This paper describes a method to extract fundamental frequencies of speech signals for use in speech analysis-synthesis systems. The method is based on peak-picking of squared and filtered speech waveforms. The following two filter characteristics are tried : (1) sin_2(ωt/2)/(ωt/2). (2) jωa/(jω+a)_2. Both filters are used in cascade with a low pass filter the unit response curve of which is the same as the Hamming window function. A new peak-picking method and a new period decision logic are also developed. In order to evaluate this method, gross pitch errors, unvoiced-to-voiced errors and voiced-to-unvoiced errors are calculated for the two filter characteristics. A_nA/B preference test is also conducted on speech samples which are LPC analyzed and synthesized. A female voice, a male voice and a telephone-band-limited male voice are used as the test samples. It is concluded that the method proposed here has higher preference score than the cepstral method, and that in the case of the telephone-band-limited voice, the second filter is preferable to the first one.
A unified theory on the scattering from weakly inhomogeneous dispersive media at high volumetric concentration of dispersed materials is introduced in this presentation. This problem which seems rather simple is certainly important in the understanding of the acoustic structure of biological tissue for recent approaches to tissue characterization with ultrasound. This paper describes the derivation of scattering intensity of acoustical waves from the weakly inhomogeneous dispersive medium under the conditions of long wave incidence and far-field observation from the viewpoint of statistical continuum theory. 1) Effective physical constants of the dispersive medium, such as adiabatic compressibility ; κ and spatial density ; γ are strictly defined by assuming statistical continuity of the space, and the general formula of wave equation for weakly inhomogeneous medium is derived. 2) Secondary wave from the spatial fluctuations of acoustical constants around their effective values is derived for primal incidence of plane wave by using the method of small perturbation, which is called Born Approximation. 3) The 2-point correlation function of random aggregates of monodisperse spheres is proposed as a modification of Debye's formulation. 4) Differential scattering cross section per unit sample volume is calculated for the evaluation of the averaged scattering intensity.
The vibration of the piano string which is struck by an elastic hammer, is studied by equivalent electric circuit models of impedance analogy and mobility analogy. When the elasticity of the piano string may be neglected and only the tension is considered, the stiff string can be regarded as an electrical transmission line. The hammer can be expressed as the inductance and the capacitance. In order to get the vibration of the struck string, an analog simulator, based on the model, is designed and used. Waveforms, contact time and maximum struck force are calculated by the simulator. The reason of the appearance of the even harmonics series in the high frequency region, and the method of the adjustment are also shown clearly by means of the simulator. The vertical tension waveforms are determined from the synthesis of shifting the phase of two struck string force waveforms. The velocity waveforms are also determined from the synthesis for the two vertical tension waveforms. The characteristics of these waveforms are shown and compared with measured waveforms. The struck string forces, which reduce the vertical tensions, are calculated from the equivalent circuits. In every case, their waves become very similar to the damped half sinusoidal waves. At last, considerations on energy transmission from the hammer to the string are made. Specially, the efficiency at low frequency region is discussed.