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Mixed-phase deconvolution of speech based on a sine-wave model

Published in:
Proc. IEEE Int. Conf. on Acoustics, Speech and Signal Processing, ICASSP, Vol. 2, 6-9 April 1987, pp. 649-652.

Summary

This paper describes a new method of deconvolving the vocal cord excitation and vocal tract system response. The technique relies on a sine-wave representation of the speech waveform and forms the basis of an analysis-synthesis method which yields synthetic speech essentially indistinguishable from the original. Unlike an earlier sinusoidal analysis-synthesis technique that used a minimum-phase system estimate, the approach in this paper generates a "mixed-phase" system estimate and thus an improved decomposition of excitation and system components. Since a mixed-phase system estimate is removed from the speech waveform, the resulting excitation residual is less dispersed than the previous sinusoidal-based excitation estimate of the more commonly used linear prediction residual. A method of time-varying linear filtering is given as an alternative to sinusoidal reconstruction, similar to conventional time-domain synthesis used in certain vocoders, but without the requirement of pitch and voicing decisions. Finally, speech modification with a mixed-phase system estimate is shown to be capable of more closely preserving waveform shape in time-scale and pitch transformations than the earlier approach.
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Summary

This paper describes a new method of deconvolving the vocal cord excitation and vocal tract system response. The technique relies on a sine-wave representation of the speech waveform and forms the basis of an analysis-synthesis method which yields synthetic speech essentially indistinguishable from the original. Unlike an earlier sinusoidal analysis-synthesis...

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Speech transformations based on a sinusoidal representation

Published in:
IEEE Trans. Acoust. Speech Signal Process., Vol. ASSP-34, No. 6, December 1986, pp. 1449-1464.

Summary

In this paper a new speech analysis/synthesis technique is presented which provides the basis for a general class of speech transformations including time-scale modification, frequency scaling, and pitch modification. These modifications can be performed with a time-varying change, permitting continuous adjustment of a speaker's fundamental frequency rate of articulation. The method is based on a sinusoidal representation of the speech production mechanism which has been shown to produce synthetic speech that preserves the waveform shape and is perceptually indistinguishable from the original. Although the analysis/synthesis system was originally designed for single speaker signals, it is also capable ot recovering and modifying non-speech signals such as music, multiple speakers, marine biologic sounds, and speakers in the presence of interferences such as noise and musical backgrounds.
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Summary

In this paper a new speech analysis/synthesis technique is presented which provides the basis for a general class of speech transformations including time-scale modification, frequency scaling, and pitch modification. These modifications can be performed with a time-varying change, permitting continuous adjustment of a speaker's fundamental frequency rate of articulation. The...

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Speech analysis/synthesis based on a sinusoidal representation

Published in:
IEEE Trans. Acoust. Speech Signal Process., Vol. ASSP-34, No. 4, August 1986, pp. 744-754.

Summary

A sinusoidal model for the speech waveform is used to develop a new analysis/synthesis technique that is characterized by the amplitudes, frequencies, and phases of the component sine waves. These parameters are estimated from the short-time Fourier transform using a simple peak-picking algorithm. Rapid changes in the highly resolved spectral components are tracked using the concept of "birth" and "death" of the underlying sine waves. For a given frequency track a cubic function is used to unwrap and interpolate the phase such that the phase track is maximally smooth. This phase function is applied to a sine-wave generator, which is amplitude modulated and added to the other sine waves to give the final speech output. The resulting synthetic waveform preserves the general waveform shape and is essentially perceptually indistinguishable from the original speech. Furthermore, in the presence of noise the perceptual characteristics of the speech as well as the noise are maintained. In addition, it was found that the representation was sufficiently general that high-quality reproduction was obtained for a larger class of inputs including: two overpallping, superposed speech waveforms; music waveforms; speech in musical backgrounds; and certain marine biologic sounds. Finally, the analysis/synthesis system forms the basis for new approaches to the problems of speech transformations including time-scale and pitch-scale modification, and midrate speech coding.
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Summary

A sinusoidal model for the speech waveform is used to develop a new analysis/synthesis technique that is characterized by the amplitudes, frequencies, and phases of the component sine waves. These parameters are estimated from the short-time Fourier transform using a simple peak-picking algorithm. Rapid changes in the highly resolved spectral...

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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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Interferometer design for elevation angle estimation

Published in:
IEEE Trans. Aerosp. Electron. Syst., Vol. AES-13, No. 5, September 1977, pp. 486-503.

Summary

Radars that are developed for the purpose of monitoring aircraft landings in the terminal air traffic control system can be designed to exploit the relatively high signal-to-noise ratio that characterizes the power budgets calculated for such a link. An interferometer using a pair of low gain antennas can be used to obtain passive coverage over a target azimuth and elevation sector. A large baseline can be used to obtain the desired elevation angle estimation accuracy. In this paper an optimal tradeoff between the width of the subarray aperture and the width of the interferometer baseline is performed that achieves a specified elevation angle estimation error while minimizing the overall height of the interferometer configuration. The algorithm searches through the class of antenna patterns that can be synthesized from so-called finite impulse response, linear phase digital filters. For the specific problem of designing an elevation sensor for monitoring landing aircraft on final approach, the elevation angle can be estimated with no more than 1-mrad rms error when the aircraft is within 60 azimuth, 2.5 to 40 elevation, using two 7-wavelength subarray antennas spaced 8 wave-lengths apart. The design of a separate sensor for resolving the interferometer ambiguities is formulated as a hypothesis testing problem and solved using statistical decision theory. A bound on the probability of an ambiguity error is derived that accounts for the effects of ground reflection multipath and receiver noise.
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Summary

Radars that are developed for the purpose of monitoring aircraft landings in the terminal air traffic control system can be designed to exploit the relatively high signal-to-noise ratio that characterizes the power budgets calculated for such a link. An interferometer using a pair of low gain antennas can be used...

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PALM - a system for precise aircraft location

Published in:
J. of the Institute of Navigation, Vol. 23, No. 3, Fall 1976, pp. 257-261.

Summary

The Precision Altitude and Landing Monitor (PALM) is intended to provide accurate stand-alone three-dimensional position data for aircraft equipped with standard beacon transponders using ground equipment designed for low life cycle cost. The PALM program, to the present time, has focused on an experimental evaluation of the accuracy of elevation measurements. The results of these measurements have successfully validated the theoretical prediction of a 1-mrad (0.06 degree) elevation accuracy at low elevation angles. The key features in the PALM design include (1) No new avionics required, i.e., it uses standard aircraft transponder. IFPALM is used as the data base for certain ground-to-air messages, a standard VHF or DABS data link could be employed. (2) High accuracy position data, i.e., a 1-mrad rms error in elevation and in azimuth at low elevation angles. (3) Broad airspace coverage, e.g., 40 degrees in elevation, 120 degrees in azimuth (expandable to 360 degrees), and several tens of miles in range. (4) Low life cycle equipment cost, i.e., it incorporates a fixed passive receiving antenna array and a minicomputer to perform the signal processing necessary for interference rejection.
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Summary

The Precision Altitude and Landing Monitor (PALM) is intended to provide accurate stand-alone three-dimensional position data for aircraft equipped with standard beacon transponders using ground equipment designed for low life cycle cost. The PALM program, to the present time, has focused on an experimental evaluation of the accuracy of elevation...

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Optimum elevation angle estimation in the presence of ground reflection multipath

Published in:
MIT Lincoln Laboratory Report TN-1976-11

Summary

An optimal trade-off between the width of the subarray aperture and the width of the interferometer base line is performed that achieves a specified elevation angle estimation error while minimizing the overall height of the interferometer configuration. Statistical decision theory is used to analyze and design a separate sensor for resolving the interferometer ambiguities. For coverage over 2.5 to 40 in elevation and +/-60 in azimuth, two 7-wavelength subarrays separated by 8 wavelengths are sufficient for 1-mrad elevation-angle errors. A 4-element nonuniformly spaced array of dipole antennas mounted on tri-plane reflectors renders the probability of an ambiguity error less than 0.004.
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Summary

An optimal trade-off between the width of the subarray aperture and the width of the interferometer base line is performed that achieves a specified elevation angle estimation error while minimizing the overall height of the interferometer configuration. Statistical decision theory is used to analyze and design a separate sensor for...

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Experimental validation of PALM - a system for precise aircraft location

Summary

A ground based system to precisely locate aircraft in three dimensions based on transponder replies has been designed. Field tests have been conducted to validate the design of the elevation performance. This document reports on the principle of operation, experimental hardware and field test of the Precision Altitude and Landing Monitor (PALM). The key features incorporated in the PALM design include: (a) no new avionics required, i.e., uses standard aircraft transponder; (b) high accuracy position data, i.e., a 1-mrad (0.06 degree) rms error in elevation and in azimuth; (c) broad airspace coverage, e.g., 40 degrees in elevation, 120 degrees in azimuth (expandable to 360 degrees) and several 10s of miles in range; and (d) low life cycle equipment cost. The high accuracy in the difficult airport multipath environment is a direct result of (a) newly developed antenna synthesis procedure, (b) the development of adaptive multipath suppression techniques, and (c) the use of digital signal processing. The program, to date, has focused on an experimental evaluation of the elevation performance. The electronics required for the tests have been built into a self-powered van to facilitate experiments at remote airports. The actual flight test data demonstrated experimental errors on the order of 1 mrad; moreover, as predicted by theory, the resulting errors were essentially independent of elevation angle. Potential applications for the PALM position data include parallel approach monitoring, independent altitude monitoring, and/or performance assurance monitoring of landing guidance systems.
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Summary

A ground based system to precisely locate aircraft in three dimensions based on transponder replies has been designed. Field tests have been conducted to validate the design of the elevation performance. This document reports on the principle of operation, experimental hardware and field test of the Precision Altitude and Landing...

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Maximum-likelihood detection of unresolved radar targets and multipath

Published in:
IEEE Trans. Aerosp. Electron. Syst., Vol. AES-10, No. 6, November 1974, pp. 821-9.

Summary

Interference in the form of multipath or uncooperative targets can seriously degrade the angle-of-arrival estimation accuracy of mutiple beam processors. In this paper, the generalized likelihood ratio test is used to derive a test to detect the presence of interference for multiple beam processors. The detector performance is then analyzed in detail with respect to its dependence on signal-to-noise ratio (SNR), signal-to-interference ration (SIR), and on the relative phase between the target and interfering signals. It is shown that good detection performance can be obtained unless the phase difference between the target and interference signals is either in or out of phase.
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Summary

Interference in the form of multipath or uncooperative targets can seriously degrade the angle-of-arrival estimation accuracy of mutiple beam processors. In this paper, the generalized likelihood ratio test is used to derive a test to detect the presence of interference for multiple beam processors. The detector performance is then analyzed...

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Simulation of the DABS sensor for evaluating reply processor performance

Author:
Published in:
MIT Lincoln Laboratory Report ATC-28

Summary

This report describes the elements of a simulations program that was designed to perform a realistic evaluation of a variety of reply processing techniques, antenna design parameters and receiver characteristics for a DABS sensor. The reply processing techniques are limited to the generation of information bit and monopulse off-boresight azimuth estimates for DABS downlink messages. The report describes the detailed characteristics of two elements of the simulation program; the data generator and reply processor, and the high degree of versatility incorporated within these elements to allow for a great many performance tradeoff studies.
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Summary

This report describes the elements of a simulations program that was designed to perform a realistic evaluation of a variety of reply processing techniques, antenna design parameters and receiver characteristics for a DABS sensor. The reply processing techniques are limited to the generation of information bit and monopulse off-boresight azimuth...

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