Showing papers on "Cepstrum published in 1976"

Blind deconvolution of spatially invariant image blurs with phase

Abstract: This paper is concerned with the digital estimation of the frequency response of a two-dimensional spatially invariant linear system through which an image has been passed and blurred. For the cases of uniform linear camera motion and an out-of-focus lens system it is shown that the power cepstrum of the image contains sufficient information to identify the blur. Methods for deblurring are presented, including restoration of the density version of the image. The restoration procedure consumes only a modest amount of computation time. Results are demonstrated on images blurred in the camera.

Maximum likelihood pitch estimation

Abstract: A method for estimating the pitch period of voiced speech sounds is developed based on a maximum likelihood (ML) formulation. It is capable of resolution finer than one sampling period and is shown to perform better in the presence of noise than the cepstrum method.

A probabilistic analysis of time delay extraction by the cepstrum in stationary Gaussian noise

Abstract: Often, the cepstrum has been used when estimating the time delay r between elements of a composite signal embedded in noise, n(t) . Here a probabilistic analysis is conducted dealing with the effect of stationary Gaussian noise on the characteristics of such a nonlinear processor. The input noise, n(t) is reflected at the cepstrum's output as: 1) modulation M_{1}(\omega) of sinusoidal information carrier with subsequent reduction in the height of echo peak at \tau ; and 2) generation of background noises \hat{phi}(\omega) and \hat{psi}(\omega) with tendency to obscure that echo peak. The resulting probabilities of these terms are derived. The expected mean and standard deviation of reduction in the peak level at \tau due to noise are analytically described. Similar statistical measures on the background noise are also obtained. The results point out the dependence of the-statistical measures upon the pointwise variation of input signal to noise spectra. Thus the total signal power to total noise power (S/N) alone is an insufficient measure for setting the cepstrum performance, and relative bandwidths of signal and noise are also needed. The detection probability P_{D} of a peak corresponding to \tau is calculated for exponential spectra with equal bandwidths in signal and noise and with echo strength a = 0.4; P_{D} is found to be close to one for an SIN greater than -4 dB; deterioration in detection is found to be rapid with thresholding near an S/N \sim -6 db where P_{D} falls to 0.3.

Use of the cepstrum method for arrival times extraction of overlapping signals due to multipath conditions in shallow water

Abstract: The use of the cepstrum method for signal arrival times extraction of overlapping signals due to multipath conditions in shallow water is considered. The cepstrum method is applied to signal data from a research cruise. The results fall in two parts: (1) the use of a single cepstrum calculation will not clearly identify the different arrival times and (2) the use of several cepstrum calculations gives a consistant pattern of dominant peaks at or near the calculated arrival times. The assumption made in the cepstrum derivation that echoes are replicas of the first arrival is not correct.Subject Classification: [43]30.20; [43]60.30; [43]85.84.

The application of cepstrum technique in power cable fault detection

Abstract: A technique for detecting power cable fault is described. The cable faults are usually characterized by degradation of the dielectric, either by water inclusion or physical cracking and associated voids. Voltage reflected at the fault is modeled as distorted echo. In this technique, a voltage step test signal propagates down the line and reflects energy when a change in impedance occurs. Digitized samples are taken along the return waveform. The power cepstrum of the data is then computed; a simple echo of delay τ produces a ripple in the cepstrum domain of quefrency τ yielding information about the fault location.

Methods for nonlinear spectral distortion of speech signals

Abstract: The spectral distortion of speech signals, without affecting the pitch or the speed of the signal, has met with some difficulty due to the need for pitch extraction. This paper presents a general analysis-synthesis scheme for the arbitrary spectral distortion of speech signals without the need for pitch extraction. Linear predictive warping, cepstral warping, and autocorrelation warping, are given as examples of the general scheme. Applications include the unscrambling of helium speech, spectral compression for the hard of hearing, bit rate reduction in speech compression systems, and efficiency of spectral representation for speech recognition systems.

Advanced Signal Processing.

Abstract: : This final report discusses the technical results from four independent tasks. The effectiveness of the complex cepstrum technique to resolve multipathed acoustic signals was evaluated and compared to autocorrelation techniques. Significant improvements were made in a curvilinear ray theory propagation model, extending accuracy and improving certain algorithms. The maximum entropy spectrum analysis technique was evaluated in terms of estimation accuracy and parameter behavior. A brief description is given of software developed for the OASIS computer system.

Complex Exponential Weighting Applied to Homomorphic Deconvolution

Abstract: Summary The application of exponential weighting to homomorphic deconvolution has been treated extensively by Schafer. This paper considers complex exponential weighting, i.e. multiplication by a" ei6n. At first glance it appears that the phase factor will have no significant effect (just a phase shift) on the complex cepstrum. However, it is shown that a slight modification of the weighting procedure yields a useful technique for the determination of delay times in the cepstrum.

Blind Deconvolution of Spatially invariant image Blurs with Phase

Abstract: Absfruct-This paper is concerned with the digital estimation of the frequency response of a two-dimensional spatially invariant linear system through which an image has been passed and blurred. For the cases of uniform linear camera motion and an out-of-focus lens system it is shown that the power cepstrum of the image contains sufficient information to identify the blur. Methods for deblumng are presented, including restoration of the density version of the image. The restoration procedure consumes only a modest amount of computation time. Results are demonstrated on images blurred in the camera.

Echo reduction in low‐frequency calibration using complex cepstrum

Abstract: The complex cepstrum technique was investigated for possible use in removing echoes caused by early reflections when low‐frequency, peaked‐response transducers are calibrated using transient signals. Synthetic measurement data produced by a J9 projector driven with a damped sinusoidal pulse and a pressure release reflection are shown. Real measurement data from a low‐frequency line array driven by a single‐cycle sinusoid with complex surface and bottom reflections are also shown. In both cases, the echoes were successfully removed using the complex cepstrum technique. Data were digitized directly and stored on digital magnetic tape. Oversampling was reduced by sifting to achieve the correct sampling rate required by the complex cepstrum method. [Supported in part by the Naval Electronic Systems Command.]