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This paper describes an online algorithm for enhancing monaural noisy speech. Firstly, a novel phase-corrected low-delay gammatone filterbank is derived for signal subband decomposition and resynthesis; the subband signals are then analyzed frame by frame. Secondly, a novel feature named periodicity degree (PD) is proposed to be used for detecting and estimating the fundamental period (P0) in each frame and for estimating the signal-to-noise ratio (SNR) in each frame-subband signal unit. The PD is calculated in each unit as the multiplication of the normalized autocorrelation and the comb filter ratio, and shown to be robust in various low-SNR conditions. Thirdly, the noise energy level in each signal unit is estimated recursively based on the estimated SNR for units with high PD and based on the noisy signal energy level for units with low PD. Then the a priori SNR is estimated using a decision-directed approach with the estimated noise level. Finally, a revised Wiener gain is calculated, smoothed, and applied to each unit; the processed units are summed across subbands and frames to form the enhanced signal. The P0 detection accuracy of the algorithm was evaluated on two corpora and showed comparable performance on one corpus and better performance on the other corpus when compared to a recently published pitch detection algorithm. The speech enhancement effect of the algorithm was evaluated on one corpus with two objective criteria and showed better performance in one highly non-stationary noise and comparable performance in two other noises when compared to a state-of-the-art statistical-model based algorithm., Comment: 13 pages, 12 figures

Focal mechanisms of earthquakes with 2.5 ≤ M ≤ 4.1 from 1978 to 1990 were analyzed within a 15 km-wide belt of the San Andreas fault (SAF) zone, in the Mojave segment, southern California. Of the 29 events, 41% are strike-slip, 28% oblique--slip, 24% thrust, and 7% are normal fault types. Most of the thrust events are located in the central section of the studied zone, where the fault geometry is relatively simple. In contrast, most of the strike-slip events arc at the intersection between the SAF and the San Jacinto fault. Both stress tensor inverted from slip vectors and strain tensor calculated from earthquake moment tensors produce similar directions of maximum principal compressional axes that arc oriented in the direction between 351° and 5°, which is at an angle of about 60° to the strike of the SAF. These non-SAF type faulting events obviously can not be explained by simple shear motion on the SAF. Instead, they accrued on the structures that were activated in response to the regional N compression at the latitude of the Transverse Ranges. For the thrust events, we interpret that a back thrust (northward thrust) exists beneath the northern side of the San Gabriel Mountains. This back thrust is located at the depth of 8-13 km, within or beneath the Pelona schist. It is apparently associated with aseismic slip and uplifts the San Gabriel Mountains on the northern side.