Prem C. Pandey

Dichotic presentation of speech signal with critical band filtering for improving speech perception

The reduction in the frequency resolving capacity of the auditory system due to the spread of masking of frequency components by neighboring components degrades speech perception in cases of sensorineural hearing impairment. We have carried out an experimental evaluation of splitting speech into two signals by using a bank of critical band filters, in order to reduce the effect of spectral masking in the cochlea. The dichotically presented signals are perceptually integrated in the auditory cortex. Listening tests were carried out with vowel-consonant-vowel and consonant-vowel syllables for twelve English consonants on five normal hearing subjects with simulation of sensorineural impairment done by adding white masking noise to the speech signal at various SNRs. Significant improvements in the recognition score were obtained under adverse listening conditions. An improvement in the reception of speech feature of voicing, place, and manner was observed in information transmission analysis.

Enhancement of alaryngeal speech using spectral subtraction

The transcervical electrolarynx is of great help to persons who cannot use their natural voice production mechanism. The device is held against the neck, and the vibrations generated move up the vocal tract to produce useful speech. The presence of background noise, caused by leakage of the acoustic energy from the vibrator, degrades the resulting speech. After formulating a theoretical basis, modified spectral subtraction method is used for speech enhancement. The average magnitude spectrum of noise, obtained with lips closed in the training mode, is subtracted from the magnitude spectrum of the noisy speech and the signal is reconstructed using the original phase spectrum. It is observed that effective noise cancellation is obtained, if the noise estimation and subtraction is done using 2-pitch frames. The set of optimal values for processing parameters of the method are empirically obtained.

Binaural dichotic presentation to reduce the effects of spectral masking in moderate bilateral sensorineural hearing loss.

Abstract Objective: The objective of the study was to evaluate the effectiveness of binaural dichotic presentation using comb filters with complementary magnitude responses, based on fixed bandwidth and auditory critical bandwidth, in improving speech perception by persons with moderate bilateral sensorineural hearing loss, and to assess its effect on localization of the sound source. Design and Study sample: Listening tests involving consonant recognition and source direction identification were conducted on six normal-hearing subjects under simulated hearing loss and on eleven subjects with moderate bilateral sensorineural loss in quiet. Results: The tests on normal-hearing subjects showed higher recognition scores and smaller response times for the comb filters based on the auditory critical bandwidth. The tests using these comb filters on the hearing-impaired subjects resulted in an increase of 14%–31% (mean: 22%) in recognition scores and a significant decrease in response times, with no significant effect on the identification of the direction of broadband sound sources. Conclusions: The results show that dichotic presentation may be useful for speech processing in binaural hearing aids.

Dichotic presentation of speech signal using a critical filter bank for bilateral sensorineural hearing impairment

Sensorineural hearing‐impaired listeners face a particular problem in view of a decrease in the frequency resolving capacity of an ear due to the spread of masking of frequency components by adjacent frequency components. Filtering a speech signal by a bank of critical band filters and adding signals from alternate bands for presenting to the two ears is likely to reduce the effect of the spread of masking along the cochlear partition, and thus may help in improving the speech intelligibility. This processing scheme has been implemented with 18 critical bands for experimental evaluation through listening tests. The scheme was found to be helpful in improving recognition scores and transmission of speech features in listening tests with normal hearing subjects with simulated sensorineural hearing loss. Listening tests were carried out using 12 vowel–consonants–vowel and consonant–vowel nonsense syllables presented in quiet (no masking noise), on ten subjects with mild to very severe sensorineural hearing l...

A wavelet based technique for suppression of EMG noise and motion artifact in ambulatory ECG

A wavelet-based denoising technique is investigated for suppressing EMG noise and motion artifact in ambulatory ECG. EMG noise is reduced by thresholding the wavelet coefficients using an improved thresholding function combining the features of hard and soft thresholding. Motion artifact is reduced by limiting the wavelet coefficients. Thresholds for both the denoising steps are estimated using the statistics of the noisy signal. Denoising of simulated noisy ECG signals resulted in an average SNR improvement of 11.4 dB, and its application on ambulatory ECG recordings resulted in L2 norm and max-min based improvement indices close to one. It significantly improved R-peak detection in both the cases.

Wavelet Based Cancellation of Respiratory Artifacts in Impedance Cardiography

Impedance cardiography is a noninvasive technique for monitoring stroke volume, based on sensing variation in the thoracic impedance, z(t), due to blood flow. In this technique, first derivative of impedance, dzjdt, is used to calculate two parameters: ventricular ejection time and (-dzjdt)max. Respiration and motion artifacts cause base line drift in the sensed impedance waveform, particularly during exercise, and this drift results in errors in the estimation of the two parameters. Ensemble averaging of dz/dt signal suppresses respiratory and motion artifacts but it introduces distortion in the signal. In this study, a wavelet based denoising method is used to cancel corrupting respiratory artifacts from the dz/dt and z(t) signals in order to make a reliable estimate of cardiac output.

Multi-band frequency compression for improving speech perception by listeners with moderate sensorineural hearing loss

In multi-band frequency compression, the speech spectrum is divided into a number of analysis bands, and the spectral samples in each band are compressed towards the band center by a constant compression factor, resulting in presentation of the speech energy in relatively narrow bands, for reducing the effect of increased intraspeech spectral masking associated with sensorineural hearing loss. Earlier investigation assessing the quality of the processed speech showed best results for auditory critical bandwidth based compression using spectral segment mapping and pitch-synchronous analysis-synthesis. The objective of the present investigation is to evaluate the effectiveness of the technique in improving speech perception by listeners with moderate to severe sensorineural loss and to optimize the technique with respect to the compression factor. The listening tests showed maximum improvement in speech perception for a compression factor of 0.6, with an improvement of 9%-21% in the recognition scores for consonants and a significant reduction in response times.

Estimation of Place of Articulation During Stop Closures of Vowel–Consonant–Vowel Utterances

Production of vowel-oral stop consonant-vowel utterances involves movement of articulators from the articulatory position of the initial vowel towards that of the oral stop closure, and then to that of the final vowel. As the closure segments have zero or low signal energy, linear predictive coding (LPC)-based estimation of vocal tract shape fails during stop closure. This paper reports a technique for estimation of place of articulation during stop closures by performing bivariate polynomial modeling on vocal tract area values during transition segments preceding and following the closure. The technique with second-degree polynomial modeling was found to be suitable for estimating the place of maximum constriction during stop closure segments of vowel-consonant-vowel utterances with bilabial, alveolar, and velar stops. The estimated places compared well with the actual constriction locations observed from the articulatory data. The technique may be useful for improving effectiveness of speech-training aids for production of stop consonants by providing visual feedback of the estimated place of articulation.

Speech enhancement using spectral subtraction and cascaded-median based noise estimation for hearing impaired listeners

A spectral subtraction technique is presented for real-time speech enhancement in the aids used by hearing impaired listeners. For reducing computational complexity and memory requirement, it uses a cascaded-median based estimation of the noise spectrum without voice activity detection. The technique is implemented and tested for satisfactory real-time operation, with sampling frequency of 12 kHz, processing using window length of 30 ms with 50% overlap, and noise estimation by 3-frame 4-stage cascaded-median, on a 16-bit fixed-point DSP processor with on-chip FFT hardware. Enhancement of speech with different types of additive stationary and non-stationary noise resulted in SNR advantage of 4 – 13 dB.

Controlled synthesis of functional Ag, Ag–Au/Au–Ag nanoparticles and their Prussian blue nanocomposites for bioanalytical applications

In this work, we report a facile approach to synthesize processable silver nanoparticles (AgNPs), bimetallic nanoparticles (Ag–Au/Au–Ag) and a decorated Prussian blue nanocomposite (PB–AgNP). The presence of cyclohexanone/formaldehyde facilitates the formation of functional AgNPs and Ag–Au/Au–Ag from 3-aminopropyltrimethoxysilane (3-APTMS) and the respective capped noble metal ions. The use of the aforementioned reducing agents (3-APTMS and cyclohexanone) also enables the synthesis of polycrystalline Prussian blue nanoparticles (PBNPs). As synthesized PBNPs, AgNPs and Au–Ag enable the formation of nano-structured composites (PB–AgNP, PB–Au–Ag) displaying better catalytic activity than that recorded with natural enzyme. The nanomaterials have been characterized by UV-vis, FT-IR and Transmission Electron Microscopy (TEM) with the following major findings: (1) 3-APTMS capped silver ions in the presence of suitable organic reducing agents [3-glycidoxypropyltrimethoxysilane (GPTMS), cyclohexanone and formaldehyde] are converted into AgNPs under ambient conditions, (2) the time course of the synthesis and dispersibility of the nanoparticles are found to be a function of the organic reducing agents, (3) the use of formaldehyde and cyclohexanone in place of GPTMS with 3-APTMS outclasses the other two in imparting better stability to amphiphilic AgNPs with reduced silanol content, (4) an increase in 3-APTMS concentrations causes a decrease in the nanogeometry of AgNPs, (5) the simultaneous synthesis of bimetallic nanoparticles under desired ratio of silver and gold cations are recorded, (6) cyclohexanone mediated synthesis of AgNPs and Ag–Au/Au–Ag enable the formation of a homogeneous nanocomposite with PBNP as a peroxidase mimetic representing a potential substitute of peroxidase enzyme. The peroxidase mimetic ability has been found to vary as a function of the 3-APTMS concentration, revealing the potential role of functional silver nanoparticles in bioanalytical applications.