Unidirectional amplification with acoustic non-Hermitian space−time varying metamaterial

Space−time modulated metamaterials support extraordinary rich applications, such as parametric amplification, frequency conversion, and non-reciprocal transmission. The non-Hermitian space−time varying systems combining non-Hermiticity and space−time varying capability, have been proposed to realize wave control like unidirectional amplification, while its experimental realization still remains a challenge. Here, based on metamaterials with software-defined impulse responses, we experimentally demonstrate non-Hermitian space−time varying metamaterials in which the material gain and loss can be dynamically controlled and balanced in the time domain instead of spatial domain, allowing us to suppress scattering at the incident frequency and to increase the efficiency of frequency conversion at the same time. An additional modulation phase delay between different meta-atoms results in unidirectional amplification in frequency conversion. The realization of non-Hermitian space−time varying metamaterials will offer further opportunities in studying non-Hermitian topological physics in dynamic and nonreciprocal systems.

Auditory model-based estimation of the effect of head-worn devices on frontal horizontal localisation

Auditory localisation accuracy may be degraded when a head-worn device (HWD), such as a helmet or hearing protector, is used. A computational method is proposed in this study for estimating how horizontal plane localisation is impaired by a HWD through distortions of interaural cues. Head-related impulse responses (HRIRs) of different HWDs were measured with a KEMAR and a binaural auditory model was used to compute interaural cues from HRIR-convolved noise bursts. A shallow neural network (NN) was trained with data from a subjective listening experiment, where horizontal plane localisation was assessed while wearing different HWDs. Interaural cues were used as features to estimate perceived direction and position uncertainty (standard deviation) of a sound source in the horizontal plane with the NN. The NN predicted the position uncertainty of localisation among subjects for a given HWD with an average estimation error of 1°. The obtained results suggest that it is possible to predict the degradation of localisation ability for specific HWDs in the frontal horizontal plane using the method.

Cardiorespiratory kinetics in exercise physiology: estimates and predictions using randomized changes in work rate

Purpose Kinetics of cardiorespiratory parameters (CRP) in response to work rate (WR) changes are evaluated by pseudo-random binary sequences (PRBS testing). In this study, two algorithms were applied to convert responses from PRBS testing into appropriate impulse responses to predict steady states values and responses to incremental increases in exercise intensity. Methods 13 individuals (age: 41 ± 9 years, BMI: 23.8 ± 3.7 kg m−2), completing an exercise test protocol, comprising a section of randomized changes of 30 W and 80 W (PRBS), two phases of constant WR at 30 W and 80 W and incremental WR until subjective fatigue, were included in the analysis. Ventilation ($$\dot{V}_{{\text{E}}}$$ V ˙ E ), O2 uptake ($$\dot{V}{\text{O}}_{2}$$ V ˙ O 2 ), CO2 output ($$\dot{V}{\text{CO}}_{2}$$ V ˙ CO 2 ) and heart rate (HR) were monitored. Impulse responses were calculated in the time domain and in the frequency domain from the cross-correlations of WR and the respective CRP. Results The algorithm in the time domain allows better prediction for $$\dot{V}{\text{O}}_{2}$$ V ˙ O 2 and $$\dot{V}{\text{CO}}_{2}$$ V ˙ CO 2 , whereas for $$\dot{V}_{{\text{E}}}$$ V ˙ E and HR the results were similar for both algorithms. Best predictions were found for $$\dot{V}{\text{O}}_{2}$$ V ˙ O 2 and HR with higher (3–4%) 30 W steady states and lower (1–4%) values for 80 W. Tendencies were found in the residuals between predicted and measured data. Conclusion The CRP kinetics, resulting from PRBS testing, are qualified to assess steady states within the applied WR range. Below the ventilatory threshold, $$\dot{V}{\text{O}}_{2}$$ V ˙ O 2 and HR responses to incrementally increasing exercise intensities can be sufficiently predicted.

The impulse response of optic flow-sensitive descending neurons to roll m-sequences

ABSTRACT When animals move through the world, their own movements generate widefield optic flow across their eyes. In insects, such widefield motion is encoded by optic lobe neurons. These lobula plate tangential cells (LPTCs) synapse with optic flow-sensitive descending neurons, which in turn project to areas that control neck, wing and leg movements. As the descending neurons play a role in sensorimotor transformation, it is important to understand their spatio-temporal response properties. Recent work shows that a relatively fast and efficient way to quantify such response properties is to use m-sequences or other white noise techniques. Therefore, here we used m-sequences to quantify the impulse responses of optic flow-sensitive descending neurons in male Eristalis tenax hoverflies. We focused on roll impulse responses as hoverflies perform exquisite head roll stabilizing reflexes, and the descending neurons respond particularly well to roll. We found that the roll impulse responses were fast, peaking after 16.5–18.0 ms. This is similar to the impulse response time to peak (18.3 ms) to widefield horizontal motion recorded in hoverfly LPTCs. We found that the roll impulse response amplitude scaled with the size of the stimulus impulse, and that its shape could be affected by the addition of constant velocity roll or lift. For example, the roll impulse response became faster and stronger with the addition of excitatory stimuli, and vice versa. We also found that the roll impulse response had a long return to baseline, which was significantly and substantially reduced by the addition of either roll or lift.

dEchorate: a calibrated room impulse response dataset for echo-aware signal processing

This paper presents a new dataset of measured multichannel room impulse responses (RIRs) named dEchorate. It includes annotations of early echo timings and 3D positions of microphones, real sources, and image sources under different wall configurations in a cuboid room. These data provide a tool for benchmarking recent methods in echo-aware speech enhancement, room geometry estimation, RIR estimation, acoustic echo retrieval, microphone calibration, echo labeling, and reflector position estimation. The dataset is provided with software utilities to easily access, manipulate, and visualize the data as well as baseline methods for echo-related tasks.

Acoustic Room Impulse Response Shaping

<p>Impulse response shaping is a technique for modifying the characteristics of a linear channel to achieve desirable characteristics. The technique is well-known in the field of wireless communication. Acoustic impulse response shaping is used to reduce the effects of reverberation on audio signals propagating inside a room and is thus used for listening room compensation. This thesis addresses innovative approaches for acoustic impulse response shaping. Many techniques have been proposed in the literature for canceling or reducing the effect of reverberation on the audio signal. Impulse response inversion attempts to completely cancel the effect of reverberations whereas impulse response shortening (or shaping) only partly equalizes the room impulse responses. Shortening has less stringent constraints than inversion and this can result in more robust solutions and thus more practically realizable systems. Acoustic impulse response shaping works on measured room impulse responses and designs pre-filters to be placed before the loudspeakers so that the reverberation is reduced at the listening positions. When sampled, the room responses typically contain thousands or tens of thousands (N ) of samples. Thus, the shaping algorithm needs to be computationally fast and memory efficient in order to implement the system in real time. The techniques presented in the literature use interior point methods or steepest descent algorithms, which are computationally slow or require memory of the order of N² . This thesis presents shaping approaches based on the Dual Augmented Lagrangian Method (DALM), known in the literature on sparse reconstruction for its super-linear convergence. The method presented here also makes use of the concept of a Forward Adjoint Oracle (FAO) to make the shaping algorithm memory efficient. Thus, the thesis presents computationally fast and memory efficient shaping algorithms that can be used for practically realizable systems. The thesis also presents robust shaping approaches. The measured room responses may contain measurement errors or noise and can vary from time to time. These variations may be due to changes in atmospheric conditions (such as temperature or humidity) or due to change in position of objects inside a room. While design approaches over multiple microphone positions have been proposed for design of filters that are robust to change in microphone positions, a more rigorous approach is statistical, involving the inclusion of some statistical constraints into the optimization problem. The thesis presents both the approaches viz., a computationally faster version (using DALM) of the already proposed design over multiple positions and a statistically robust shaping formulation. The latter limits the probability of large errors between expected and obtained response to be less than a specified value. This ensures that the solution is robust to variations in the room response. The shaping algorithm works in the time domain, shaping the temporal characteristics of the room response to a desired form. The frequency response of the shaped response can contain potentially undesirable peaks and troughs. This thesis therefore presents an approach for an efficient projection to improve spectral flatness of the resultant response. This algorithm can be combined with the fast and memory efficient DALM based approach to achieve joint time and frequency shaping. Finally, the thesis also presents a computationally fast algorithm based on DALM for pressure matching used in sound field reproduction. Impulse response shaping is applied in sound field reproduction, showing that the levels of pre-reverberation induced by a temperature change can be reduced. This application is different from impulse response shaping approaches presented in the previous chapters and highlights the flexibility of the algorithm developed in this thesis and its wide range of applications.</p>

Acoustic Room Impulse Response Shaping

<p>Impulse response shaping is a technique for modifying the characteristics of a linear channel to achieve desirable characteristics. The technique is well-known in the field of wireless communication. Acoustic impulse response shaping is used to reduce the effects of reverberation on audio signals propagating inside a room and is thus used for listening room compensation. This thesis addresses innovative approaches for acoustic impulse response shaping. Many techniques have been proposed in the literature for canceling or reducing the effect of reverberation on the audio signal. Impulse response inversion attempts to completely cancel the effect of reverberations whereas impulse response shortening (or shaping) only partly equalizes the room impulse responses. Shortening has less stringent constraints than inversion and this can result in more robust solutions and thus more practically realizable systems. Acoustic impulse response shaping works on measured room impulse responses and designs pre-filters to be placed before the loudspeakers so that the reverberation is reduced at the listening positions. When sampled, the room responses typically contain thousands or tens of thousands (N ) of samples. Thus, the shaping algorithm needs to be computationally fast and memory efficient in order to implement the system in real time. The techniques presented in the literature use interior point methods or steepest descent algorithms, which are computationally slow or require memory of the order of N² . This thesis presents shaping approaches based on the Dual Augmented Lagrangian Method (DALM), known in the literature on sparse reconstruction for its super-linear convergence. The method presented here also makes use of the concept of a Forward Adjoint Oracle (FAO) to make the shaping algorithm memory efficient. Thus, the thesis presents computationally fast and memory efficient shaping algorithms that can be used for practically realizable systems. The thesis also presents robust shaping approaches. The measured room responses may contain measurement errors or noise and can vary from time to time. These variations may be due to changes in atmospheric conditions (such as temperature or humidity) or due to change in position of objects inside a room. While design approaches over multiple microphone positions have been proposed for design of filters that are robust to change in microphone positions, a more rigorous approach is statistical, involving the inclusion of some statistical constraints into the optimization problem. The thesis presents both the approaches viz., a computationally faster version (using DALM) of the already proposed design over multiple positions and a statistically robust shaping formulation. The latter limits the probability of large errors between expected and obtained response to be less than a specified value. This ensures that the solution is robust to variations in the room response. The shaping algorithm works in the time domain, shaping the temporal characteristics of the room response to a desired form. The frequency response of the shaped response can contain potentially undesirable peaks and troughs. This thesis therefore presents an approach for an efficient projection to improve spectral flatness of the resultant response. This algorithm can be combined with the fast and memory efficient DALM based approach to achieve joint time and frequency shaping. Finally, the thesis also presents a computationally fast algorithm based on DALM for pressure matching used in sound field reproduction. Impulse response shaping is applied in sound field reproduction, showing that the levels of pre-reverberation induced by a temperature change can be reduced. This application is different from impulse response shaping approaches presented in the previous chapters and highlights the flexibility of the algorithm developed in this thesis and its wide range of applications.</p>