Hybrid Time-frequency Domain Research Articles

Earthquake Response of Concrete Gravity Dams Including Base Sliding

The stability of a concrete gravity dam against sliding along the interface between the dam base and the foundation rock must be assured in a seismic safety evaluation. The hybrid frequency–time domain procedure is used to compute the earthquake response of gravity dams, including base sliding. The procedure accounts for the nonlinear base sliding of the dam and the frequency-dependent response of the impounded water and the flexible foundation rock. A parameter study of typical gravity dams shows how the earthquake-induced sliding is affected by the characteristics of the ground motion and dam system. Based on the results of the study, it is necessary to include the effects of dam–foundation rock interaction to obtain realistic estimates of the base sliding displacement for a dam. The sliding displacement is sensitive to the value of the coefficient of friction for the interface zone, especially for moderate to tall dams. Water compressibility also affects the base sliding displacement. Although a dam re...

Acoustic-to-articulatory mapping of fricatives

This research considers the acoustic-to-articulatory mapping of fricative speech. By incorporating additional knowledge about fricative production, perception, and dynamics into the mapping scheme, improved performance may be achieved over standard acoustic-to-articulatory mapping techniques. A hybrid time-frequency domain articulatory synthesizer and numerical optimization techniques are applied to steady-state, unvoiced fricatives. The work differs from the fricative inverse mapping experiments of Sorokin [V. Sorokin, Speech Commun. 14, 249–262 (1994)] and Shirai [K. Shirai and S. Masaki, Speech Commun. 2, 111–114 (1983)] in that a fricative-specific linked codebook is used to initialize optimization and amplitude sensitive distance measures are used. The fricative codebook produces starting configurations for numerical optimization based on their spectral characteristics and their ability to match frication source characteristics for a given lung pressure and glottal configuration. The use of amplitude sensitive spectral distance measures is necessary to account for the interaction between the tract and the flow-dependent frication source. Examples of acoustic-to-articulatory mapping are given that compare fricative articulatory models and fricative spectral distance measures for the inverse mapping scheme. Acoustic-to-articulatory performance is evaluated in terms of spectral distance and clustering ability. [Work supported by the AFOSR.]

A hybrid time-frequency domain articulatory speech synthesizer

High quality speech at low bit rates (e.g., 2400 bits/s) is one of the important objectives of current speech research. As part of long range activity on this problem, we have developed an efficient computer program that will serve as a tool for investigating whether articulatory speech synthesis may achieve this low bit rate. At a sampling frequency of 8 kHz, the most comprehensive version of the program, including nasality and frication, runs at about twice real time on a Cray-1 computer.