Audio Frequency Band Research Articles

Improved tactile speech perception and noise robustness using audio-to-tactile sensory substitution with amplitude envelope expansion

Recent advances in haptic technology could allow haptic hearing aids, which convert audio to tactile stimulation, to become viable for supporting people with hearing loss. A tactile vocoder strategy for audio-to-tactile conversion, which exploits these advances, has recently shown significant promise. In this strategy, the amplitude envelope is extracted from several audio frequency bands and used to modulate the amplitude of a set of vibro-tactile tones. The vocoder strategy allows good consonant discrimination, but vowel discrimination is poor and the strategy is susceptible to background noise. In the current study, we assessed whether multi-band amplitude envelope expansion can effectively enhance critical vowel features, such as formants, and improve speech extraction from noise. In 32 participants with normal touch perception, tactile-only phoneme discrimination with and without envelope expansion was assessed both in quiet and in background noise. Envelope expansion improved performance in quiet by 10.3% for vowels and by 5.9% for consonants. In noise, envelope expansion improved overall phoneme discrimination by 9.6%, with no difference in benefit between consonants and vowels. The tactile vocoder with envelope expansion can be deployed in real-time on a compact device and could substantially improve clinical outcomes for a new generation of haptic hearing aids.

Acoustical Analysis of Insertion Losses of Ceiling Materials

This study concentrates on measuring, analyzing and recommending the ceiling materials most suited for the reduction of distinct frequency noise levels with focus on rain noise. A frequency analyzer has been used to measure and obtained accurate sound level (LP) data of the rain noise outside, and inside five buildings with diverse acoustical ceiling materials in South Eastern Nigeria. It was done with and without the ceiling partition (or noise barrier) for the audio and narrow frequency band without contribution from other outdoor-related noise sources. Insertion losses of the ceiling materials were calculated using the data obtained from the measured LP. Result obtained from the analysis indicated that the ceiling material found to effectively reduce the noise levels from external noise source. The type for speech reception threshold frequencies of more than 125 Hz and higher audiometric range was moabi wood with peak LP of 21.20 dB at 500 Hz. While for lower frequencies where the ears are least responsive was plaster of Paris (POP) with peak LP of 12.61 dB at 62.5 Hz. This makes “moabi wood” most suitable in lecture rooms, conference halls and large auditoriums as ceiling material, in consideration of its capability to provide notable attenuation of rain noise within the building. This is in accordance with several other studies done on this subject. In general, at much low frequencies and frequencies greater than 2k Hz significant reduction in the rain noise level was observed.

Improving speech perception for hearing-impaired listeners using audio-to-tactile sensory substitution with multiple frequency channels

Cochlear implants (CIs) have revolutionised treatment of hearing loss, but large populations globally cannot access them either because of disorders that prevent implantation or because they are expensive and require specialist surgery. Recent technology developments mean that haptic aids, which transmit speech through vibration, could offer a viable low-cost, non-invasive alternative. One important development is that compact haptic actuators can now deliver intense stimulation across multiple frequencies. We explored whether these multiple frequency channels can transfer spectral information to improve tactile phoneme discrimination. To convert audio to vibration, the speech amplitude envelope was extracted from one or more audio frequency bands and used to amplitude modulate one or more vibro-tactile tones delivered to a single-site on the wrist. In 26 participants with normal touch sensitivity, tactile-only phoneme discrimination was assessed with one, four, or eight frequency bands. Compared to one frequency band, performance improved by 5.9% with four frequency bands and by 8.4% with eight frequency bands. The multi-band signal-processing approach can be implemented in real-time on a compact device, and the vibro-tactile tones can be reproduced by the latest compact, low-powered actuators. This approach could therefore readily be implemented in a low-cost haptic hearing aid to deliver real-world benefits.

Skin tissue perfusion mapping triggered by an audio-(de)modulated reference signal.

Spatial mapping of skin perfusion provides essential information about physiological processes that are often hidden from the eyes of the examining physician. The perfusion map quality depends on several key factors, such as the camera system type, frame rate, sensitivity, or signal-to-noise ratio. When investigating physiological parameters, the reference signal allows for increasing the spatial resolution of the photoplethysmography imaging (PPGI) system. On the other hand, it increases the system complexity and the synchronization prerequisites. Our solution is a hardware device that modulates the reference biosignal into the audio frequency band. This signal is connected to the mic input of a digital camera or a smartphone, enabling the transformation of such a device into a PPGI measurement system even in the case of compressed video recording using lock-in amplification technique. It also brings the possibility of synchronous recording of PPGI and another reference signal such as conventional photoplethysmogram or electrocardiogram.

Acoustic and vibration isolation for a gravity gradiometer.

Vibration in the audio frequency band affects the performance of rotating gravity gradiometers used for airborne mineral exploration. This is probably due to translation to rotation coupling inside the gradiometer platform. It was found that the DC gravity gradient signal was proportional to the square of the third time derivative of position, or jerk squared. The demanding airborne environment for such instrumentation demands a light weight broadband acoustic shield and vibration isolator. This paper presents the design principles for such an isolator, based on vibration isolated spherical shell structures. Performance data are presented as well as flight test data that demonstrated a 14% gravity gradient noise reduction compared with an unshielded instrument.

Experimental Research on the Noise Characteristics of the Output Field of the Optical Filter Cavity

Precision measurement is an important direction of today's frontier scientific research. Using lasers to achieve high-precision target measurement has become an important way to improve measurement accuracy, which can be applied in various fields. However, for a certain application, the measurement accuracy will directly depend on the noise level of the laser source. Most applications require that the measurement frequency band is concentrated in the audio frequency band. In order to obtain a low-noise laser source with shot noise limited in the applied frequency band, active and/or passive noise reduction are the usual choice, i.e., active feedback control and filter cavity technique, and so on. Therefore, noise analysis and suppression techniques are the main concern of the precision measurement. The optical filter cavity acts as an optical low-pass filter, which can effectively suppress high-frequency noise beyond its linewidth. In this work, we found that the intensity noise of the output field of an optical filter cavity is higher than the noise floor of the laser. The main sources of noise are analyzed through experiments:(1) excess noise introduced by cavity length locking; (2) laser phase and pointing noises coupled to the intensity one by the cavity. To cancel the excess noise as much as possible, we optimize the feedback control loop by measuring the open-loop and closed-loop transfer functions of the MC, combined with the critical proportionality method. All the control loop are homemade, and the PID is designed with a FPGA board for expediently achieving a noise reduction up to 30 dB at the audio frequency. Then the control loop is optimized as the best condition without introducing the excess noise. Compared with the free-running laser, MC filters out the high-frequency noise, meanwhile converts the phase noise and pointing noise of input field into the intensity noise of the output field. Therefore, the power noise spectrum in the audio segment is still higher than that of the input optical field itself. In the future, an active control loop will be applied to suppress the noise power. The experimental results provide the basic means for applied research such as feedback control loop noise analysis, which will promote the development of precision measurement to higher measurement accuracy.

Experimental study on noise characteristics of audio frequency band in output field of optical filter cavity

Precision measurement is an important direction of today’s frontier scientific research. Using lasers to achieve high-precision target measurement has become an important way to improve measurement accuracy, which can be used in various fields. However, for a certain application, the measurement accuracy will directly depend on the noise level of the laser source. Most of applications require that the measurement frequency band is concentrated in the audio frequency band. In order to obtain a low-noise laser source with shot noise limited in the applied frequency band, active and/or passive noise reduction is usually an option, i.e. active feedback control or filter cavity technique, etc. Therefore, noise analysis and suppression techniques are the main concern of the precision measurement. The optical filter cavity acts as an optical low-pass filter, which can effectively suppress high-frequency noise beyond its linewidth. In this work, we find that the intensity noise of the output field of an optical filter cavity is higher than the noise floor of the laser. The main sources of noise are analyzed experimentally, showing that 1) excess noise is introduced by cavity length locking, and 2) laser phase and pointing noises are coupled to the intensity one by the cavity. To cancel the excess noise as much as possible, we optimize the feedback control loop by measuring the open-loop and closed-loop transfer functions of the mode cleaner (MC), combined with the critical proportionality method. All the control loops are homemade, and the proportional-integral-derivative (PID) is designed with a field programmable gate array board for expediently achieving a noise reduction up to 30 dB at the audio frequency. Then the control loop is optimized to the best condition without introducing the excess noise. Compared with the free-running laser, MC filters out the high-frequency noise, meanwhile converts the phase noise and pointing noise of input field into the intensity noise of the output field. Therefore, the power noise spectrum in the audio band is still higher than that of the input optical field itself. In the future, an active control loop will be used to suppress the noise power. The experimental results provide the basic means for application research such as feedback control loop noise analysis, which will promote the development of precision measurement toward higher measurement accuracy.

Comb-partitioned frequency-domain constraint adaptive algorithm for active noise control

Active noise control (ANC) is gaining credence as an effective approach in mitigating low-frequency urban noise. Current ANC algorithms that attenuate noise across the full audio frequency band, often exert control effort excessively at higher frequencies. Moreover, such unrestrained control unavoidably attenuates some critical sounds, such as alarms and warning signals. In practice, excessive control effort in ANC usually results in output-saturation distortion, which affects the adaptive system stability and degrades the residual audio quality. To provide greater flexibility of control in frequency bands of interest without incurring output saturation, this paper proposes two variants of the filtered reference comb-partitioned frequency-domain adaptive filter (FxCFDAF) algorithm, namely the leaky FxCFDAF and drop-out FxCFDAF algorithms, which exert output-effort constraint at the control filter in the frequency domain. In addition, the comb-partitioning approach in the proposed FxCFDAF algorithms is delayless and computationally-efficient, which are essential for practical implementation, unlike the conventional frequency-domain adaptive algorithm. Experimental simulations carried out on measured primary and secondary paths validate the proposed algorithms’ advantage over the conventional FxLMS algorithm in mitigating large-amplitude noise without output saturation.

Automated source of squeezed vacuum states driven by finite state machine based software.

In the last few decades, much effort has been made for the production of squeezed vacuum states in order to reduce quantum noise in the audio-frequency band. This technique has been implemented in all running gravitational-wave interferometric detectors and helped to improve their sensitivity. While the detectors are acquiring data for astrophysical observations, they must be kept in the operating condition, also called "science mode," that is, a state that requires the highest possible duty-cycle for all the instrumental parts and controls. We report the development of a highly automated setup for the generation of optical squeezed states, where all the required control loops are supervised by a software based on finite state machines; we took special care to grant ease of use, stability of operation, and possibility of auto-recovery. Moreover, the setup has been designed to be compatible with the existing software and hardware infrastructure of the Virgo detector. In this paper, we discuss the optical properties of this squeezing setup, the locking techniques, and the automation algorithms.

High-yield, wafer-scale fabrication of ultralow-loss, dispersion-engineered silicon nitride photonic circuits

Low-loss photonic integrated circuits and microresonators have enabled a wide range of applications, such as narrow-linewidth lasers and chip-scale frequency combs. To translate these into a widespread technology, attaining ultralow optical losses with established foundry manufacturing is critical. Recent advances in integrated Si3N4 photonics have shown that ultralow-loss, dispersion-engineered microresonators with quality factors Q > 10 × 106 can be attained at die-level throughput. Yet, current fabrication techniques do not have sufficiently high yield and performance for existing and emerging applications, such as integrated travelling-wave parametric amplifiers that require meter-long photonic circuits. Here we demonstrate a fabrication technology that meets all requirements on wafer-level yield, performance and length scale. Photonic microresonators with a mean Q factor exceeding 30 × 106, corresponding to 1.0 dB m−1 optical loss, are obtained over full 4-inch wafers, as determined from a statistical analysis of tens of thousands of optical resonances, and confirmed via cavity ringdown with 19 ns photon storage time. The process operates over large areas with high yield, enabling 1-meter-long spiral waveguides with 2.4 dB m−1 loss in dies of only 5 × 5 mm2 size. Using a response measurement self-calibrated via the Kerr nonlinearity, we reveal that the intrinsic absorption-limited Q factor of our Si3N4 microresonators can exceed 2 × 108. This absorption loss is sufficiently low such that the Kerr nonlinearity dominates the microresonator’s response even in the audio frequency band. Transferring this Si3N4 technology to commercial foundries can significantly improve the performance and capabilities of integrated photonics.

Customised enriched acoustic environment for sound therapy of tinnitus

Tinnitus is an auditory disorder very difficult to treat. Whereas up until now there is not a “cure” for tinnitus, the most extended treatment combines counselling with sound therapy. When this sound is a broadband noise in the audio frequency band, this protocol is named tinnitus retraining therapy. Even though broadband noise was proposed at the beginning as the stimulus for sound therapy, many other sounds have been subsequently proposed and used, including tones, noise bands, music, and nature sounds. Although any sound, low enough to avoid annoyance, discomfort or hearing damage, is better than silence for tinnitus treatment, it is not still clear the relationship of the success of the therapy with the properties of the sound stimuli. The aim of this article is to propose an optimal sound treatment that provides a precise and selective stimulation of the whole auditory system. The proposed sound stimulus, Enriched Acoustic Environment, consists of sequential tones or broadband noise matched to the HL curves of the patients. The acoustical characteristics of these stimuli are analyzed and their positive effects in the treatment of subjects with tinnitus are reported.

Dissipative Quantum Sensing with a Magnetometer Based on Nitrogen-Vacancy Centers in Diamond

Quantum sensing uses quantum systems as sensors to capture weak signals and is providing opportunities in science and technology. The biggest challenge in quantum sensing is decoherence due to the coupling between the sensor and the environment. The dissipation will destroy the quantum coherence and reduce the performance of the sensor. Here we show that quantum sensing can be realized under dissipation by engineering the steady state of the sensor. We demonstrate this protocol with a magnetometer based on ensemble nitrogen-vacancy centers in diamond, while neither high-quality initialization or readout of the sensor nor sophisticated dynamical decoupling sequences are required. Thus our method provides a concise and decoherence-resistant means of quantum sensing. The frequency resolution and precision of our magnetometer are far beyond the coherence time of the sensor. Furthermore, we show that the dissipation can be engineered to improve the performance of our sensor. By increasing the laser pumping, magnetic signals in a broad audio-frequency band from dc up to 140 kHz can be tackled by our method. Besides the potential applications in magnetic sensing and imaging on the microscopic scale, our results may provide opportunities for improvement of a variety of high-precision spectroscopies based on other quantum sensors.

Room-temperature optomechanical squeezing

One of the noise sources that currently limits gravitational wave (GW) detectors comes from the quantum nature of the light causing uncertain amplitude and phase. Phase uncertainty limits the precision of an interferometric measurement. This measurement is also subject to quantum back-action, caused by the radiation pressure force fluctuations produced by the amplitude uncertainty (QRPN). In order to lower this quantum noise, GW detectors plan to use squeezed light injection. In this thesis, I focus on using radiation-pressure-mediated optomechanical (OM) interaction to generate squeezed light. Creating squeezed states by using OM interaction enables wavelength-independent squeezed light sources that may also be more compact and robust than traditionally used non-linear crystals. We analyze the system with realistic imperfections (losses & classical noise), and use the concepts to design an experiment to obtain the most possible squeezing in a broad audio-frequency band at room temperature. This involves an optimization for the optical properties of the cavity and the mechanical properties of the oscillator. We then show its experimental implementation, and subsequent observation of QRPN as well as OM squeezing. These are the first ever direct observations of a room temperature oscillator's motion being overwhelmed by vacuum fluctuations. This is shown in the low frequency band, which is relevant to GW detectors, but poses its own technical challenges, and hence has not been done before. Being in the back-action dominated regime along with optimized optical properties has also enabled us to observe OM squeezing. That is the first direct observation of quantum noise suppression in a room temperature OM system. It is also the first direct evidence of quantum correlations in the audio frequency band, in a broad band at non-resonant frequencies.

A low-noise, high-SNR balanced homodyne detector for the bright squeezed state measurement in 1–100 kHz range**Project supported by the National Natural Science Foundation of China (Grant Nos. 11654002, 61575114, 11874250, and 11804207), the National Key Research and Development Program of China (Grant No. 2016YFA0301401), the Program for Sanjin Scholar of Shanxi Province, China, the Program for Outstanding Innovative Teams of

We report a low-noise, high-signal-to-noise-ratio (SNR) balanced homodyne detector based on the standard transimpedance amplifier circuit and the inductance and capacitance combination for the measurement of the bright squeezed state in the range from 1 kHz to 100 kHz. A capacitance is mounted at the input end of the AC branch to prevent the DC photocurrent from entering the AC branch and avoid AC branch saturation. By adding a switch at the DC branch, the DC branch can be flexibly turned on and off on different occasions. When the switch is on, the DC output provides a monitor signal for laser beam alignment. When the switch is off, the electronic noise of the AC branch is greatly reduced at audio-frequency band due to immunity to the impedance of the DC branch, hence the SNR of the AC branch is significantly improved. As a result, the electronic noise of the AC branch is close to −125 dBm, and the maximum SNR of the AC branch is 48 dB with the incident power of 8 mW in the range from 1 kHz to 100 kHz. The developed photodetector paves a path for measuring the bright squeezed state at audio-frequency band.

자동차 연료 펌프용 BLDC 모터의 전자기적인 소음 저감에 관한 연구

This paper proposes a driving method in order to reduce the electromagnetic noise of blushless DC motor for fuel pump of vehicles. In recent years, these motors have been widely employed in the electric fuel pumps because of its high-efficiency, high-reliability, compact size, light weight, and simple control method. However, despite the various advantages, brushless DC motors have realistic problems. These problems are acoustic noise and vibration, which are caused by torque ripple and sudden current fluctuation in the stator windings due to the mechanical structures and control methods. If the mechanical structures are redesigned or the control methods are improved, both cogging torque and torque ripple due to commutation can be reduced. Nevertheless, if quasi-square-wave currents are supplied to these motors by conventional methods, the stator windings may generate the electromagnetic noise and vibration within the audio frequency bands. In this paper, a sinusoidal-wave driving method is proposed to suppress the fluctuating currents. The reduction effects on noise and vibration are verified through computer simulations and experiments.

Observation of Squeezed Light in the 2 μm Region.

We present the generation and detection of squeezed light in the 2 μm wavelength region. This experiment is a crucial step in realizing the quantum noise reduction techniques that will be required for future generations of gravitational-wave detectors. Squeezed vacuum is generated via degenerate optical parametric oscillation from a periodically poled potassium titanyl phosphate crystal, in a dual resonant cavity. The experiment uses a frequency stabilized 1984nm thulium fiber laser, and squeezing is detected using balanced homodyne detection with extended InGaAs photodiodes. We have measured 4.0±0.1 dB of squeezing and 10.5±0.5 dB of antisqueezing relative to the shot noise level in the audio frequency band, limited by photodiode quantum efficiency. The inferred squeezing level directly after the optical parametric oscillator, after accounting for known losses and phase noise, is 10.7dB.

Proposal of the pipe diagnosis method using in-plane bending vibration of cylindrical shell

In this paper, deterioration diagnosis for distribution main pipe was studied using the uniform cylindrical shell approximation and in-plane bending mode. The in-plane bending mode is expected to have high accuracy in detection of deterioration, because the eigen frecuency of the mode is proportional to pipe thickness. First, using the finite element method, the characteristics of in-plane bending mode are investigated. It is confirmed that in-plane bending mode has little small dependence on the pipe length and the boundary conditions at the pipe ends, it appears in the audio frequency bands, and it has linear dependence on the pipe thickness. In addition, formula with two dimensional ring approximation is derived. Moreover, the average thickness and the uniform-cylindrical shell approximation are introduced for deal with the deteriorated pipe. Using the thinning pipe thickness of previous study, validity of the average thickness and the uniform-cylindrical shell approximation were confirmed. On the other hand, actual pipeline has the sub-structure, for example, valve, hydrant, and so on. In order to deal with the coupled vibration between the cylindrical shell and the sub-structure, eigenvalue analysis are conducted using the Semi-Analytical Receptance Method (SARM). The experimental consideration were conducted in case of that the sub-structure non-attached case. The in-plane bending mode is observed experimentally on the actual pipe system and its resonant frequency shows good match with the theoretical values.

Generation of squeezed states at low analysis frequencies

Squeezed states are important sources in quantum physics, which have potential applications in fields such as quantum teleportation, quantum information networks, quantum memory, and quantum metrology and precise measurements. For our interest, the squeezed vacuum will be used in the quantum-enhanced optical atomic magnetometers, filling the vacuum port of the probe beam to improve measurement sensitivity. Based on the sub-threshold optical parametric oscillator (OPO) with PPKTP crystal, the squeezed vacuum at rubidium D1 line of 795 nm is obtained. In our work, we investigate the noise sources in an OPO system. By carefully controlling the classical noise source, the squeezing band extends to the analysis frequency of 2.6 kHz. The flat squeezing trace is 2.8 dB below the shot noise limit. In our work, we focus on the difference between the squeezing results at the analysis frequency of kilohertz regime at two different wavelengths, 1064 nm and 795 nm. The difference mainly comes from the absorption of 795 nm laser and its second harmonic at 397.5 nm in crystal (397.5 nm laser is at the edge of transparent window of PPKTP crystal that has an absorption index much higher than at other wavelength). The absorption induced nonlinear loss and thermal instability greatly affect the squeezing results, which is discussed in our work. Squeezing level at 795 nm is worse than at 1064 nm due to the above-mentioned factors. Noise coupling to the detection system limits the squeezing band. In the audio frequency band, squeezing is easily submerged in roll-up noises and the measured squeezing level is limited. Two factors limit the obtained squeezing:the technical noise induced in the detection and the squeezing degradation by the noise coupling of the control beams. In experiment, we carefully control the classical noise at analytical frequency of kilohertz by means of a vacuum-injected OPO, a counter-propagating cavity locking beam with orthogonal polarization, low noise homodyne detector, stable experimental system and quantum noise locking method for squeezing phase locking. Firstly, to preclude the classical noise from coupling the laser source, we use the vacuum injected OPO. A signal beam helps optimize the parametric gain and is blocked in the squeezing measurement process. In order to maintain the OPO, a counter-propagating beam with orthogonal polarization is used for locking the cavity. Then, a low noise balanced homodyne detector with a common-mode rejection ratio of 45 dB helps improve the audio frequency detection. Finally, the quantum noise locking provides a method to lock the relative phase between the coherent beam and the squeezed vacuum field. With the combination of these technical improvements, a squeezed vacuum of 2.8 dB is obtained at the analysis frequency of 2.6-100 kHz. The obtained squeezing level is mainly limited by the relatively large loss in OPO, which is induced by ultra-violet absorption in PPKTP crystal. The generated squeezed field is used to reduce the polarization noise of probe beam in an optical magnetometer, in order to increase detection sensitivity.

Polarization squeezing at the audio frequency band for the Rubidium D1 line.

A 2.8-dB polarization squeezing of the Stokes operatorS^2for the rubidium D1 line (795 nm) is achieved, with the lowest squeezing band at an audio frequency of 2.6 kHz. It is synthetized by a bright coherent beam and a squeezed vacuum, which are orthogonally polarized and share same frequency. Two methods are applied to support the optical parametric oscillator: an orthogonally-polarized locking beam that precludes residual unwanted interference and quantum noise locking method that locks the squeezing phase. Besides, the usage of low noise balanced detector, mode cleaner and the optical isolator helped to improve the audio frequency detection. The squeezing level is limited by absorption-induced losses at short wavelengths, which is 397.5 nm. The generated polarization squeezed light can be used in a quantum enhanced magnetometer to increase the measurement sensitivity.

Effect of Keysight 3458A Jitter on Precision of Phase Difference Measurement

A new method improving precision of the phase difference measurement performed by two Keysight 3458A multimeters is proposed. The method is based on external synchronization of the multimeters by a specially selected sampling interval reducing the effect of the finite resolution of an internal time base (jitter) on the performance of the multimeters. By using this method, precision of the phase difference estimation in the audio frequency band can significantly be improved as compared with the commonly used synchronization schemes.