Showing papers by "Patrick J. Loughlin published in 1991"
14 Apr 1991
TL;DR: Two properties are presented that constrain the cross-terms of Cohen-class time-frequency representations (TFRs) to appear only at signal frequencies, and only when the signal is nonzero, i.e. the TFR is zero everywhere the signal or its spectrum is zero.
Abstract: Two properties are presented that constrain the cross-terms of Cohen-class time-frequency representations (TFRs) to appear only at signal frequencies, and only when the signal is nonzero. These properties thus guarantee strong finite support, i.e. the TFR is zero everywhere the signal or its spectrum is zero. When combined with cross-term attenuation, one can obtain TFRs with spectrogram-like interference suppression, but without the inherent time-frequency resolution tradeoff of the spectrogram. >
16 citations
01 Dec 1991
TL;DR: It is shown how quadratic time-frequency representations are a generalization of the spectrogram and the results for time- Frequency analysis and display of chirps and speech are reviewed and the resolution advantages over linear filtering are demonstrated.
Abstract: In this paper, we show how quadratic time-frequency representations are a generalization of the spectrogram and we review our results for time-frequency analysis and display of chirps and speech. We then show comparative performance on phase-shifted keyed communication signals. The concept of quadratic filtering is then introduced and linked to Teager's energy detector and the resolution advantages over linear filtering are demonstrated.© (1991) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.
11 citations
14 Apr 1991
TL;DR: It is shown that interference-free representations of speech with a higher simultaneous resolution in time and frequency than the spectrogram are possible, and that these new representations may be applicable to the better analysis and understanding of speech.
Abstract: The assumption of quasi-stationarity in the analysis of speech is questioned from the standpoint of the best resolution of global periodicity and vocal tract formant frequency locations. The generalized class of time-frequency representations is discussed from the standpoint of speech analysis and is integrated with a description of the spectrogram. The spectrogram is known to have minimal interference artifacts, and the truly nonstationary cone-kernel time-frequency representation (CK-TFR) is shown to be similarly free of interference. The CK-TFR is observed to give higher resolution of the time point of glottal closure, and the clarity of some formant frequencies, especially for a nasal consonant, is shown to be better than the spectrogram. It is shown that interference-free representations of speech with a higher simultaneous resolution in time and frequency than the spectrogram are possible, and that these new representations may be applicable to the better analysis and understanding of speech. >
10 citations
04 Nov 1991
TL;DR: In this article, the use of the cone kernel time-frequency representation (CK-TFR) for shift-keyed signal identification is introduced, which can distinguish between phase shifts of 180, +90, and -90 degrees.
Abstract: The use of the cone kernel time-frequency representation (CK-TFR) for shift-keyed signal identification is introduced. In electronic warfare surveillance systems, the identification of phase shifts in a signal is an important topic due to the prevalent use of phase-shift keyed signalling schemes. Examples of TFR patterns for shift-keyed signals are presented. It is observed that, in addition to providing baud rate information about the signal, the CK-TFR clearly distinguishes between phase shifts of 180, +90, and -90 degrees . A 'spectral peak splitting' effect is observed in the CK-TFR coincident with phase shifts in a signal. The mathematical foundation for the spectral peak splitting is explored. >
3 citations
09 May 1991
TL;DR: The authors discuss a complementary processing methodology, the cone kernel time-frequency representation, that may provide improved performance for target classification, especially in low signal-to-noise (SNR) environments, where the cone Kernel processing outperforms the matched filter in Doppler estimation.
Abstract: Range-Doppler processing is the primary tool in active sonar and radar imaging. The matched-filter is the optimal detector in sonar and radar, but has drawbacks in time and frequency resolution which may hinder its performance as a classifier. The authors discuss a complementary processing methodology, the cone kernel time-frequency representation, that, although slightly suboptimal in a detection sense, yields simultaneously good resolution in time and frequency (range and Doppler). This processing may provide improved performance for target classification, especially in low signal-to-noise (SNR) environments, where the cone kernel processing outperforms the matched filter in Doppler estimation. >
3 citations
09 May 1991
TL;DR: It is concluded that frequency transforms are needed for the simple case of speaker-independent vowel recognition.
Abstract: The design of preprocessors, or front-ends, for a speech recognition system is considered to be critical to the overall performance of the system. A design methodology, which is inspired by and, in some ways, formulated from the theory of time-frequency analysis, is presented. Examples of specific desirable properties for preprocessors are presented, and preliminary results supporting the need for a frequency transform are summarized. The authors propose eight properties for speech preprocessors. The last property, that of frequency analysis, was experimentally confirmed for single short segments of speaker-independent vowels. It is concluded that frequency transforms are needed for the simple case of speaker-independent vowel recognition. >
1 citations