Discusses methods and problems of acoustic signal processing for systems to enable machines to understand spoken communication. Emphasis is on research outside of the ARPA-sponsored SUR (Speech Understanding Research) study. This acoustic level processing includes three steps, not necessarily distinct: (1) preprocessing the original analog signal or its digitized form by basic techniques such as amplitude compression; (2) analysis of the preprocessed signals using fast Fourier transformations, digital filtering, etc.; and (3) parameterizing the results in phoneme-sized chunks by formats, autocorrelation techniques, etc. Problems include (1) environmental noise, (2) transducer limitations, (3) determining an appropriate parameterization technique, and (4) coping with wide phonetic, syntactic, and semantic variability of speech. Choice of the voice coding technique depends on the characteristics of the speech understanding system to be used. Many SUR workers are using linear predictive coding and formant tracking. Progress is being made in segmentation and in use of prosodic features. Uncooperative speakers remain a problem. 37 pp. Ref.
This report is part of the RAND Corporation Report series. The report was a product of the RAND Corporation from 1948 to 1993 that represented the principal publication documenting and transmitting RAND's major research findings and final research.
Our mission to help improve policy and decisionmaking through research and analysis is enabled through our core values of quality and objectivity and our unwavering commitment to the highest level of integrity and ethical behavior. To help ensure our research and analysis are rigorous, objective, and nonpartisan, we subject our research publications to a robust and exacting quality-assurance process; avoid both the appearance and reality of financial and other conflicts of interest through staff training, project screening, and a policy of mandatory disclosure; and pursue transparency in our research engagements through our commitment to the open publication of our research findings and recommendations, disclosure of the source of funding of published research, and policies to ensure intellectual independence. For more information, visit www.rand.org/about/principles.
The RAND Corporation is a nonprofit institution that helps improve policy and decisionmaking through research and analysis. RAND's publications do not necessarily reflect the opinions of its research clients and sponsors.