dominant noise source present and with the pilot wearing an oxygen facemask, we demonstrate that good (>10 dB) cancellation of the...

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The effects of microphones and facemasks on LPC vocoder performance

Author:
Published in:
Proc. of IEEE Int. Conf. on Acoustics, Speech & Signal Processing, 30 March - 1 April 1981.

Summary

The effects of oxygen facemasks and noise cancelling microphones on LPC vocoder performance were analyzed and evaluated. Likely sources of potential vocoder performance degradation included the non-ideal frequency response characteristics of the microphone and the possible presence of additional resonances in the speech waveform due to the addition of the facemask cavity. Examination of vowel spectra revealed that spurious resonances do not occur in the vocoder frequency band for speech generated using the facemask and microphone. Also observed was a vowel-dependent reduction in the bandwidths of the upper formants, a result which can be predicted from acoustic theory. Finally, it is shown that the low frequency emphasis associated with small enclosures is not relevant when using a pressure gradient (noise cancelling) microphone. Diagnostic Rhyme Tests involving three subjects indicated that the presence of the oxygen facemask and noise cancelling microphone did not result in a significant increase in the LPC vocoder processing loss.
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Summary

The effects of oxygen facemasks and noise cancelling microphones on LPC vocoder performance were analyzed and evaluated. Likely sources of potential vocoder performance degradation included the non-ideal frequency response characteristics of the microphone and the possible presence of additional resonances in the speech waveform due to the addition of the...

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A split band adaptive predictive coding (SBAPC) speech system

Published in:
IEEE Int. Conf. on Acoustics, Speech, & Signal Processing, 9-11 April 1980.

Summary

As developed by Atal and Schroeder [1], conventional Adaptive Predictive Coding (APC) of speech employs both vocal tract and pitch prediction to achieve a low energy, spectrally flattened residual. Errors in the pitch predictor can result in clipping errors which can propagate in the system for relatively long periods of time and degrade the quality of the synthesized speech. Makhoul and Berouti [2] have developed a high quality 16 kbps APC system which eliminates the pitch predictor by using a multi-level variable rate quantizer. In order to achieve comparable quality at even lower data rates, a split band APC (SBAPC) structure is proposed which employs the multi-level quantizer on the low frequency portion of the residual and a 1-bit quantizer on the high frequency portion of the residual.
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Summary

As developed by Atal and Schroeder [1], conventional Adaptive Predictive Coding (APC) of speech employs both vocal tract and pitch prediction to achieve a low energy, spectrally flattened residual. Errors in the pitch predictor can result in clipping errors which can propagate in the system for relatively long periods of...

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