Hervé Lissek

Body part-centered and full body-centered peripersonal space representations.

Dedicated neural systems represent the space surrounding the body, termed Peripersonal space (PPS), by integrating visual or auditory stimuli occurring near the body with somatosensory information. As a behavioral proxy to PPS, we measured participants’ reaction time to tactile stimulation while task-irrelevant auditory or visual stimuli were presented at different distances from their body. In 7 experiments we delineated the critical distance at which auditory or visual stimuli boosted tactile processing on the hand, face, and trunk as a proxy of the PPS extension. Three main findings were obtained. First, the size of PPS varied according to the stimulated body part, being progressively bigger for the hand, then face, and largest for the trunk. Second, while approaching stimuli always modulated tactile processing in a space-dependent manner, receding stimuli did so only for the hand. Finally, the extension of PPS around the hand and the face varied according to their relative positioning and stimuli congruency, whereas the trunk PPS was constant. These results suggest that at least three body-part specific PPS representations exist, differing in extension and directional tuning. These distinct PPS representations, however, are not fully independent from each other, but referenced to the common reference frame of the trunk.

Acoustic dispersive prism

The optical dispersive prism is a well-studied element, which allows separating white light into its constituent spectral colors, and stands in nature as water droplets. In analogy to this definition, the acoustic dispersive prism should be an acoustic device with capability of splitting a broadband acoustic wave into its constituent Fourier components. However, due to the acoustical nature of materials as well as the design and fabrication difficulties, there is neither any natural acoustic counterpart of the optical prism, nor any artificial design reported so far exhibiting an equivalent acoustic behaviour. Here, based on exotic properties of the acoustic transmission-line metamaterials and exploiting unique physical behaviour of acoustic leaky-wave radiation, we report the first acoustic dispersive prism, effective within the audible frequency range 800 Hz–1300 Hz. The dispersive nature, and consequently the frequency-dependent refractive index of the metamaterial are exploited to split the sound waves towards different and frequency-dependent directions. Meanwhile, the leaky-wave nature of the structure facilitates the sound wave radiation into the ambient medium.

Broadband Low-Frequency Electroacoustic Absorbers Through Hybrid Sensor-/Shunt-Based Impedance Control

This paper proposes a hybrid impedance control architecture for an electroacoustic absorber that combines an improved microphone-based feedforward control with a current-driven electrodynamic loudspeaker system. Feedforward control architecture enables stable control to be achieved, and current driving method discards the effect of the voice coil inductance. A method is given for designing the transfer function to be implemented in the controller, according to a target-specific acoustic impedance and mechanical parameters of the transducer. Numerical simulations present the expected acoustic performance, introducing global performance indicators such as the bandwidth of efficient absorption. Experimental assessments in a waveguide confirmed the accuracy of the model and the efficiency of the hybrid control technique for achieving broadband stable low-frequency electroacoustic absorbers. An application to damping of resonances in a duct is also presented, and the application to the modal equalization in actual listening rooms is finally discussed.

Exploiting the leaky-wave properties of transmission-line metamaterials for single-microphone direction finding

A transmission-line acoustic metamaterial is an engineered, periodic arrangement of relatively small unit-cells, the acoustic properties of which can be manipulated to achieve anomalous physical behaviours. These exotic properties open the door to practical applications, such as an acoustic leaky-wave antenna, through the implementation of radiating channels along the metamaterial. In the transmitting mode, such a leaky-wave antenna is capable of steering sound waves in frequency-dependent directions. Used in reverse, the antenna presents a well defined direction-frequency behaviour. In this paper, an acoustic leaky-wave structure is presented in the receiving mode. It is shown that it behaves as a sound source direction-finding device using only one sensor. After a general introduction of the acoustic leaky-wave antenna concept, its radiation pattern and radiation efficiency are expressed in closed form. Then, numerical simulations and experimental assessments of the proposed transmission-line based structure, implementing only one sensor at one termination, are presented. It is shown that such a structure is capable of finding the direction of an incoming sound wave, from backward to forward, based on received sound power spectra. This introduces the concept of sound source localization without resorting to beam-steering techniques based on multiple sensors.

Observation of Vehicle Axles Through Pass-by Noise: A Strategy of Microphone Array Design

This paper focuses on road traffic monitoring using sounds and proposes, more specifically, a microphone array design methodology for observing vehicle trajectory from acoustic-based correlation functions. In a former work, authors have shown that combining generalized cross correlation (GCC) functions and a particle filter onto the audio signals simultaneously acquired by two sensors placed near the road allows the joint estimation of the speed and the wheelbase length of road vehicles as they pass by. This is mainly due to the broadband nature of the tire/road noise, which makes their spatial dissociation possible by means of an appropriate GCC processor. At the time, nothing has been said about the best distance to chose between the sensors. A methodology is proposed here to find this optimum, which is expected to improve the observation quality and, thus, the tracking performance. Theoretical developments of this paper are partially assessed with preliminary experiments.

Obtaining Binaural Room Impulse Responses From B-Format Impulse Responses Using Frequency-Dependent Coherence Matching

Measuring binaural room impulse responses (BRIRs) for different rooms and different persons is a costly and time-consuming task. In this paper, we propose a method that allows to compute BRIRs from a B-format room impulse response (B-format RIR) and a set of head-related transfer functions (HRTFs). This enables to measure the room-related properties and head-related properties of BRIRs separately, reducing the amount of measurements necessary for obtaining BRIRs for different rooms and different persons to one B-format RIR measurement per room and one HRTF set per person. The BRIRs are modeled by applying an HRTF to the direct sound part of the B-format RIR and using a linear combination of the reflections part of the B-format RIR. The linear combination is determined such that the spectral and frequency-dependent interaural coherence cues match those of corresponding directly measured BRIRs. A subjective test indicates that the computed BRIRs are perceptually very similar to corresponding directly measured BRIRs.

Sensorless electroacoustic absorbers through synthesized impedance control for damping low-frequency modes in cavities

This paper presents a concept of sensorless electroacoustic absorber for damping the low-frequency modes in a cavity such as a duct or a room. Taking advantage of the reciprocity of the voice coil transducer, it is shown that a synthetic electrical admittance can be designed so that the loudspeaker diaphragm is matched to a target specific acoustic impedance. This electroacoustic device provides a relatively broadband sound absorption that can be used to dampen room modes regardless of the sound field in which the loudspeaker is located. A digital filter is used to replicate the frequency response of the synthetic load, and a voltage-controlled current source is needed so that the filter is seen as an electrical admittance. Unlike previous attempts to implement the synthetic load using an electrical network, greater flexibility and accuracy can be obtained. Experimental results confirmed the validity of this sensorless electroacoustic absorber (SEA) in a 1D sound field, showing that the dynamic range of the sound pressure level in a duct can be reduced by 15 dB from 50 Hz to 300 Hz compared to a hard surface panel. A discussion on the strengths and limitations of this concept is provided, in particular with a view to employing SEAs for modal equalization in actual listening rooms.

Optimization of electroacoustic resonators for semi-active room equalization in the low-frequency range

At low frequencies, standing waves within the room cause large frequency-response variations in the listening environment, such as audio rooms or recording studios. This unwanted phenomenon has a significant impact on the sound quality of an audio system. Unfortunately, state-of-the-art soundproofing solutions cannot efficiently handle such low-frequency sound energy. To alleviate this problem, electroacoustic resonators can be used to damp room modes. This concept is based on the connection of direct-radiator loudspeakers to synthetic electrical loads allowing the passive dissipation of a certain part of the incoming acoustic energy of the sound field. Through judicious control of acoustic impedance depending of the placement of the electroacoustic resonators in the room, a significant damping of the dominant natural resonances can be achieved in order to meet the specifications of audio reproduction. This paper investigates the optimization and the spatial arrangement of electroacoustic resonators with a view to damp the low-frequency acoustic resonances in enclosed spaces.

From the electrical shunting of a loudspeaker to active impedance control

Variable acoustic properties can be obtained on an electroacoustic transducer’s voicing face by very basic control strategies, among which are the shunting of the loudspeaker (shortcut, variable electric load, or negative resistance disposals). It is proven that enhanced controllability and better performances can be obtained by way of hybrid feedback control, consisting in a double feedback loop, one on acoustic pressure at the diaphragm and the other on its velocity, leading to a global acoustic impedance control. The present work will describe the theory of the hybrid feedback control, by way of block diagrams aiming at visualizing the control principle, starting from the shunted loudspeaker. Simulations of performances obtained on Matlab/Simulink will then be presented, and compared to experimental results obtained on analog prototypes mounted at the end of a dedicated impedance tube. A discussion on stability will then follow, leading to concluding remarks on the disposal behavior and possible means of enhancements.

Localization of Sound Sources in a Room with One Microphone

Estimation of the location of sound sources is usually done using microphone arrays. Such settings provide an environment where we know the difference between the received signals among different microphones in the terms of phase or attenuation, which enables localization of the sound sources. In our solution we exploit the properties of the room transfer function in order to localize a sound source inside a room with only one microphone. The shape of the room and the position of the microphone are assumed to be known. The design guidelines and limitations of the sensing matrix are given. Implementation is based on the sparsity in the terms of voxels in a room that are occupied by a source. What is especially interesting about our solution is that we provide localization of the sound sources not only in the horizontal plane, but in the terms of the 3D coordinates inside the room.