Frequency-dependent Processing Research Articles

(Why) Do Transparent Hearing Devices Impair Speech Perception in Collocated Noise?

Hearing aids and other hearing devices should provide the user with a benefit, for example, compensate for effects of a hearing loss or cancel undesired sounds. However, wearing hearing devices can also have negative effects on perception, previously demonstrated mostly for spatial hearing, sound quality and the perception of the own voice. When hearing devices are set to transparency, that is, provide no gain and resemble open-ear listening as well as possible, these side effects can be studied in isolation. In the present work, we conducted a series of experiments that are concerned with the effect of transparent hearing devices on speech perception in a collocated speech-in-noise task. In such a situation, listening through a hearing device is not expected to have any negative effect, since both speech and noise undergo identical processing, such that the signal-to-noise ratio at ear is not altered and spatial effects are irrelevant. However, we found a consistent hearing device disadvantage for speech intelligibility and similar trends for rated listening effort. Several hypotheses for the possible origin for this disadvantage were tested by including several different devices, gain settings and stimulus levels. While effects of self-noise and nonlinear distortions were ruled out, the exact reason for a hearing device disadvantage on speech perception is still unclear. However, a significant relation to auditory model predictions demonstrate that the speech intelligibility disadvantage is related to sound quality, and is most probably caused by insufficient equalization, artifacts of frequency-dependent signal processing and processing delays.

Hybrid Wideband Beamforming for Sum Spectral Efficiency Maximization in Millimeter-Wave Relay-Assisted Multiuser MIMO Cognitive Radio Networks

Relay-assisted hybrid beamforming plays an inevitable role in enhancing network coverage, transmission range, and spectral efficiency while simultaneously reducing hardware cost, power consumption, and hardware implementation complexity. This study investigates a cognitive radio network (CRN)-based hybrid wideband transceiver for millimeter-wave (mm-wave) decode-and-forward (DF) relay-assisted multiuser (MU) multiple-input multiple-output (MIMO) systems. It is worth mentioning that the underlying problem has not been addressed so far, which is a real motivation behind the proposed algorithm. The joint optimization of hybrid processing components and the constant amplitude constraints imposed by the analog beamforming solution make this problem non-convex and NP-hard. Furthermore, the analog beamformer common to all sub-carriers is another challenging aspect of the underlying problem. To derive the frequency-flat analog processing component in the radio frequency (RF) domain and frequency-dependent baseband processing matrices in the baseband domain, the original complicated problem is reformulated as two single-hop sum-rate maximization sub-problems. Taking advantage of this decomposition, the sum spectral efficiency is maximized through RF precoding and combining. On the other hand, the impact of interference among transmitted data streams and inter-user interference (IUI) is minimized via baseband processing matrices. Finally, computer simulations are conducted by changing system parameters, considering both perfect and imperfect channel state information (CSI). Simulation results demonstrate that the proposed algorithm achieves performance close to full-complexity precoding and outperforms other well-known hybrid beamforming techniques. Specifically, more than 95% efficiency is achieved with perfect CSI, and more than 90% efficiency is attained under the assumption of 30% error in the estimated channels.

Compensating first reflections in non-anechoic head-related transfer function measurements

Personalized Head-Related Transfer Functions (HRTFs) are needed as part of the binaural sound individualization process in order to provide a high-quality immersive experience for a specific user. Signal processing methods for performing HRTF measurements in non-anechoic conditions are of high interest to avoid the complex and inconvenient access to anechoic facilities. Non-anechoic HRTF measurements capture the effect of room reflections, which should be correctly identified and eliminated to obtain HRTFs estimates comparable to ones acquired in an anechoic setup. This paper proposes a sub-band frequency-dependent processing method for reflection suppression in non-anechoic HRTF signals. Array processing techniques based on Plane Wave Decomposition (PWD) are adopted as an essential part of the solution for low frequency ranges, whereas the higher frequencies are easily handled by means of time-crop windowing methods. The formulation of the model, extraction of parameters and evaluation of the method are described in detail. In addition, a validation case study is presented showing the suppression of reflections from an HRTF measured in a real system. The results confirm that the method allows to obtain processed HRTFs comparable to those acquired in anechoic conditions.

A Four-Element 500-MHz 40-mW 6-bit ADC-Enabled Time-Domain Spatial Signal Processor

Next-generation wireless communication requires phased-array systems with large modulated bandwidths and high energy efficiency, ensuring Gb/s data communication. Conventional phase-shifter-based arrays result in frequency-dependent processing and, therefore, beam-squinting in an array. This work demonstrates a four-element 500-MHz modulated bandwidth true-time-delay-based ADC-enabled spatial signal processor (SSP) with frequency-uniform beamforming, wideband beam-nulling, and multiple independent interference filterings using the Kronecker decomposition. This processor can augment conventional phased-array RF front ends to implement a complete antenna-to-digital solution. The proposed baseband delay-compensating solution in the SSP uses scalable time-domain circuits comprising of time-interleaved voltage-to-time converters followed by asynchronous 6-bit pipeline time-to-digital converters and consumes only 40 mW with a total area of 0.31 mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> in 65-nm CMOS technology.

Influence of spatial frequency and emotion expression on face processing in patients with panic disorder

BackgroundDeficits in facial emotion processing is a major characteristic of patients with panic disorder. It is known that visual stimuli with different spatial frequencies take distinct neural pathways. This study investigated facial emotion processing involving stimuli presented at broad, high, and low spatial frequencies in patients with panic disorder. MethodsEighteen patients with panic disorder and 19 healthy controls were recruited. Seven event-related potential (ERP) components: (P100, N170, early posterior negativity (EPN); vertex positive potential (VPP), N250, P300; and late positive potential (LPP)) were evaluated while the participants looked at fearful and neutral facial stimuli presented at three spatial frequencies. ResultsWhen a fearful face was presented, panic disorder patients showed a significantly increased P100 amplitude in response to low spatial frequency compared to high spatial frequency; whereas healthy controls demonstrated significant broad spatial frequency dependent processing in P100 amplitude. Vertex positive potential amplitude was significantly increased in high and broad spatial frequency, compared to low spatial frequency in panic disorder. Early posterior negativity amplitude was significantly different between HSF and BSF, and between LSF and BSF processing in both groups, regardless of facial expression. LimitationThe possibly confounding effects of medication could not be controlled. ConclusionsDuring early visual processing, patients with panic disorder prefer global to detailed information. However, in later processing, panic disorder patients overuse detailed information for the perception of facial expressions. These findings suggest that unique spatial frequency-dependent facial processing could shed light on the neural pathology associated with panic disorder.

Early visual processing deficits in patients with schizophrenia during spatial frequency-dependent facial affect processing

Abnormal facial emotion recognition is considered as one of the key symptoms of schizophrenia. Only few studies have considered deficits in the spatial frequency (SF)-dependent visual pathway leading to abnormal facial emotion recognition in schizophrenia. Twenty-one patients with schizophrenia and 19 matched healthy controls (HC) were recruited for this study. Event-related potentials (ERP) were measured during presentation of SF-modulated face stimuli and their source imaging was analyzed. The patients showed reduced P100 amplitude for low-spatial frequency (LSF) pictures of fearful faces compared with the HC group. The P100 amplitude for high-spatial frequency (HSF) pictures of neutral faces was increased in the schizophrenia group, but not in the HC group. The neural source activities of the LSF fearful faces and HSF neutral faces led to hypo- and hyperactivation of the frontal lobe of subjects from the schizophrenia group and HC group, respectively. In addition, patients with schizophrenia showed enhanced N170 activation in the right hemisphere in the LSF condition, while the HC group did not. Our results suggest that deficits in the LSF-dependent visual pathway, which involves magnocellular neurons, impair early visual processing leading to dysfunctional facial emotion recognition in schizophrenia. Moreover, it suggests impaired bottom-up processing rather than top-down dysfunction for facial emotion recognition in these patients.

Frequency-dependent signal processing in apical dendrites of hippocampal CA1 pyramidal cells

Depending on an animal’s behavioral state, hippocampal CA1 pyramidal cells receive distinct patterns of excitatory and inhibitory synaptic inputs. The time-dependent changes in the frequencies of these inputs and the nonuniform distribution of voltage-gated channels lead to dynamic fluctuations in membrane conductance. In this study, using a whole-cell patch-clamp method, we attempted to record and analyze the frequency dependencies of membrane responsiveness in Wistar rat hippocampal CA1 pyramidal cells following noise current injection directly into dendrites and somata under pharmacological blockade of all synaptic inputs. To estimate the frequency-dependent properties of membrane potential, membrane impedance was determined from the voltage response divided by the input current in the frequency domain. The cell membrane of most neurons showed low-pass filtering properties in all regions. In particular, the properties were strongly expressed in the somata or proximal dendrites. Moreover, the data revealed nonuniform distribution of dendritic impedance, which was high in the intermediate segment of the apical dendritic shaft (∼220–260μm from the soma). The low-pass filtering properties in the apical dendrites were more enhanced by membrane depolarization than those in the somata. Coherence spectral analysis revealed high coherence between the input signal and the output voltage response in the theta–gamma frequency range, and large lags emerged in the distal dendrites in the gamma frequency range. Our results suggest that apical dendrites of hippocampal CA1 pyramidal cells integrate synaptic inputs according to the frequency components of the input signal along the dendritic segments receiving the inputs.

Method for Reproducing Natural or Modified Spatial Impression in Multichannel Listening

The invention concerns a method for reproducing spatial impression of existing spaces in multichannel or binaural listening. It consists of following steps/phases: a) Recording of sound or impulse response of a room using multiple microphones, b) Time- and frequency-dependent processing of impulse responses or recorded sound, c) Processing of sound to multichannel loudspeaker setup in order to reproduce spatial properties of sound as they were in recording room, and (alternative to c), d) Processing of impulse response to multichannel loudspeaker setup, and convolution between rendered responses and an arbitrary monophonic sound signal to introduce the spatial properties of the measurement room to the multichannel reproduction of the arbitrary sound signal, and is applied in sound studio technology, audio broadcasting, and in audio reproduction.

Discrete cosine transform particle filter speech enhancement

A discrete cosine transform (DCT) domain speech enhancement algorithm is proposed that models the evolution of speech DCT coefficients as a time-varying autoregressive process. Rao-Blackwellized particle filter (RBPF) techniques are used to estimate the model parameters and recover the clean signal coefficients. Using very low-order models for each coefficient and operating at a decimated frame rate, the proposed approach provides a significant complexity reduction compared to the standard full-band RBPF speech enhancement algorithm. In addition to the complexity gains, performance is also improved. Modeling the speech signal in the DCT-domain is shown to provide a better fit in spectral troughs, leading to more noise reduction and less speech distortion. To illustrate possible frequency-dependent processing strategies, a hybrid structure is proposed that offers a complexity/performance trade-off by substituting a simple DCT Wiener filter for the DCT-RBPF in some bands. In comparisons with high performing speech enhancement algorithms using wideband speech and noise, the proposed DCT-RBPF algorithm achieves higher scores on objective quality and intelligibility measures.

Early frequency-dependent information processing and cortical control in the whisker pathway of the rat: Electrophysiological study of brainstem nuclei principalis and interpolaris

The rat facial whiskers form a high-resolution sensory apparatus for tactile information coding and are used by these animals for the exploration and perception of their environment. Previous work on the rat vibrissae system obtained evidence for vibration-based feature extraction by the whiskers, texture classification by the cortical neurons, and “low-pass,” “high-pass,” and “band-pass” filtering properties in both thalamic and cortical neurons. However, no data are available for frequency-dependent information processing in the brainstem sensory trigeminal complex (STC), the first relay station of the vibrissae pathway. In the present paper, we studied the frequency-dependent processing characteristics of the STC nuclei that mainly project to the thalamus, nuclei principalis, and interpolaris. This is the first time that STC nuclei have been studied together via a wide range of stimulation frequencies (1–40 Hz), four different and complementary metrics, and the same experimental protocol. Moreover, the role of corticofugal projection to these nuclei as well as the influence of input from the whiskers has been analyzed. We show that both nuclei perform frequency-dependent coding of tactile information: low pass and band-pass filtering occurs for the spiking rate in short post-stimuli time intervals, high-pass and band-pass filtering occurs for the spiking rate in long trains of stimuli, and an increase of response latencies and low pass filtering occurs for phase-locked stimuli. These information-processing characteristics are neither imposed by the sensorimotor cortex nor introduced by the afferent fibres. The sensorimotor cortex exerts a distinct modulatory effect on each nucleus.

Regional Specification of Threshold Sensitivity and Response Time in CBA/CaJ Mouse Spiral Ganglion Neurons

Previous studies of spiral ganglion neuron electrophysiology have shown that specific parameters differ according to cochlear location, with apical neurons being distinctly different from basal neurons. To align these features more precisely along the tonotopic axis of the cochlea, we developed a novel spiral ganglion culture system in which positional information is retained. Patch-clamp recordings made from neurons of known gangliotopic location revealed two basic firing pattern distributions. Membrane characteristics related to spike timing, such as accommodation, latency and onset tau, were distinctly heterogeneous, yet when averaged, they were distributed in a graded manner along the length of the cochlea. Action potential threshold levels also displayed a wide range, the averages of which were distributed nonmonotonically such that neurons with the greatest sensitivity were localized to the mid-regions of the ganglion. These studies shed new light on the complexity and sophistication of the intrinsic firing features of spiral ganglion neurons. Because timing-related elements are organized in an overall tonotopic manner, it is hypothesized that they contribute to aspects of frequency-dependent acoustic processing. On the other hand, the different distribution of threshold levels, with the greatest sensitivity in the middle region of the tonotopic map, suggests that this neuronal parameter is regulated differently and thus may contribute a distinct realm of auditory sensory processing.

Subband-Based Blind Separation for Convolutive Mixtures of Speech

We propose utilizing subband-based blind source separation (BSS) for convolutive mixtures of speech. This is motivated by the drawback of frequency-domain BSS, i.e., when a long frame with a fixed long frame-shift is used to cover reverberation, the number of samples in each frequency decreases and the separation performance is degraded. In subband BSS, (1) by using a moderate number of subbands, a sufficient number of samples can be held in each subband, and (2) by using FIR filters in each subband, we can manage long reverberation. We confirm that subband BSS achieves better performance than frequency-domain BSS. Moreover, subband BSS allows us to select a separation method suited to each subband. Using this advantage, we propose efficient separation procedures that consider the frequency characteristics of room reverberation and speech signals (3) by using longer unmixing filters in low frequency bands and (4) by adopting an overlap-blockshift in BSS's batch adaptation in low frequency bands. Consequently, frequency-dependent subband processing is successfully realized with the proposed subband BSS.

Frequency-dependent processing in the vibrissa sensory system.

The vibrissa sensory system is a key model for investigating principles of sensory processing. Specific frequency ranges of vibrissa motion, generated by rodent sensory behaviors (e.g., active exploration or resting) and by stimulus features, characterize perception by this system. During active exploration, rats typically sweep their vibrissae at approximately 4-12 Hz against and over tactual surfaces, and during rest or quiescence, their vibrissae are typically still (<1 Hz). When a vibrissa is swept over an object, microgeometric surface features (e.g., grains on sandpaper) likely create higher frequency vibrissa vibrations that are greater than or equal to several hundred Hertz. In this article, I first review thalamic and cortical neural responses to vibrissa stimulation at 1-40 Hz. I then propose that neural dynamics optimize the detection of stimuli in low-frequency contexts (e.g., 1 Hz) and the discrimination of stimuli in the whisking frequency range. In the third section, I describe how the intrinsic biomechanical properties of vibrissae, their ability to resonate when stimulated at specific frequencies, may promote detection and discrimination of high-frequency inputs, including textured surfaces. In the final section, I hypothesize that distinct low- and high-frequency processing modes may exist in the somatosensory cortex (SI), such that neural responses to stimuli at 1-40 Hz do not necessarily predict responses to higher frequency inputs. In total, these studies show that several frequency-specific mechanisms impact information transmission in the vibrissa sensory system and suggest that these properties play a crucial role in perception.

Frequency dependence and gender effects in visual cortical regions involved in temporal frequency dependent pattern processing.

Neural response to flickering stimuli has been shown to be frequency dependent in the primary visual cortex. Controversial gender differences in blood oxygen level dependent (BOLD) amplitude upon 6 and 8 Hz visual stimulation have been reported. In order to analyze frequency and gender effects in early visual processing we employed a passive graded task paradigm with a dartboard stimulus combining eight temporal frequencies from 0 to 22 Hz in one run. Activation maps were calculated within Statistical Parametric Mapping, and BOLD amplitudes were estimated for each frequency within the striate and extrastriate visual cortex. The BOLD amplitude was found to steadily rise up to 8 Hz in BA 17 and 18 with an activation plateau at higher frequencies. In addition, we observed a laterality effect in the striate cortex with higher BOLD contrasts in the right hemisphere in men and in women. BOLD response rises similarly in men and women up to 8 Hz but with lower amplitudes in women at 4, 8, and 12 Hz (30% lower). No frequency effect above 1 Hz was found in the extrastriate visual cortex. There was also a regional specific gender difference. Men activated more in the right lingual gyrus (BA 18) and the right cerebellum compared with women, whereas women showed more activation in the right inferior temporal gyrus (BA 17). The study indicates that frequency dependent processing at the cortical level is limited to the striate cortex and may be associated with a more global information processing (right hemisphere dominance), particularly in men. The finding of significantly lower BOLD amplitudes in women despite previously shown larger VEP (visual evoked potential) amplitudes might suggest gender differences in cerebral hemodynamics (baseline rCBV, rCBF, or neurovascular coupling). The regional distinction points at additional differences in psychological processing even when using a simple visual stimulus.

Space-time processing for multichannel synthetic aperture radar

Synthetic aperture radar (SAR) provides high-resolution images of a non-moving ground scene, but fails to indicate the presence and position of moving objects. As in airborne MTI (moving-target indication) systems the solution to this problem is to use an array of antennas or subapertures and several receiving channels ('MSAR', or multichannel SAR), and to apply multichannel clutter suppression. One of the most efficient methods is adaptive space-time processing (STAP), which can be simplified to frequency-dependent spatial processing in the Doppler domain. Some of these techniques applied to SAR are reviewed and illustrated with data gathered by the German experimental multichannel SAR system 'AER-II'.

Modifications to nonlinear processing for recruitment of loudness.

The time-varying frequency-dependent processing (TVFD) [J. C. Rutledge and M. A. Clements, Proc. IEEE ICASSP, 3641–3644 (1991)] was designed to adjust to changing speech input on both time and frequency basis. Due to inherent problems with the processing technique, some spectral smearing occurs [J. Acoust. Soc. Am. 89, 1974 (A) (1991)]. The processing has been modified to maintain the time-varying frequency-dependent nature, but reduces the smearing effect. A sinusoidal speech model is used with the compensation processing. Appropriate gains for the sinusoid amplitudes are calculated every 5 ms. In the modified processing scheme, the gain determined for the largest peak in each frequency band is applied to all components in that band. This maintains the relative amplitude ratio between neighboring peaks in the frequency spectrum. The compensation algorithm is presented here along with preliminary performance results based on the objective measures described in another paper at this meeting.