Sheau Fang Lei

The cubic distortion product otoacoustic emissions from the normal and noise-damaged chinchilla cochlea

A normative study of the cubic distortion product emissions from 104 monaural and binaural chinchillas was undertaken to establish criteria upon which noise exposed animals could be evaluated. From this normative group, 47 randomly selected chinchillas were exposed to various high level (150-, 155-, and 160-db peak SPL) impulse noises. Auditory evoked potentials and cubic distortion product otoacoustic emissions were measured on each animal pre- and post-exposure and related to the sensory cell populations 30 days post-exposure. Both group mean and individual animal data indicated that the distortion product emissions were more sensitive, frequency-specific indices of noise-induced cochlear effects than pure-tone threshold measures. This was particularly evident near the threshold for noise-induced damage to the outer hair cell system.

Audiometric and histological differences between the effects of continuous and impulsive noise exposures

An experiment was designed to determine if, for equal SPL and power spectrum, the effects on hearing of high-kurtosis noise exposures and a Gaussian noise exposure are different and the extent to which any differences measured in terms of audiometric and histological variables are frequency specific. Three groups of chinchillas with 10 animals/group were exposed for 5 days at 90 dB SPL to one of three types of noise, each with the same power spectrum. The impulsiveness, defined by the kurtosis, and the region of the spectrum from which the impulsive components of the noise were created differed for two of the noises, while the third was a continuous Gaussian noise. The results show that the most impulsive noise produced up to 20 dB greater permanent threshold shift at the high frequencies than did the Gaussian noise exposure. However, these audiometric results were difficult to reconcile with the pattern of sensory cell losses that showed statistically significant larger losses of outer hair cells for the impulsive exposure in the 0.25-kHz region. When the impacts in a high-kurtosis noise were created from the energy in the 1- through 6-kHz region of the spectrum, the audiometric profile of hearing loss was similar to that produced by the Gaussian noise; however, inner hair cell losses were significantly greater in the 4-kHz octave band region of the cochlea.

The application of frequency and time domain kurtosis to the assessment of hazardous noise exposures

Five computer-synthesized broadband noises, each having the same average spectrum and the same unweighted Leq of 100 dB SPL but very different temporal structures, were used to produce hearing loss in chinchillas. Despite the same exposure energies and spectra, each noise exposure produced a different magnitude and frequency distribution of hearing loss and sensory cell loss. The results indicate that the statistical properties of a signal are important in the determination of hearing loss. When the audiometric and histological results are compared to a metric based upon kurtosis measured in the time and the frequency domain for each exposure, there is a clear indication that these statistical metrics are good predictors of the relative magnitude and frequency distribution of the acoustic trauma.

Hearing threshold shifts from repeated 6‐h daily exposure to impact noise

Exposure of chinchillas to broadband, high-level impact noise on an interrupted 6-h daily schedule over 20 days has shown that pure-tone thresholds measured immediately following each daily exposure improve as much as 30 dB despite the continuing noise exposure. The time constant of this recovery effect (toughening) and the magnitude of the effect are related to the audiometric test frequency and the exposure energy. The trauma, quantified by permanent threshold shifts and sensory cell losses, produced by the interrupted exposure paradigm is generally less than that produced by an equal-energy uninterrupted exposure. The wide variations in the temporal pattern of threshold shift across similarly exposed animals suggest that the toughening effect reflects the underlying susceptibility of that animal to noise trauma.

Low Computational Complexity, Low Power, and Low Area Design for the Implementation of Recursive DFT and IDFT Algorithms

A novel recursive algorithm for discrete Fourier transform (DFT) and its inverse transform (IDFT) is proposed in this brief. It was found that the proposed algorithm and its implementation outperformed other existing recursive algorithms. The proposed algorithm was found to 1) reduce multiplication computations by 50.5% using the symmetric identity of coefficients and a resource-sharing technique and register-splitting scheme; 2) decrease read-only memory sizes by 50% compared with conventional algorithms; 3) reduce the number of multipliers implemented by 80% compared with the latest algorithm; and 4) increase data throughput by 100% per transformation. This design is suitable for communication systems and digital radio mondiale (DRM) systems, such as dual-tone multifrequency detection and coded orthogonal frequency-division-multiplexing modulation. The algorithm was designed and fabricated using a 0.18 ¿m 1P6M complementary metal-oxide-semiconductor process. The core area is 397 × 388 ¿m2, including the DFT and IDFT modules. For modern applications (voice over packet and DRM), this processor only consumes 2.96 mW at 25 MHz. Furthermore, it can calculate the 212/165/106/288/256/176/112-point DFTs and IDFTs.

Common Architecture Design of Novel Recursive MDCT and IMDCT Algorithms for Application to AAC, AAC in DRM, and MP3 Codecs

This paper presents a novel recursive algorithm to compute the modified discrete cosine transform (MDCT) and the inverse MDCT (IMDCT) based on type IV of the discrete cosine transform (DCT-IV) algorithm. The proposed algorithm has the following advantages: In contrast with parallel designs, the input sequence fed by serial in/serial out (SISO) can dynamically be switched with the variable window length. The data throughput per transformation for the MDCT and IMDCT algorithms is four times higher than that of the previous algorithms, and the ROM size can be reduced by 50%-79%. Less memory is required for accessing; thus, it can reduce the chip area in hardware implementation. The chip efficiency is also increased, and the proposed architecture makes a feasible design to integrate several audio standards [i.e., advanced audio coding (AAC)/AAC in digital radio mondiale (DRM/MPEG-1 Audio Layer 3 (MP3)] into one portable media player. The proposed algorithm is designed and fabricated by using 0.18-mum 1P6M complimentary metal-oxide-semiconductor (CMOS) process. The core area is 441 times 437 mum2, including the MDCT, IMDCT, and DCT-IV modules. For modern audio applications, i.e., AAC/AAC in DRM/MP3, this processor only consumes 14.077/3.482/0.3138 mW at 50/12.5/1 MHz. Furthermore, the proposed algorithm can calculate the 2048/1920/256/240/36/12-point MDCT and the 1024/960/128/120/18/6-point IMDCT.

Speech enhancement for nonstationary noises by wavelet packet transform and adaptive noise estimation

This paper proposes a speech enhancement algorithm based on wavelet packet transform and adaptive noise estimation. The wavelet threshold in this algorithm is temporally adapted to SNR variations which can be calculated by adaptive noise estimation. Adaptive noise estimation can be computationally simple and reliable to estimate the noise levels from noisy signal itself without complicated speech pause detection. Thus the proposed algorithm can efficiently suppress the noise while reducing speech distortion. A speech signal corrupted by nonstationary noises is used for the performance evaluation of the proposed algorithm. Experimental results show that the proposed algorithm outperforms the conventional spectral subtraction and other wavelet based denoising approaches for speech enhancement.

Design of a Low Power Architecture for CABAC Encoder in H.264

In this paper, we propose a low power architecture for the implementation of context based adaptive binary arithmetic coding (CABAC) system in H.264. CABAC needs to have the accurate probability estimations for most probable symbol (MPS) to enhance higher compression ratio. This data compression efficiency can be implicitly achieved by iteratively updating probability models stored in the embedded memory for hardware design. Therefore the design of the memory hierarchy and the suitable architecture is an important issue so that the power consumption can be kept low caused by memory accesses for iteratively executing arithmetic coding operations. To address the low power consideration for designing a CABAC encoder, we propose the architecture by using variable length tag cache memory scheme and pipeline structure. The simulation results show that our proposed architecture can achieve 50% power consumption saving, and throughput can be higher than 200Mbps

Low-Computation-Cycle, Power-Efficient, and Reconfigurable Design of Recursive DFT for Portable Digital Radio Mondiale Receiver

Low-cost, fast-computational, power-efficient, and reconfigurable design for recursive discrete Fourier transform (RDFT) is proposed in this brief. The proposed method is the first integration that collated both the prime factor algorithm (PFA) and the Chinese reminder theorem (CRT) into a recursive algorithm. Hence, a multicycle RDFT algorithm (PFA + CRT + RDFT) and its hardware implementation are produced and presented here in great detail. Compared with some well-known recursive algorithms, the significant improvements for the proposed algorithm can be summarized as follows: 1) The number of computational cycles of the proposed algorithm can be saved by up to 88.5%; 2) The number of multiplications and additions for the proposed algorithm is dramatically reduced by up to 85.2% and 85.2%, respectively; 3) The amount of coefficient read-only memory for storing the twiddle factors totally takes 694 words fewer than those of other existing RDFT algorithms; 4) The hardware cost of the proposed algorithm only takes four real multipliers and eight real adders. This design is more suitable for digital radio mondiale (DRM) systems, such as coded orthogonal frequency-division-multiplexing modulation. The proposed RDFT algorithm was designed and fabricated using a 0.18-μm 1P6M CMOS process. The core area is 521 × 508 μm2, and this hardware accelerator only consumes 8.44 mW at 25 MHz. Furthermore, the performance index of power for this design is three times discrete Fourier transform (DFT) per energy of previous work. Additionally, it can calculate the 288/256/176/112-point DFTs for a portable DRM receiver.

Low Complexity and Fast Computation for Recursive MDCT and IMDCT Algorithms

Fast algorithms are derived for modified discrete cosine transform (MDCT) and inverse MDCT (IMDCT) in this brief. The proposed algorithms based on type II discrete cosine transform and type II discrete sine transform not only adopt a unified architecture for both MDCT and IMDCT computations but also take only N/8 + 1 computational cycles for each output sequence. Compared with previous IMDCT approaches, the number of preprocessing multiplications of the proposed IMDCT algorithm is reduced by 87.5%. In addition, the coefficient requirements for preprocessing in the proposed IMDCT algorithm can be reduced by 50%, and the number of multiplications for the recursive kernel is greatly decreased by up to 87.5%. The proposed algorithms in terms of hardware costs take two fewer multipliers and six fewer adders than some well-known recursive algorithms. Therefore, the proposed architecture is better suited for various audio codecs.