Audio Frequency Range Research Articles

Design and Development of Non-Linearly Controlled Class-D Audio Amplifier

A systematic and simple approach to develop a 20 W audio frequency range switch mode amplifier is presented in this paper. A non-linear sliding mode (SM) technique-based low cost analog controller enables the realized amplifier to deliver highly linear and efficient operation throughout the audio frequency spectrum. The theoretical aspects and practical limitations in the design and realization of subsystems, such as the signal conditioning stage, power stage and sliding mode controller, are considered, while the viable solution is also stated and justified. The hardware realization scheme is also elaborated, based on which the laboratory prototype is fabricated. Hardware results with a 4 Ω resistive load are given on which the performance of the amplifier is evaluated. The total harmonic distortion (THD) below 1% and 73% efficiency at peak load make the amplifier well suited for high quality audio application.

In-Phase and Quadrature-Phase Sinusoidal Signal Generation Using DDS Technique

In-phase and quadrature-phase (IQ) sinusoidal signals are used as bases functions in many phase modulation schemes in communication systems. Generating such signals in engineering education laboratories without higher-end signal generators is quite challenging. Most of the time, the IQ signals used in undergraduate engineering education laboratories are in audio frequency range that is used to demonstrate or experiment with various phase modulation schemes. This paper presents a method to generate IQ sinusoids in the audio frequency range using direct digital synthesis technique. The system developed is simulated using MathWorks® Simulink and implemented on commonly available Xilinx’s® Spartan 6 FPGA. The system designed is capable of producing phase correct sine and cosine waves having frequencies between 1 Hz and 20 kHz.

The acoustical properties of tetraethyl orthosilicate based granular silica aerogels.

Available data suggests that granulated aerogels can be of interest in terms of their sound absorption performance in the audio frequency range. However, there is still no thorough understanding of the complex physical phenomena which are responsible for their observed acoustical properties. This work is an attempt to address this gap through advanced material characterization methods and mathematical modelling. Aerogel samples are produced through a two-step, acid-base sol-gel process, with sol silica concentration and density being the main variables. Their pore structure is carefully characterized by nitrogen sorption analysis and scanning electron microscopy. The acoustical properties of hard-backed granular silica aerogels are measured in an impedance tube and the results predicted accurately with the adopted theoretical model. Although silica aerogels have over 90% of open interconnected pores, this was neither reflected in the measured acoustical properties nor the parameter values predicted with the model. Novel results show that only a proportion of the micro and mesopores in the direct vicinity of the grain surface influenced the acoustical properties of aerogels. Further work in the hierarchical pore structure of aerogels is required to better understand the roles of different pore scales on the measured acoustical properties of a granulated aerogel.

Sound energy harvesting by leveraging a 3D-printed phononic crystal lens

We investigate the harvesting of sound waves by exploiting a 3D-printed gradient-index phononic crystal lens. The concept is demonstrated numerically and experimentally for focusing audio frequency range acoustic waves in air to enhance sound energy harvesting. A finite-element model is developed to design the unit cell dispersion properties and to construct the 3D lens for wave field simulations. Numerical simulations are presented to confirm the focusing of incident plane waves and to study the sensitivity of the refractive index profile to the direction of wave propagation. The theoretical predictions are validated experimentally using a scanning microphone setup under speaker excitation, and a very good agreement is observed between the experimental and numerical wave fields. A circular piezoelectric unimorph harvester is placed at the focal position of the lens, and its performance is characterized with a resistor sweep in the absence and presence of the lens, resulting in more than an order of magnitude enhancement in the harvested power with the lens. The 3D-printed lens presented here substantially enhances the intensity of sound energy via focusing, yielding micro-Watt level power output, which can find applications for wireless sensors and other low-power electronic components.

Modeling kaolinite electrical features under pressure using Pseudo Random Renormalization Group method at the audio frequency range

Few reports are displayed on relation between electrical characteristics of rocks and pressure. The objective of this article is the interpretation and modeling of experimental kaolinite specimens under various pressures (0- ~4.5 Kb, at ~50% humidity), and frequency (10 Hz - 10 kHz). Complex impedance measurements were performed for samples. At low pressure range (≤1 Kb); the reliance of the experimental capacitance and conductance on the pressure displays a considerable dependence on the applied pressure. Constant conductances are present at higher pressures. With rising pressure the capacitance decreases. These behaviors are interpreted by percolation theory. With the rise of pressure, the pore spaces decrease and conducting paths between grains increase. The behavior of capacitance and conductance with frequency is comparable with other reports as it will be discussed. Due to existence of water, it was supposed there is impedance at the kaolinite grain surfaces. Also, it was supposed the presence of charge movement and chemical reaction at surface grains. Renormalization group model as a member of the percolation group methods was used to interpret and model experimental data. We developed a model using four phases to analyze the probable deviations in electrical features that may control pressure.

Investigation on Electrical Properties of Solid Polymer Sheets (HDPE AND LDPE) at Audio Frequency Range

Two different groups of solid polymer sheets: low density polyethylene (LDPE) sample of thickness 0.006 cm and 0.007 cm along with high density polyethylene (HDPE) sample of the thickness of 0.009 cm, 0.010 cm were taken in this work. The measurement of electrical properties such as dielectric constant, ε' and dielectric loss, ε'' for LDPE and HDPE polymer sheets have been measured using a dielectric cell. The dielectric cell has been fabricated which consists of two circular parallel plates of pure stainless steel each of 5 cm diameter and 2 mm thickness. An impedance bridge (GRA 650A) was used for measurement of capacitance, C, and dissipation factor, D in the audio frequency (AF) range, 100 Hz to 10 kHz. Different samples were loaded in between the two plates of the cell and the capacitance as well as the dissipation factor were estimated from the dial readings of the bridge. Effect of frequency variation on ε', ε'', relaxation time, τ , dissipation factor, tanδ and ac conductivity, σ were also discussed at audio frequency range. The complex permittivity, ε*, related to free dipole oscillating in an alternating field and loss tangent, tanδ were calculated. The frequency-dependent conductivity, dielectric behavior, and electrical modulus, both real (M') and imaginary (M") parts of LDPE and HDPE have been studied in this work. The values of the real part of the electrical modulus (M') did not equal to zero at low frequencies and it is expected that the electrode polarization may develop in both sheets. These findings reveal an increased coupling among the local dipolar motions in a short-range order localized motion. The analysis of real (ε') and imaginary (ε'') parts of dielectric permittivity and that electrical modulus real (M') and imaginary (M") parts signify poly dispersive nature of relaxation time as observed in Cole-Cole plots.

Performance Study of a Digitally Assisted Impedance Bridge on the Basis of Capacitance Measurements in the Audio Frequency Range

A digitally assisted (DA) coaxial bridge, mainly consisting of a ratio transformer and digital voltage sources, was set up in a four-terminal-pair (4-TP) configuration for precision impedance ratio measurements. A 10:1 capacitance ratio was then measured in the range of 1 pF– $1~ {\mu }\text{F}$ mainly at 1 kHz using the 4-TP DA bridge, and the results were compared to those from the existing two-terminal-pair (2-TP) and three-terminal (3-T) capacitance bridges. The deviations between the capacitance ratio measurements obtained by the different bridges lie from a few parts between 108 and 105, depending on the measurement capabilities of the 2-TP/3-T bridges. Moreover, the measurement frequency of the 4-TP bridge was varied from 50 Hz to 20 kHz, and the frequency dependence of the 10:1 capacitance ratio was studied and compared with the reference ratios. The verification results showed that the existing 2-TP/3-T bridges can be replaced by the new 4-TP DA bridge with an extended measurement range and better uncertainty for capacitance measurements.

Enhancing the dielectric properties of activated bamboo charcoal under the exposure of DC glow discharge plasma

The capability of energy storage capacity to be determined by the surface properties of the material and the surface properties of the material enhanced by the exposure of DC glow discharge Plasma. The Bamboo Charcoal (BCC) was synthesized and activated by Pyrolysis process. The Activated BCC was exposed to DC glow discharge Plasma with an applied potential of 450 V DC to enhance the surface properties. The XRD, FTIR and SEM were utilized to characterize the crystalline nature and surface properties of Plasma treated and untreated BCC. The dielectric properties of the samples were analysed at room temperature. The results report that the Plasma treated BCC dielectric properties was enhanced in the audio frequency range.

Synaptic transistors with aluminum oxide dielectrics enabling full audio frequency range signal processing

The rapid evolution of the neuromorphic computing stimulates the search for novel brain-inspired electronic devices. Synaptic transistors are three-terminal devices that can mimic the chemical synapses while consuming low power, whereby an insulating dielectric layer physically separates output and input signals from each other. Appropriate choice of the dielectric is crucial in achieving a wide range of operation frequencies in these devices. Here we report synaptic transistors with printed aluminum oxide dielectrics, improving the operation frequency of solution-processed synaptic transistors by almost two orders of magnitude to 50 kHz. Fabricated devices, yielding synaptic response for all audio frequencies (20 Hz to 20 kHz), are employed in an acoustic response system to show the potential for future research in neuro-acoustic signal processing with printed oxide electronics.

THE EFFECT OF FREQUENCY VARIATION ON DIELECTRIC CONSTANT OF RAPHIA HOOKERI

This work sought to investigate the effect of varying the frequency of an applied electric field on the dielectric constant of raphia hookeri. The aim of the work was to ascertain the suitability of using the sample for engineering applications. It was revealed, from the recorded results, that the dielectric constant of the sample decays exponentially with frequency. Also, greater degree of polarisation was observed with decrease in frequency. Again, as a good thermal insulator, it was revealed that the values of the sample’s dielectric constant compared favourably with those of commonly used conventional dielectric materials. Thus, it is obvious that if put into production cycle, the sample can serve as a low-cost and environmentally friendly material suitable for engineering applications within audio frequency range. This will, in turn, help to provide raw material for electronic industry and also improve the economy.

Moisture content dependence of anisotropic vibrational properties of wood at quasi equilibrium: analytical review and multi-trajectories experiments

Abstract This article aims at providing a synthetic view of the equilibrium moisture content (EMC) dependence of wood vibrational properties (i.e. dynamic mechanical properties in the audio-frequency range), including specific dynamic modulus of elasticity (E′/γ) and damping coefficient expressing internal friction (tanδ). A series of multi-trajectories experiments was designed to complete an analytical review. Literature indicates that: (1) in longitudinal (L) direction, the EMC dependence of E′/γ shows a very consistent shape (rather linear) between studies, while its shape is non-linear for tanδ and varies significantly between studies; (2) EMC dependence of tanδ is rather well documented in the L direction, in adsorption, for softwoods, but data covering EMC dependence in both L and other anisotropic directions, and sorption hysteresis, are still scarce. Experiments were conducted on a softwood (spruce) and a hardwood (maple), in L and radial (R) directions, in full adsorption from oven-dry state, full desorption from water-saturated state, and relative humidity (RH) loops without extreme conditioning. Measurements were made at conditions considered “at equilibrium” and some were monitored through time. Results indicated that tanδ was much more (×3) sensitive to EMC differences than E′/γ. R properties, especially tanδ R, were much more (×2–3) sensitive than L properties – resulting in strong increase of anisotropy with increasing EMC. In L direction, differences due to EMC remained moderate compared to the natural variability of wood for E′/γ, while for tanδ the EMC-induced changes were at least equal to natural variability in high-grade spruce. Vibrational properties did exhibit a hysteresis as a function of RH, but very little hysteresis as a function of EMC. The tanδ-EMC relation strongly depended on the actual time of stabilisation after reaching EMC. A related paper will address the transient, out of equilibrium effects of changing moisture conditions on the vibrational properties of wood.

Characterizing amplitude and frequency modulation cues in natural soundscapes: A pilot study on four habitats of a biosphere reserve.

Natural soundscapes correspond to the acoustical patterns produced by biological and geophysical sound sources at different spatial and temporal scales for a given habitat. This pilot study aims to characterize the temporal-modulation information available to humans when perceiving variations in soundscapes within and across natural habitats. This is addressed by processing soundscapes from a previous study [Krause, Gage, and Joo. (2011). Landscape Ecol. 26, 1247] via models of human auditory processing extracting modulation at the output of cochlear filters. The soundscapes represent combinations of elevation, animal, and vegetation diversity in four habitats of the biosphere reserve in the Sequoia National Park (Sierra Nevada, USA). Bayesian statistical analysis and support vector machine classifiers indicate that: (i) amplitude-modulation (AM) and frequency-modulation (FM) spectra distinguish the soundscapes associated with each habitat; and (ii) for each habitat, diurnal and seasonal variations are associated with salient changes in AM and FM cues at rates between about 1 and 100 Hz in the low (<0.5 kHz) and high (>1-3 kHz) audio-frequency range. Support vector machine classifications further indicate that soundscape variations can be classified accurately based on these perceptually inspired representations.

Design of Audio Signal Analyzer Based on MCU and FPGA

This audio signal analyzer is based on a microcontroller (MCU) and a field programmable gate array (FPGA). It consists of a controllable gain amplifier circuit, an active filter circuit, A / D conversion and D / A feedback circuits, and a main control circuit and liquid crystal display module. Through AD conversion, the audio signal is sampled, the continuous signal is discretized, and then the FFT fast Fourier transform operation is performed to analyze and process each frequency component and power of the audio signal in the time and frequency domain. By controlling the gain of the amplifier to expand the dynamic range of the input signal and improve the sensitivity, it can also complete the corresponding human-computer interaction control based on the PS2 keyboard input, while using the high-resolution LCD to display the signal spectrum. The audio signal frequency range that this system can accurately measure is 20Hz-10KHz, its amplitude range is 5mVpp-5Vpp, and the resolution is divided into 20Hz and 100Hz. The measured power accuracy is as high as 1%, and the period of the periodic signal can be accurately measured, which is the ideal solution for audio signal analyzers.

A Simple Methodology to Develop Bifilar, Quadrifilar, and Octofilar Calculable Resistors

This paper describes the development of bifilar, quadrifilar, and octofilar Calculable Resistors (CRs). The research involves Evanohm-S and Isaohm wire heat treatment processes to achieve temperature coefficients less than 0.5 μ Ω / Ω / ∘ C in the CR’s wire resistance element, tests of different terminal–wire joining techniques, and construction aspects achieving a stability of less than 0.05 μ Ω / Ω /day. This kind of construction methodology has not been presented in detail in previous CR papers, and it is essential to accomplish the correct parameters of a CR. Without it, the development of a CR can take several months or even years. A comparison between CRs developed in this research and a CR from the Federal Institute of Metrology (METAS) in Switzerland was carried out. Measurement results between the 10 k Ω octofilar CR and the METAS 1 k Ω coaxial CR show an agreement better than 0.35 μ Ω / Ω through the audio-frequency range. Therefore, the octofilar CR can be used as an AC resistance reference with traceability to the quantum Hall resistance in DC.

Activation in human auditory cortex in relation to the loudness and unpleasantness of low-frequency and infrasound stimuli

Low frequency noise (LFS) and infrasound (IS) are controversially discussed as potential causes of annoyance and distress experienced by many people. However, the perception mechanisms for IS in the human auditory system are not completely understood yet. In the present study, sinusoids at 32 Hz (at the lower limit of melodic pitch for tonal stimulation), as well as 8 Hz (IS range) were presented to a group of 20 normal hearing subjects, using monaural stimulation via a loudspeaker sound source coupled to the ear canal by a long silicone rubber tube. Each participant attended two experimental sessions. In the first session, participants performed a categorical loudness scaling procedure as well as an unpleasantness rating task in a sound booth. In the second session, the loudness scaling procedure was repeated while brain activation was measured using functional magnetic resonance imaging (fMRI). Subsequently, activation data were collected for the respective stimuli presented at fixed levels adjusted to the individual loudness judgments. Silent trials were included as a baseline condition. Our results indicate that the brain regions involved in processing LFS and IS are similar to those for sounds in the typical audio frequency range, i.e., mainly primary and secondary auditory cortex (AC). In spite of large variation across listeners with respect to judgments of loudness and unpleasantness, neural correlates of these interindividual differences could not yet be identified. Still, for individual listeners, fMRI activation in the AC was more closely related to individual perception than to the physical stimulus level.

An accurate higher order plate theory for vibrations of cross-laminated timber panels

In this contribution, bending vibrations of cross-laminated timber (CLT) panels are addressed. The focus is on the low to mid audio frequency range in view of the sound radiation properties of CLT. To this end, a plate theory recently proposed by the authors is adapted by introducing a deformation ansatz for the transverse displacement and neglecting insignificant terms, yielding a theory with six degrees of freedom. From the governing equations of motion, dispersion relations for the propagation of bending wave are derived, which also allow to compute the natural frequencies and mode shapes of bounded plates. The weak formulation of the equations of motion is presented. The accuracy of the proposed theory is validated for a simply supported rectangular CLT panel for which an analytical solution is available. The results are compared with first order shear deformation theory, revealing the limitations of this simplified theory in the present context. Finally, finite element solutions for the rectangular plate with non-classical boundary conditions are presented, as well as incorporating a floating floor construction, underlining the importance of numerical solutions for the practical application of this plate theory.

Kaolinite under pressure at audio frequency range and its electrical features

ABSTRACT Electrical features of a humid kaolinite specimens was measured at various pressures and at various frequencies . Surface impedance is supposed on kaolinite particle surfaces (from humidity), chemical reaction and charge transport along surface hydroxyls of kaolinite edges besides the permanent negative charges. Classic mixture laws do not support the interpretation of electrical properties, especially, at high pressures. Accordingly, interpretation was made with percolation threshold theories. Pressure increase causes decrease in pore spaces and accordingly increases possible connections of pore distances filled with humidity to total pore spaces after applying pressure. With pressure increase, the pore voids between particles decrease and water conducting paths increase. Also, dielectric constant and conductance increase with increase of pressure. On the other hand, at a certain pressure, at low frequencies, a noticeable increase of capacitance with pressure increase, that tends to reach constant value, for relatively high pressures. The diffusion and interfacial mechanisms was suggested to interpret samples with increase of pressure and frequency. The latter mechanism acts simultaneously with surface chemical reaction mechanism (Debye behavior) to give a depressed arc (relaxation time distribution). Finally, the pressure and frequency are effective factors on electrical properties.

Realization with Fabrication of Double-Gate MOSFET Based Class-AB Amplifier

This research work designs the class-AB amplifier with the application of Double-Gate (DG) MOSFET, which provides insight on how the amplifier can be utilized, in accordance with its future design. Main consideration is the use of DG MOSFET in audio amplifier design, for its low power and low noise application, voltage regulation for high to low power, etc. The challenge of this design is an attempt to use the DG MOSFET as prominent component, to demonstrate it as a usable in common electronic applications. Model of class-AB amplifier using the DG MOSFET (for audio amplifier) has been designed, fabricated, and thereafter analysed with its frequency and power characteristics. This proposed design with 2 Wrms audio amplifier drives a nominal 8 Ω load by a 100 mVrms input signal, for the typical audio frequency range of 20 Hz – 20 kHz.

A psychoacoustical study to investigate the perceived unpleasantness of infrasound combined with audio-frequency sound

At many immission sites of infrasound (frequency f &lt; 20 Hz), humans are exposed to a mixture of infrasound and sound in the common audio-frequency range (audio sound, 20 Hz &lt; f &lt; 20 kHz). Therefore, the purpose of this study was to examine the auditory perception of infrasound and audio sound not only in isolation but also in combination. This laboratory study aims to investigate the perceived unpleasantness of infrasound (sinusoid at 12 Hz) and audio sound (sinusoid at 1000 Hz, pink-noise 250–4000 Hz), presented alone or in combination with each other. A pairwise comparison task and a rating task using a numerical scale were conducted with 19 normal hearing listeners. In addition, individual detection thresholds were determined for the infrasound stimulus. Combinations of infrasound and audio sound were rated as equally or more unpleasant than either sound presented alone. Inter-individual differences in unpleasantness ratings using the numerical scale were particularly high for stimuli containing infrasound. This can only in part be related to the large variability in infrasound thresholds. These findings suggest that simultaneous exposure to infrasound and audio sound can increase the perceived unpleasantness when both are presented at a sufficient level above the detection threshold.

Accurate Constant Phase Elements Dedicated for Audio Signal Processing

This review paper introduces real-valued two-terminal fully passive RC ladder structures of the so-called constant phase elements (CPEs). These lumped electronic circuits can be understood as two-terminal elements described by fractional-order (FO) dynamics, i.e., current–voltage relation described by non-integer-order integration or derivation. Since CPEs that behave almost ideally are still not available as off-the-shelf components, the correct behavior must be approximated in the frequency domain and is valid only in the predefined operational frequency interval. In this study, an audio frequency range starting with 20 Hz and ending with 20 kHz has been chosen. CPEs are designed and values tabularized for predefined phase shifts that are commonly used in practice. If constructed carefully, a maximum phase error less than 0.5° can be achieved. Several examples of direct utilization of designed CPEs in signal processing applications are provided.