Prescribed Frequency Response Research Articles

Broadband Power Filters for Power Supply Systems with Multiphase Converters

A general method for designing broadband passive filters (BBPFs) of arbitrary order is considered. The BBPF calculation is treated as a problem of a construction of a passive LC four-pole implementing the prescribed frequency response of the input resistance. The method is based on minimizing the objective function in the space of values of reactive elements of the filter and takes into account the spectrum of current generated by the converter, as well as the frequency response of distribution network. The values of the BBPF elements of the third-fifth order have been determined. The performances of the filters obtained are compared with known options. The proposed BBPFs are demonstrated to have significant technical advantages in comparison with the known ones.

Breaking News: Verbotonal rehabilitation: Are we doing enough?

Breaking News: Verbotonal rehabilitation: Are we doing enough?

Evaluation of the Desired Sensation Level [Input/Output] Algorithm for Adults with Hearing Loss: The Acceptable Range for Amplified Conversational Speech

This study had two related purposes: first, to define the range of optimal ear canal levels of aided speech in both high frequency and low frequency regions for adults, using both subjective and objective definitions of optimal; and second, to determine whether a prescribed frequency response, such as that given by Desired Sensation Level [Input/Output], falls within the adult listener's optimal range. Twenty-three adult listeners with mild to moderately severe sensorineural hearing loss were selected from a pool of research volunteers. They were fitted in the laboratory with the Siemens Signia hearing instrument and tested with 20 nominally different frequency responses. All advanced processing options of the hearing instrument were disabled. Subjective ratings of loudness and quality and objective measures of consonant identification were obtained for every frequency response. These adult listeners had, on average, a 10 dB range of measured responses in both the low and the high frequencies that resulted in optimal performance on all the measurements. The range did not vary with degree or configuration of hearing loss, or previous hearing aid experience. Desired-Sensation-Level Input/Output targets were within the optimal range for the low frequencies, and 3 dB above the optimal range for the high frequencies. A range of aided ear canal frequency responses was determined within which adults with mild to moderately severe hearing loss performed optimally on both objective and subjective outcomes. Clinical implications of this finding include the following: prescriptive methods providing different targets may all result in optimal fittings; and a range of targets may be more appropriate than a single target when setting the frequency-gain characteristics of the hearing instrument.

Application of the differential-evolution strategy to the design of frequency-selective surfaces

An optimization approach based on the diffential evolution strategy (DES) is applied to the design of frequency-selective surfaces (FSS). The spectral Galerkin method is used to analyze the electromagnetic scattering from a FSS screen while DES is used to tune the FSS unit-cell dimensions and dielectric properties in order to achieve the prescribed frequency responses. The DES is compared to the real-coded genetic algorithm. The simulated results of FSS dipole arrays are presented, which demonstrate that DES is a more simple, yet more efficient and more robust, method for the design of FSS. © 2005 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2005.

Design of Stable IIR Digital Filter Based on Least<tex>$rm P$</tex>-Power Error Criterion

In this paper, the least p-power error criterion is presented to design digital infinite impulse response (IIR) filters to have an arbitrarily prescribed frequency response. First, an iterative quadratic programming (QP) method is used to design a stable unconstrained one-dimensional IIR filter whose optimal filter coefficients are obtained by solving the QP problem in each iteration. Then, the proposed method is extended to design constrained IIR filters and two-dimensional IIR filters with a separable denominator polynomial. Finally, design examples of the low-pass filter are demonstrated to illustrate the effectiveness of the proposed iterative QP method.

Audiometric configurations of hearing impaired children in Hong Kong: implications for amplification

Purpose: Children with hearing loss who require special school placement may have a wide range of audiometric configurations. Since such children will vary in auditory status their amplification requirements may also be diverse. This study examined the audiological records of 231 children attending four schools for hearing impaired children in Hong Kong to gain an understanding of common audiometric patterns found in the school children and their auditory rehabilitation needs. Method: Data on the children's aetiology of hearing loss, hearing status, tympanometric findings and the electroacoustic characteristics of their hearing aids were obtained. For 424 children's ears considered having essentially sensorineural hearing loss, k-means cluster analysis methods were used to categorize audiometric configuration groups Results: Cluster analysis that indicated that five distinct audiometric configurations could be found among the school children. Different clusters contained children who had differing amplification needs. The study analysed a number of parameters to check fitting outcomes, including average prescribed gain, frequency-specific measured versus prescribed gain, prescribed frequency response, measured versus prescribed frequency response and the predicted aided thresholds for the children. Conclusion: The amplification needs associated with these five configurations, including recommended prescription gain, maximum power output and possible signal processing strategies, were considered. The clustering algorithm approach proved useful as a means of grouping distinctive audiometric profiles.

Traveling-wave amplifiers with prescribed frequency response

Microwave transistor amplifier combinations that have controlled frequency response over a specified bandwidth were designed. Theoretical analysis of such an amplifier with an arbitrary number of sections is presented. The response of the amplifier is controlled by tapering the frequency selectivity or Q of each section of the amplifier. To verify the theory, a three-section amplifier with maximally flat time delay response was designed, constructed, and evaluated. Existing traveling-wave amplifiers were modeled as lossy transmission lines. Although the amplifiers were relatively broadband, a prescribed frequency response was not achieved, and each transistor did not receive an equal portion of the signal power. Resistive elements were required for impedance matching at the input and output. The design seeks to improve on previous techniques by trading bandwidth for controlled gain. By making the transmission line that connects the amplifier sections nonuniform, the frequency response was controlled over the design bandwidth. The designs can easily be implemented using familiar components.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Microwave bandpass filters using series-cascaded sections of microstrip line

A quarter-wavelength-coupled filter with prescribed frequency response is presented which uses a novel configuration of series-cascaded microstrip lines as its resonating components. Design equations are obtained from ABCD parameters, with approximations taken to account for the double resonance characteristics of the filter's constituent networks. Experimental and theoretical results agree closely.

Broadband sound absorbers based on the mean-value theory.

The mean-value theory was developed by Professor Skudrzyk as a method for predicting and understanding the dynamic response of complex vibratory structures, like plates and shells [E. J. Skudrzyk, J. Acoust. Soc. Am. 67, 1105–1135 (1980)]. In this work he refers to the application of the theory to ‘‘situations that call for prescribed frequency response with a small number of resonators, e.g., matching absorbers to the wave resistance of the medium’’ [E. J. Skudrzyk, Acustica 64, 123–147 (1987)]. This paper will review the salient features of the mean-value theory and elaborate on how the author and Professor Skudrzyk applied the theory to the design of broadband sound absorbers.

Hearing Aid Gain for Loudness-Density Normalization in Cochlear Hearing Losses with Impaired Frequency Resolution

A theoretical criterion for preliminary prescription of hearing aid gain and frequency response was formulated on the basis of Zwicker's loudness model, modified for impaired auditory frequency resolution in cochlear hearing losses. The procedure was designed to restore normal relative loudness contributions from each frequency band of input speech. Prescribed frequency responses had less steep bass cut than recommended by either the Prescription of Gain/Output or the National Acoustic Laboratories' procedures, regardless of various model assumptions. Prescribed overall gain depended on the loudness growth assumed in the model. In cases where auditory filters are wider than normal and loudness recruitment is complete, the procedure yielded a nonlinear relation between hearing aid gain and hearing loss: Required insertion gain (in dB) was 25 to 30% of hearing threshold loss (in dB HL) for mild to moderate losses, but this percentage increased for more severe impairments. For cases with incomplete loudness recruitment, the model prescribed that insertion gain should be 40 to 50% of hearing threshold loss for a wide range of impairments.

The National Acoustic Laboratories' (NAL) new procedure for selecting the gain and frequency response of a hearing aid.

A new procedure is presented for selecting the gain and frequency response of a hearing aid from pure-tone thresholds. This was developed from research which showed that a previous procedure did not meet its aim of amplifying all frequency bands of speech to equal loudness but that frequency responses which did so were considerably more effective. Measurements of 30 sensorineurally hearing-impaired ears (27 subjects), together with data from other studies, were analyzed to determine the best formula for predicting the optimal frequency response, for each individual, from the audiogram. The analysis indicated that a flat audiogram would require a rising frequency response characteristic of about 8 dB/octave up to 1.25 kHz and thereafter a falling characteristic of about 2 dB/octave. Variations in audiogram slope required about one-third as much variation in response slope. Three frequency average (3FA) gain was calculated to equal the 3FA gain of the previous procedure. Forty-four subjects (67 aided ears) fitted by the new procedure were evaluated by paired comparison judgments of the intelligibility and pleasantness of speech. The prescribed frequency response was seldom inferior to, and usually better than, any of several variations having more, or less, low and/or high-frequency amplification. On the average, used gain was approximately equal to prescribed gain. It is concluded that the new formula should prescribe a near optimal frequency response with few exceptions.

Inverse scattering for optical couplers. Exact solution of Marchenko equations

An exact solution of Marchenko equations for rational scattering data of arbitrary order is developed, with reference to the case of two coupled waves propagating in a lossless (optical) waveguide. Some numerical examples are presented for the synthesis of coupling structures having a prescribed frequency response.

Two-dimensional recursive filter design--A spectral factorization approach

This paper concerns development of an efficient method for the design of two-dimensional (2-D) recursive digital filters. The specific design problem addressed is that of obtaining half-plane recursive filters which satisfy prescribed frequency response characteristics. A novel design procedure is presented which incorporates a spectral factorization algorithm into a constrained, nonlinear optimization approach. A computational implementation of the design algorithm is described and its design capabilities demonstrated with several examples.

Synthesis of recursive digital filters using the minimum p-error criterion

The problem of designing a stable recursive digital filter to have an arbitrarily prescribed frequency response may be considered as an approximation problem. Using the minimum <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">p</tex> - error criterion, a new problem of minimizing a function of <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">n</tex> variables results, which is successfully solved using the Fletcher-Powell algorithm. An important theorem guaranteeing the existence of a stable optimum for a large class of synthesis problems is stated, and necessary modifications to the Fletcher-Powell algorithm to assure stability are considered. Finally a number of results of the application of this method are given.