Minimum Mean-square Error Short-time Spectral Amplitude Research Articles

RDN-NET: A Deep Learning Framework for Asthma Prediction and Classification Using Recurrent Deep Neural Network

Asthma is the one of the crucial types of disease, which causes the huge deaths of all age groups around the world. So, early detection and prevention of asthma disease can save numerous lives and are also helpful to the medical field. But the conventional machine learning methods have failed to detect the asthma from the speech signals and resulted in low accuracy. Thus, this paper presented the advanced deep learning-based asthma prediction and classification using recurrent deep neural network (RDN-Net). Initially, speech signals are preprocessed by using minimum mean-square-error short-time spectral amplitude (MMSE-STSA) method, which is used to remove the noises and enhances the speech properties. Then, improved Ripplet-II Transform (IR2T) is used to extract disease-dependent and disease-specific features. Then, modified gray wolf optimization (MGWO)-based bio-optimization approach is used to select the optimal features by hunting process. Finally, RDN-Net is used to predict the asthma disease present from speech signal and classifies the type as either wheeze, crackle or normal. The simulations are carried out on real-time COSWARA dataset and the proposed method resulted in better performance for all metrics as compared to the state-of-the-art approaches.

Spectral distortion level resulting in a just-noticeable difference between an a priori signal-to-noise ratio estimate and its instantaneous case.

Minimum mean-square error (MMSE) approaches to speech enhancement are widely used in the literature. The quality of enhanced speech produced by an MMSE approach is directly impacted by the accuracy of the employed a priori signal-to-noise ratio (SNR) estimator. In this paper, the a priori SNR estimate spectral distortion (SD) level that results in a just-noticeable difference (JND) in the perceived quality of MMSE approach enhanced speech is found. The JND SD level is indicative of the accuracy that an a priori SNR estimator must exceed to have no impact on the perceived quality of MMSE approach enhanced speech. To measure the JND SD level, listening tests are conducted across five SNR levels, five noise sources, and two MMSE approaches [the MMSE short-time spectral amplitude (MMSE-STSA) estimator and the Wiener filter]. A statistical analysis of the results indicates that the JND SD level increases with the SNR level, is higher for the MMSE-STSA estimator, and is not impacted by the type of background noise. Following the literature, a significant improvement in a priori SNR estimation accuracy is required to reach the JND SD level.

Deep learning for minimum mean-square error approaches to speech enhancement

Recently, the focus of speech enhancement research has shifted from minimum mean-square error (MMSE) approaches, like the MMSE short-time spectral amplitude (MMSE-STSA) estimator, to state-of-the-art masking- and mapping-based deep learning approaches. We aim to bridge the gap between these two differing speech enhancement approaches. Deep learning methods for MMSE approaches are investigated in this work, with the objective of producing intelligible enhanced speech at a high quality. Since the speech enhancement performance of an MMSE approach improves with the accuracy of the used a priori signal-to-noise ratio (SNR) estimator, a residual long short-term memory (ResLSTM) network is utilised here to accurately estimate the a priori SNR. MMSE approaches utilising the ResLSTM a priori SNR estimator are evaluated using subjective and objective measures of speech quality and intelligibility. The tested conditions include real-world non-stationary and coloured noise sources at multiple SNR levels. MMSE approaches utilising the proposed a priori SNR estimator are able to achieve higher enhanced speech quality and intelligibility scores than recent masking- and mapping-based deep learning approaches. The results presented in this work show that the performance of an MMSE approach to speech enhancement significantly increases when utilising deep learning.Availability: The proposed a priori SNR estimator is available at: https://github.com/anicolson/DeepXi.

Spectral Restoration Based Speech Enhancement for Robust Speaker Identification

Spectral restoration based speech enhancement algorithms are used to enhance quality of noise masked speech for robust speaker identification. In presence of background noise, the performance of speaker identification systems can be severely deteriorated. The present study employed and evaluated the Minimum Mean-SquareError Short-Time Spectral Amplitude Estimators with modified a priori SNR estimate prior to speaker identification to improve performance of the speaker identification systems in presence of background noise. For speaker identification, Mel Frequency Cepstral coefficient and Vector Quantization is used to extract the speech features and to model the extracted features respectively. The experimental results showed significant improvement in speaker identification rates when spectral restoration based speech enhancement algorithms are used as a pre-processing step. The identification rates are found to be higher after employing the speech enhancement algorithms.

Speech enhancement based on β-order MMSE estimation of Short Time Spectral Amplitude and Laplacian speech modeling

This paper addresses the problem of speech enhancement employing the Minimum Mean-Square Error (MMSE) of β-order Short Time Spectral Amplitude (STSA). The motivation has been to take advantages of both Laplacian speech modeling and β-order cost function in MMSE estimation of clean speech. We present an analytical solution for β-order MMSE STSA estimator assuming Laplacian prior for the real and imaginary parts of the Discrete Fourier Transform (DFT) coefficients of (clean) speech. We also assume Gaussian distribution for the real and imaginary parts of the DFT coefficients of the noise. The analytical solution, named β-order LapMMSE, does not have a closed form and is highly non-linear and computationally complex. Using some approximations for the joint probability density function and the Bessel function, we also present an improved closed-form version of the estimator (called β-order ImpLapMMSE). The value of β is adapted as a function of frame Signal to Noise Ratio (SNR). We have compared the performance of the proposed estimator with the state-of-the-art estimators that assume either Gaussian or Laplacian probability density functions for the real and imaginary parts of the DFT coefficients of clean speech. To this end, the input noisy signal and the outputs of MMSE STSA, β-order STSA, and ImpLapMMSE estimators have been compared with the output of the proposed estimator. Our comparative evaluations in terms of Segmental SNR (SegSNR), Perceptual Evaluation of Speech Quality (PESQ), and Log-Likelihood Ratio (LLR) distance demonstrate the superior performance of the proposed β-order ImpLapMMSE estimator.

The importance of phase in speech enhancement

Typical speech enhancement methods, based on the short-time Fourier analysis-modification-synthesis (AMS) framework, modify only the magnitude spectrum and keep the phase spectrum unchanged. In this paper our aim is to show that by modifying the phase spectrum in the enhancement process the quality of the resulting speech can be improved. For this we use analysis windows of 32 ms duration and investigate a number of approaches to phase spectrum computation. These include the use of matched or mismatched analysis windows for magnitude and phase spectra estimation during AMS processing, as well as the phase spectrum compensation (PSC) method. We consider four cases and conduct a series of objective and subjective experiments that examine the importance of the phase spectrum for speech quality in a systematic manner. In the first (oracle) case, our goal is to determine maximum speech quality improvements achievable when accurate phase spectrum estimates are available, but when no enhancement is performed on the magnitude spectrum. For this purpose speech stimuli are constructed, where (during AMS processing) the phase spectrum is computed from clean speech, while the magnitude spectrum is computed from noisy speech. While such a situation does not arise in practice, it does provide us with a useful insight into how much a precise knowledge of the phase spectrum can contribute towards speech quality. In this first case, matched and mismatched analysis window approaches are investigated. Particular attention is given to the choice of analysis window type used during phase spectrum computation, where the effect of spectral dynamic range on speech quality is examined. In the second (non-oracle) case, we consider a more realistic scenario where only the noisy spectra (observable in practice) is available. We study the potential of the mismatched window approach for speech quality improvements in this non-oracle case. We would also like to determine how much room for improvement exists between this case and the best (oracle) case. In the third case, we use the PSC algorithm to enhance the phase spectrum. We compare this approach with the oracle and non-oracle matched and mismatched window techniques investigated in the preceding cases. While in the first three cases we consider the usefulness of various approaches to phase spectrum computation within the AMS framework when noisy magnitude spectrum is used, in the fourth case we examine the usefulness of these techniques when enhanced magnitude spectrum is employed. Our aim (in the context of traditional magnitude spectrum-based enhancement methods) is to determine how much benefit in terms of speech quality can be attained by also processing the phase spectrum. For this purpose, the minimum mean-square error (MMSE) short-time spectral amplitude (STSA) estimates are employed instead of noisy magnitude spectra. The results of the oracle experiments show that accurate phase spectrum estimates can considerably contribute towards speech quality, as well as that the use of mismatched analysis windows (in the computation of the magnitude and phase spectra) provides significant improvements in both objective and subjective speech quality – especially, when the choice of analysis window used for phase spectrum computation is carefully considered. The mismatched window approach was also found to improve speech quality in the non-oracle case. While the improvements were found to be statistically significant, they were only modest compared to those observed in the oracle case. This suggests that research into better phase spectrum estimation algorithms, while a challenging task, could be worthwhile. The results of the PSC experiments indicate that the PSC method achieves better speech quality improvements than the other non-oracle methods considered. The results of the MMSE experiments suggest that accurate phase spectrum estimates have a potential to significantly improve performance of existing magnitude spectrum-based methods. Out of the non-oracle approaches considered, the combination of the MMSE STSA method with the PSC algorithm produced significantly better speech quality improvements than those achieved by these methods individually.

Speech enhancement based on minimum mean-square error estimation and supergaussian priors

This paper presents a class of minimum mean-square error (MMSE) estimators for enhancing short-time spectral coefficients of a noisy speech signal. In contrast to most of the presently used methods, we do not assume that the spectral coefficients of the noise or of the clean speech signal obey a (complex) Gaussian probability density. We derive analytical solutions to the problem of estimating discrete Fourier transform (DFT) coefficients in the MMSE sense when the prior probability density function of the clean speech DFT coefficients can be modeled by a complex Laplace or by a complex bilateral Gamma density. The probability density function of the noise DFT coefficients may be modeled either by a complex Gaussian or by a complex Laplacian density. Compared to algorithms based on the Gaussian assumption, such as the Wiener filter or the Ephraim and Malah (1984) MMSE short-time spectral amplitude estimator, the estimators based on these supergaussian densities deliver an improved signal-to-noise ratio.