Showing papers on "Cepstrum published in 1970"

System for automatic formant analysis of voiced speech.

Abstract: A system for automatically estimating the lowest three formants and the pitch period of voiced speech is presented. The system is based on a digital computation of the cepstrum (defined as the inverse transform of the log magnitude of the z‐transform). The pitch period estimate and smoothed log magnitude are obtained from the cepstrum. Formants are estimated from the smoothed spectral envelope using constraints on formant frequency ranges and relative levels of spectral peaks at the formant frequencies. These constraints allow the detection of cases where two formants are too close together in frequency to be resolved in the initial spectral envelope. In these cases, a new spectral analysis algorithm (the chirp z‐transform algorithm) allows the efficient computation of a narrow‐band spectrum in which the formant resolution is enhanced. Formant and pitch period data obtained by the analysis system are used to control a digital formant synthesizer. Results, in the form of spectrograms, are presented to illu...

Source-Depth Determinations using Spectral, Pseudo-Autocorrelation and Cepstral Analysis

Abstract: Summary Interference between P and pP (or Pn and pPn) in a seismic signal causes the spectrum of the combined wave train to be scalloped with a period equal to the depth-phase delay time τ. Determination of the null frequency interval (Δf= 1/τ), together with a knowledge of the overburden compressional velocity, permits an estimate of the source depth to be made. Scalloping produced by reverberations at the recording station can be reduced by forming the average of a suite of individual station spectra. The spectral bandwidth available for analysis can be broadened by removing instrument response. To determine objectively the periodicities in the average spectrum, the cepstrum and pseudo-autocorrelation are computed. This depth determination method combining spectral, pseudo-autocorrelation, and cepstral analysis is applied successfully to Pn or P data sets for three underground explosions whose depths are known a priori.

Apparatus for reducing multipath distortion of signals utilizing cepstrum technique

Abstract: Distortion of an acoustic signal caused by multipath transmission is minimized by utilizing a cepstrum technique. Signals received at a plurality of microphones are processed to obtain signal representations of their complex cepstrums. The cepstrum signals are then summed. In summing, the portions of the cepstrum signals representative of the undistorted acoustic signal cohere while the portions of the cepstrum signals representative of the multipath transmitted signals do not. Selective clipping of the summed cepstrum signal eliminates the distortion components. Inverse transformation of the clipped summed cepstrum signal yields a replica of the original acoustic signal.