K. Srinivasa Rao

A novel two stage single channel speech enhancement technique

A two stage novel speech enhancement algorithm is presented in this paper using speech and noise spectral estimators with hybrid a priori SNR combined with perceptual weighting filter. The first stage is designed such that it improves the performance of Minimum Mean Square Error Short-Time Spectral Amplitude (MMSE-STSA) estimator by using hybrid a priori SNR and combining statistical estimators of the spectral magnitude of the speech and noise. A perceptual weighting filter is designed and used as a second stage to improve the intelligibility of the processed speech signal. The performance of proposed scheme is tested and results indicate the performance of the proposed algorithm is better than several other MMSE-STSA algorithms available in literature.

Friction Stir Surfacing Route: Effective Strategy for the Enhancement of Wear Resistance of Titanium Alloy

Titanium alloys are widely used in aerospace applications due to their properties like high strength to weight ratio, good corrosion and creep resistance. Poor wear resistance of these alloys limits their use in tribological applications. Friction surfacing technique is now recognized as an effective solution to surface engineer the light weight high strength alloys to make them suitable for general engineering applications involving wear and corrosion. The present work pertains to a study on wear resistance of surface coating of boron carbide on Ti–6Al–4V alloy using friction surfacing technique. Coating was formed by placing the boron carbide powder into the holes of predetermined depth on the surface and was characterized by metallography, electron probe micro analysis and dry sliding wear testing. The present study revealed that titanium alloy could be friction surfaced with boron carbide powder. The coating exhibited excellent wear resistance, which is attributed to the formation of strong metallurgical bond with the substrate. In the present work an attempt has also been made to compare the wear behaviour of surface composite layer on titanium alloy with that of conventionally used engineering materials such as mild steel and austenitic stainless steel. Wear data clearly revealed that wear resistance of friction stir surfaced composite layer is better than that of mild steel and stainless steel. This study demonstrated that friction stir surfacing is an effective strategy for the enhancement of wear resistance of titanium alloys.

Speech Enhancement Using Cross-Correlation Compensated Multi-Band Wiener Filter Combined with Harmonic Regeneration

The speech signal in general is corrupted by noise and the noise signal does not affect the speech signal uniformly over the entire spectrum. An improved Wiener filtering method is proposed in this paper for reducing background noise from speech signal in colored noise environments. In view of nonlinear variation of human ear sensibility in frequency spectrum, nonlinear multi-band Bark scale frequency spacing approach is used. The cross-correlation between the speech and noise signal is considered in the proposed method to reduce colored noise. To overcome harmonic distortion introduced in enhanced speech, in the proposed method regenerate the suppressed harmonics are regenerated. Objective and subjective tests were carried out to demonstrate improvement in the perceptual quality of speeches by the proposed technique.

Speech enhancement using perceptual Wiener filter combined with unvoiced speech — A new Scheme

A new speech enhancement technique is proposed that reduces musical noise and improves intelligibility of speech. The proposed system has two stages. First stage consists of Wiener filter with self adaptive averaging factor to estimate apriori SNR. To reduce residual musical noise that remains in the enhanced speech, perceptual weighting filter is employed based on simultaneous and temporal masking effects of human auditory system is used in the second stage. An unvoiced speech enhancement algorithm is also integrated in the scheme to improve the intelligibility of speech. Through rigorous objective and subjective evaluations, it is observed that the proposed speech enhancement scheme is capable of reducing noise with little speech distortion in adverse noise environments and the overall performance is superior to several other methods available in literature.

Microstructure and high temperature strength of age hardenable AA2219 aluminium alloy modified by Sc, Mg and Zr additions

Abstract In the present work, it was envisaged to develop thermally stable Al–Cu alloy by modifying its chemistry. AA2219 alloys with different levels of scandium (Sc), magnesium (Mg) and zirconium (Zr) were prepared by melting with inert gas (argon) tungsten arc welding. Sc was added in three levels (0·2, 0·4, 0·8%), Mg one level (0·45%) and Zr one level (0·2%). Optical, scanning electron microscopy (SEM), X-ray diffractometry (XRD) and transmission electron microscopy (TEM) were carried out to study the microstructural details. Long time aging studies and hot tensile tests were used to study the high temperature strength of the alloys. High temperature tensile test was performed on the specimens at 250, 350 and 400°C. Room temperature tensile test was carried out for comparative purpose. Electron probe microscopy analysis (EPMA) was carried out to find out the copper segregation in the alloys. Microstructural studies showed that raising Sc content from 0·2 to 0·8% resulted in significant grain refinement. Grain refinement was much more effective with the addition of 0·2%Zr to AA2219 alloy containing 0·8%Sc and 0·45%Mg. Addition of Sc, Mg and Zr was found to increase in eutectic temperature and decrease in freezing range. Hot tensile results were found to be in agreement with results of hardness data. Among all the compositions, AA2219+0·8%Sc+0·45%Mg+0·2%Zr alloy was found to be the best in terms of its high temperature strength.

Speech enhancement using cross-correlation compensated multi-band Wiener filter combined with constrained perceptual weighting filter

An improved Wiener filtering method for reducing background noise added to speech in colored noise environments like car engine is proposed in this paper. This implementation uses the crosscorrelartion between the speech and noise signals. The noise signal does not affect the speech signal uniformly over the whole spectrum. A nonlinear multi-band Bark scale frequency spacing approach was proposed to reduce colored noise. However, classic short-time noise reduction techniques, including this Wiener filter, introduce some residual noise that remains in the enhanced speech signal. To reduce residual noise the proposed Wiener filter is combined with constrained perceptual weighting filter. Objective and subjective tests demonstrated the proposed technique can improve the perceptual quality of speeches.

A Perceptual Approach to Reduce Musical Noise Using Critical Bands Tonality Coefficients and Masking Thresholds

Traditional noise reduction techniques have the drawback of generating an annoying musical noise. A new scheme for speech enhancement in high noise environment is developed by considering human auditory system masking characteristics. The new scheme considers the masking threshold of both noisy speech and the denoised one, to detect musical noise components. To make them inaudible, they are set under the noise masking threshold. The improved signal is subjected to extensive subjective and objective tests. It is ob-served that the musical noise is appreciably reduced even at very low signal to noise ratios.