Patent
1993-01-25
1995-06-06
MacDonald, Allen R.
G10L 900
Patent
active
054229774
DESCRIPTION:
BRIEF SUMMARY
The invention relates to apparatus and methods for the generation of stabilised images from waveforms. It is particularly applicable to the analysis of non-sinusoidal waveforms which are periodic or quasi-periodic.
Analysis of non-sinusoidal waveforms is particularly applicable to sound waves and to speech recognition systems. Some speech processors begin the analysis of a speech wave by dividing the speech wave into separate frequency channels, either using Fourier Transform methods or a filter bank that mimics that encountered in the human auditory system to a greater or lesser degree. This is done in an attempt to make the speech recognition system noise resistant.
In the Fourier Transform method small segments of the wave are transformed successively from the time domain to the frequency domain, and the components in the resulting spectrum are analysed. This approach is relatively economical, but it has the disadvantage that it destroys the fine grain temporal information in the speech wave before it has been completely analysed.
In the filter bank method the speech wave is divided into channels by filters operating in the time domain, and the result is a set of waveforms each of which carries some portion of the original speech information. The temporal information in each channel is analysed separately and is usually divided into segments and an energy value for each segment determined so that the output of the filter bank is converted into a temporal sequence of energy values. The segment duration is typically in the range 10-40 ms. The integration is insensitive to periodicity in the information in the channel and again fine grain temporal information in the speech wave is destroyed before it has been completely analysed. At the same time with regard to detecting signals in noise, the segment durations referred to above are too short for sufficient integration to take place.
Preferably the temporal integration of a non-sinusoidal waveform is a data-driven process and one which is sensitive and responsive to periodic characteristics of the waveform.
Although the invention may be applied to a variety of waves or mechanical vibrations, the present invention is particularly suited to the analysis of sound waves. The invention is applicable to the analysis of sound waves representing musical notes or speech. In the case of speech the invention is particularly useful for a speech recognition system in which it may be used to assist pitch synchronous temporal integration and to distinguish between periodic signals representing voiced parts of speech and aperiodic signals which may be caused by noise.
The invention may be used to assist pitch synchronous temporal integration generating a stabilised image or representation of a waveform without substantial loss of temporal resolution. The stabilised image of a waveform referred to herein is a representation of the waveform which retains all the important temporal characteristics of the waveform and is achieved through triggered temporal integration of the waveform as described herein.
The present invention seeks to provide apparatus and methods for the generation of a stabilised image from a waveform using a data-driven process and one which is sensitive and responsive to periodic characteristics of the waveform.
The present invention provides a method of generating a stabilised image from a waveform, which method comprises detecting peaks in said waveform, in response to detecting peaks sampling successive time extended segments of said waveform, and forming a summation output by combining first signals representing each successive segment with second signals derived from said summation output formed by previous segments of said waveform, said summation output tending towards a constant when said waveform is constant, whereby said summation output forms a stabilised image of said waveform.
The present invention further provides a method wherein the first and second signals are combined by summing the signals together, the second signals being a reduced sum
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patent: 3087487 (1963-04-01), Clynes
patent: 4802225 (1989-01-01), Patterson
patent: 4969194 (1990-11-01), Ezawa et al.
D. E. Wood: "New Display Format and a Flexible-Time Integrator for Spectral-Analysis Instrumentation"; The Journal of the Acoustical Society of America, vol. 36, No. 4, Apr. 1964; pp. 639-643.
W. Auth et al.: "Dreidimensionale Darstellung von sprachgrundfrequenzsynchron berechneten Sprach-Spektrogrammen-Nachrichtentechnische Zeitschrift N.T.Z., vol. 24, No. 10 Oct. 1971, (Berlin, DE); pp. 502-507.
Holdsworth John W.
Patterson Roy D.
Doerrler Michelle
MacDonald Allen R.
Medical Research Council
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