Crosstalk Cancellation System Research Articles

The localization of virtual source reproduced by the crosstalk cancellation system under different direct-to-reverberation energy ratios conditions

This study explores the localization of virtual sources reproduced by the crosstalk cancellation (CTC) system under reverberation environments with different direct-to-reverberation energy ratios (DRRs). Binaural room impulse responses in rectangle rooms are simulated by high-order image source method. Two independent key variables, the reverberation time (RT) and the distance of the sound source to the listener, are employed to manipulate DRR through simulation. Subsequently, a subjective localization experiment based on the CTC system is virtually conducted using earphone reproduction. The results show that the azimuth localization in horizontal plane is almost impervious by RT but is subjected to the change of the source distance. Specifically, as the distance of sound source increases, the perceived azimuth of lateral virtual sources exhibits a bias towards the front, accompanied by larger variances. The results indicate that reflections with small delays have a more detrimental effect on sound localization compared to the late reverberation with large intensity, which may be associated with the inhibition of late reflections based on the precedence effect. Additionally, the localization data are analyzed and explained using binaural cues, including the interaural cross-correlation coefficient, the interaural time difference (ITD), and interaural level difference (ILD).

Analysis of cross-talk cancellation of bilateral bone conduction stimulation

When presenting a stereo sound through bilateral stimulation by two bone conduction transducers (BTs), part of the sound at the left side leaks to the right side, and vice versa. The sound transmitted to the contralateral cochlea becomes cross-talk, which can affect space perception. The negative effects of the cross-talk can be mitigated by a cross-talk cancellation system (CCS). Here, a CCS is designed from individual bone conduction (BC) transfer functions using a fast deconvolution algorithm. The BC response functions (BCRFs) from the stimulation positions to the cochleae were obtained by measurements of BC evoked otoacoustic emissions (OAEs) of 10 participants. The BCRFs of the 10 participants showed that the interaural isolation was low. In 5 of the participants, a cross-talk cancellation experiment was carried out based on the individualized BCRFs. Simulations showed that the CCS gave a channel separation (CS) of more than 50 dB in the 1–3 kHz range with appropriately chosen parameter values. Moreover, a localization test showed that the BC localization accuracy improved using the CCS where a 2–4.5 kHz narrowband noise gave better localization performance than a broadband 0.4–10 kHz noise. The results indicate that using a CCS with bilateral BC stimulation can improve interaural separation and thereby improve spatial hearing by bilateral BC.

Influence of first-order lateral reflections on the localization of virtual source reproduced by crosstalk cancellation system

This study elucidates the influence of first-order lateral reflections on the localization of virtual sources reproduced by a crosstalk cancellation system. First, an experimental study was conducted to examine how the reflections with a delay within the scope of the summing localization and the precedence effect influence the localization of virtual sources with different frequency bands and target azimuths. The results show that the localization of virtual sources is influenced due to the reflections with a delay below the low limit of the precedence effect (1 ms universally), and the influence degree is related to the frequency band and target azimuth. When the delay is further increased, the effect of reflected sound is almost negligible. Particularly, for a virtual source in the region outside the loudspeaker on the contralateral side of the reflecting surface (at -60° or -90°), the perceived azimuth under reflections with a small delay was more lateral than that without reflections. Then, simulations were conducted under the same conditions as the experiments. Based on the binaural signals modified by the inhibition function of the precedence effect, binaural cues, including interaural phase delay difference (ITDp) and interaural level difference, were calculated to explain the experimental results. Particularly, the average ITDp over frequency can qualitatively predict the localization results below 1.5 kHz from the subjective experiment in most cases.

Improved Low-Frequency Crosstalk Cancellation in Bone Conduction Using Bone Transducers and Probe Microphone

A bone conduction (BC) sound presented on either side of the head will travel to the cochleae in both ears, and this crosstalk phenomenon is considered one factor limiting the benefits of binaural hearing with BC. Previous studies have demonstrated the feasibility of measuring the phase and level required for crosstalk cancellation at the cochlea; however, given a human subject’s inability to consistently detect low frequencies, this method is limited to cancellations at frequencies above 1000 Hz. This study describes an alternative approach for implementing a crosstalk cancellation system for low frequencies by measuring ear-canal sound pressure (ECSP). Since the ear canal is close to the cochlea, we hypothesized that altering ECSP in response to a BC stimulation may be used to achieve crosstalk cancellation at the cochlea. Our approach relies on ECSP measurements to estimate impulse responses (IRs) from bone transducers to a probe microphone in the ear canal. The IRs are then used to predict the phase and level required for crosstalk cancellation at the probe microphone’s location. To confirm the hypothesis, we measured tone reception threshold (TRT), the lowest tone level participants could detect, under two conditions: with and without crosstalk cancellation. Although crosstalk cancellation was designed to occur at the probe microphone and not at the cochlea, the TRT results showed that participants were still able to perceive cancellations at frequencies below 1000 Hz.

A Multiple Listener Crosstalk Cancellation System Using Loudspeaker-Dependent Regularization

Binaural audio requires the use of crosstalk cancellation if reproduced using loudspeakers. A three-listener crosstalk cancellation system has been designed and built as part of this work. Simulations for different loudspeaker distributions are presented and a large system span is shown to increase low-frequency crosstalk cancellation performance while a denser loudspeaker distribution in front of a given listener increases mid to high-frequency crosstalk cancellation. The system's performance under perturbation of the listeners and loudspeakers is investigated and at high frequencies loudspeakers further away from any given listener are shown to be affected more by perturbations than those nearer the listener. To this issue, a novel implementation of weighting loudspeaker source strengths using loudspeaker-dependent regularization is developed and optimized for use in this system. Hence, at high frequencies just loudspeakers close to the listener are used. This is shown to create a more robust solution than traditional crosstalk cancellation filter design when the system has undergone perturbations.

A modal analysis of multichannel crosstalk cancellation systems and their relationship to amplitude panning

The single-listener multichannel crosstalk cancellation system is analysed using the singular value decomposition. Analytic expressions for the singular system are derived considering a sound-field of point sources placed in the far-field and in free-field conditions. The derived singular system yields theoretical insight into the benefit of multichannel loudspeaker geometries over the conventional two-channel system. From the singular system the source strength solution is derived for a target far-field virtual source. The low frequency approximation of the derived source strengths is an amplitude panning function. This panning function is a generalisation of the sine law solution that allows for head rotation and asymmetric loudspeaker geometry. When the geometry is symmetric about the median plane of the listener the low frequency sources strengths are the minimum ℓ2 norm solution of the multichannel sine law. The low frequency approximation is also shown to be representative when the free-field assumption is relaxed.

Unilateral crosstalk cancellation in normal hearing participants using bilateral bone transducers.

It is possible to psychophysically measure the phase and level of bone conducted sound at the cochleae using two bone transducers (BTs) [Mcleod and Culling (2019). J. Acoust Soc. Am. 146, 3295 - 3301]. The present work uses such measurements to improve masked thresholds by using the phase and level values to create a unilateral crosstalk cancellation system. To avoid changes in the coupling of the BT to the head, testing of tone and speech reception thresholds with and without crosstalk cancellation had to be performed immediately following the measurements without adjustment of the BT. To achieve this, a faster measurement method was created. Previously measured phase and level results were interpolated to predict likely results for new test frequencies. Testing time to collect the necessary phase and level values was reduced to approximately 15 min by exploiting listeners' previous measurements. The inter-cochlear phase difference and inter-cochlear level difference were consistent between experimental sittings in the same participant but different between participants. Addition of a crosstalk cancellation signal improved tone and speech reception thresholds for tones/speech presented with one BT and noise presented on the other by an average of 12.1 dB for tones and 13.67 dB for speech.

A Stochastic Approximation Method with Enhanced Robustness for Crosstalk Cancellation

The objective of acoustic crosstalk cancellation is to use loudspeakers to deliver prescribed binaural signals (that reproduce a particular auditory scene) to a listener's ears, which is useful for 3-D audio applications. In practice, the actual transfer function matrix will differ from the design matrix, because of either the listener's head movement or rotation, etc. Crosstalk cancellation system (CCS) is very non-robust to these perturbations. Generally, in order to improve the robustness of CCS, several pairs of loudspeakers are needed whose position varies continuously as frequency varies. With the help of assumed stochastic analysis, we propose a stochastic robust approximation crosstalk cancellation method based on random perturbation matrix modeling the variations of the transfer function matrix. Under the free-field condition, simulation results demonstrate the effectiveness of the proposed method.

Measurements of inter-cochlear level and phase differences of bone-conducted sound

Bone-anchored hearing aids are a widely used method of treating conductive hearing loss, but the benefit of bilateral implantation is limited due to interaural cross-talk. The present study measured the phase and level of pure tones reaching each cochlea from a single, mastoid placed bone transducer on normal hearing participants. In principle, the technique could be used to implement a cross-talk cancellation system in those with bilateral bone conductors. The phase and level of probe tones over two insert earphones was adjusted until they canceled sound from a bone transducer (i.e., resulting in perceived silence). Testing was performed in 50-Hz steps between 0.25 and 8 kHz. Probe phase and level results were used to calculate inter-cochlear level and phase differences. The inter-cochlear phase differences of the bone-conducted sound were similar for all three participants showing a relatively linear increase between 4 and 8 kHz. The attenuation characteristics were highly variable over the frequency range as well as between participants. This variability was thought to be related to differences in skull dynamics across the ears. Repeated measurements of cancellation phase and level of the same frequency produced good consistency across sessions from the same participant.

A Linear Robust Binaural Sound Reproduction System with Optimal Source Distribution Strategy

Crosstalk cancellation system plays an important role in binaural sound playback using loudspeakers and has attracted many researchers' interest. However, limited sweet spot is still a challenge especially when the head is laterally misaligned. In this report the optimization of a linear binaural playback system is proposed, in which the optimal source distribution strategy in a linear array configuration is combined with the technique of multiple control points. The proposed method aims to find a good trade-off between the crosstalk cancellation performance and the robustness against the head misalignment. Both simulations and experiments demonstrate the efficacy of the proposed method.

Design and Implementation Analysis of OSD based Audio Crosstalk Cancellation with Multi-Channel Inputs on DSP Processors

To overcome the basic system inversion problems in conventional crosstalk cancellation systems, the three channel Optimum Source Distribution (OSD) was developed by Takashi et al., that provides balance between in-phase and out of phase components. The main difficulty in this system is real-time implementation of cross talk cancellation filters on DSP platforms, particularly when filter lengths are very long with system operates on multichannel inputs. This paper discusses the implementation complexities and proposes an efficient approach to reduce the power consumption. It also discusses efficient usage of available processor memory. By utilizing the processor resources and existing frequency domain techniques, this approach would be one of best methods for long filters. The mathematical model, with efficient design for floating point DSP processors, clearly explains the optimization methods at algorithmic and instruction levels. The computational complexity of the proposed method was measured for various multi-channel input sources and the comparison was shown. The results indicate that the proposed method provides efficient computations than existing methods. Keywords: Convolution, Crosstalk Cancellation, Optimal Source Distribution, Overlap Save Method, Uniform Partitioned Convolution

Development of dynamic crosstalk cancellation system for multiple-listener binaural reproduction

Development of dynamic crosstalk cancellation system for multiple-listener binaural reproduction

A Framework for the Calculation of Dynamic Crosstalk Cancellation Filters

Dynamic crosstalk cancellation (CTC) systems commonly find use in immersive virtual reality (VR) applications. Such dynamic setups require extremely high filter update rates, so filter calculation is usually performed in the frequency-domain for higher efficiency. This paper proposes a general framework for the calculation of dynamic CTC filters to be used in immersive VR applications. Within this framework, we introduce a causality constraint to the frequency-domain calculation to avoid undesirable wrap-around effects and echo artifacts. Furthermore, when regularization is applied to the CTC filter calculation, in order to limit the output levels at the loudspeakers, noncausal artifacts appear at the CTC filters and the resulting ear signals. We propose a global minimum-phase regularization to convert these anti-causal ringing artifacts into causal artifacts. Finally, an aspect that is especially critical for dynamic CTC systems is the filter switch between active loudspeakers distributed in a surround audio-visual display system with 360° of freedom of operator orientation. Within this framework we apply a weighted filter calculation to control the filter switch, which allows the loudspeakers' contribution to be windowed in space, resulting in a smooth filter transition.

Sound localization in individualized and non-individualized crosstalk cancellation systems

The sound-source localization provided by a crosstalk cancellation (CTC) system depends on the head-related transfer functions (HRTFs) used for the CTC filter calculation. In this study, the horizontal- and sagittal-plane localization performance was investigated in humans listening to individualized matched, individualized but mismatched, and non-individualized CTC systems. The systems were simulated via headphones in a binaural virtual environment with two virtual loudspeakers spatialized in front of the listener. The individualized mismatched system was based on two different sets of listener-individual HRTFs. Both sets provided similar binaural localization performance in terms of quadrant, polar, and lateral errors. The individualized matched systems provided performance similar to that from the binaural listening. For the individualized mismatched systems, the performance deteriorated, and for the non-individualized mismatched systems (based on HRTFs from other listeners), the performance deteriorated even more. The direction-dependent analysis showed that mismatch and lack of individualization yielded a substantially degraded performance for targets placed outside of the loudspeaker span and behind the listeners, showing relevance of individualized CTC systems for those targets. Further, channel separation was calculated for different frequency ranges and is discussed in the light of its use as a predictor for the localization performance provided by a CTC system.

A Stereo Crosstalk Cancellation System Based on the Common-Acoustical Pole/Zero Model

Crosstalk cancellation plays an important role in displaying binaural signals with loudspeakers. It aims to reproduce binaural signals at a listener's ears via inverting acoustic transfer paths. The crosstalk cancellation filter should be updated in real time according to the head position. This demands high computational efficiency for a crosstalk cancellation algorithm. To reduce the computational cost, this paper proposes a stereo crosstalk cancellation system based on common-acoustical pole/zero (CAPZ) models. Because CAPZ models share one set of common poles and process their zeros individually, the computational complexity of crosstalk cancellation is cut down dramatically. In the proposed method, the acoustic transfer paths from loudspeakers to ears are approximated with CAPZ models, then the crosstalk cancellation filter is designed based on the CAPZ transfer functions. Simulation results demonstrate that, compared to conventional methods, the proposed method can reduce computational cost with comparable crosstalk cancellation performance.

Channel separation of crosstalk cancellation systems with mismatched and misaligned sound sources

Loudspeakers in virtual sound imaging systems are usually modeled as omnidirectional monopole sources. These models are, however, only an approximation for the low frequency range. This paper presents an analytical model of crosstalk cancellation systems in a free field which takes into account the scattering and spatial characteristics of the sound sources. Based on the proposed model, the effects caused by the spatial characteristics of the sound source and its misalignments on the performance of the crosstalk cancellation system are studied numerically. It is found that although the factors such as the directivity of the sound sources and the distance between the sound sources and receiver affect the performance of the system to a certain extent, the channel separation of the crosstalk cancellation system, however, is most sensitive to the misalignment of the subtended angle of the sound sources. Therefore, if highly accurate binaural cues are required in practical applications, the type and characteristics of the playback sound sources, their locations, and orientations all should be considered carefully.

Two Listeners Crosstalk Cancellation System Modelled by Four Point Sources and Two Rigid Spheres

In virtual acoustic imaging systems, the perception of a sound source anywhere in space can theoretically be reproduced for one listener by using only two loudspeaker and an appropriate set of filters, called crosstalk cancellation (CTC) filters. However, the ideal position of the loudspeakers in such systems is still a question that is currently addressed by many researchers. Several analytical models with varying degrees of complexity have been used to analyze this matter. The fact is that, so far, all implemented CTC systems were built for a single listener use. When it comes to two listener CTC systems, the conditioning of the matrix of transfer functions between the loudspeakers and the listener's ear seems to be more irregular than the conditioning of the matrix for a one listener CTC system. Using a simplified model made it possible to verify that the position of the sound sources also plays a major role as far as the two listeners system's performance is concerned. Now, the influence of the presence of the listener's head in this model is evaluated. The free-field model of a two listener CTC system is expanded by modelling the listeners' heads as two rigid spheres. Using this new model an optimal source displacement is calculated based on two potential source distribution arrangements, namely a linear and a circular source distribution.

On Crosstalk Cancellation and Equalization With Multiple Loudspeakers for 3-D Sound Reproduction

People prefer to be able to enjoy spatial audio without wearing a headphone. Such a tethered device is anyway inconvenient and undesirable, if not cumbersome. Alternatively, 3D sound can be delivered to a listener with loudspeakers. However, crosstalk arises, and the rendered binaural signals are distorted by room reverberation when arriving at the listener's two ears, which lead to the need for a crosstalk cancellation and equalization (CTCE) system. Classical CTCE systems employ only two loudspeakers, and their performance is usually unsatisfactory in practice. While the idea of using more loudspeakers has been investigated, it was never shown why using more loudspeakers is theoretically more advantageous for CTCE. In this letter, we will study this problem and demonstrate that with two loudspeakers, only a least-squares (LS) solution can be obtained, while using multiple loudspeakers, we have more options: either an LS solution or an exact solution for perfect CTCE. These findings are justified by simulations using real impulse responses measured in the varechoic chamber at Bell Labs.

Upmixing and Downmixing Two-channel Stereo Audio for Consumer Electronics

In this comprehensive study, algorithms for upmixing, downmixing, and joint up/downmixing are examined and compared. Five upmixing algorithms based on signal decorrelation and reverberation are employed to convert two-channel stereo signals to jive-channel signals. For downmixing, methods ranging from mixing with simple gain adjustment to more sophisticated head related transfer function (HRTF) filtering and crosstalk cancellation system (CCS) are utilized to downmix the center channel and the surround channels into the available two frontal loudspeakers. For situations where only two-channel content and loudspeakers are available, a number of up/down mixing schemes are used to simulate a virtual surround environment. Emphasis of comparison is placed on two consumer electronic products: a 5.1 home theater system and a dual-loudspeaker MP3 handset. The effect of loudspeaker spacing on rendering performance is examined. Listening tests are conducted to compare the processing methods in terms of three levels of subjective indices. The results are processed by using the Multi-Analysis Of VAriance (MANOVA) to justify the statistical significance, followed by a multiple regression analysis to correlate the auditory preference with various timbral and spatial attributes.

The binaural performance of a cross-talk cancellation system with matched or mismatched setup and playback acoustics

Cross-talk cancellation is a method for synthesizing virtual auditory space using loudspeakers. One implementation is the "Optimal Source Distribution" technique [T. Takeuchi and P. Nelson, J. Acoust. Soc. Am. 112, 2786-2797 (2002)], in which the audio bandwidth is split across three pairs of loudspeakers, placed at azimuths of +/-90 degrees, +/-15 degrees, and +/-3 degrees, conveying low, mid, and high frequencies, respectively. A computational simulation of this system was developed and verified against measurements made on an acoustic system using a manikin. Both the acoustic system and the simulation gave a wideband average cancellation of almost 25 dB. The simulation showed that when there was a mismatch between the head-related transfer functions used to set up the system and those of the final listener, the cancellation was reduced to an average of 13 dB. Moreover, in this case the binaural interaural time differences and interaural level differences delivered by the simulation of the optimal source distribution (OSD) system often differed from the target values. It is concluded that only when the OSD system is set up with "matched" head-related transfer functions can it deliver accurate binaural cues.