Spatial Audio Techniques Research Articles

Binaural Audio in Hybrid Meetings: Effects on Speaker Identification, Comprehension, and User Experience

In 2020, we have witnessed global experimentation of remote co-working, co-learning, and co-habiting, leading to the re-emergence of a collective search for platforms and paradigms that can optimally coalesce the virtual and physical settings - what has been studied as "hybrid models". In this context, we examine the opportunities that the advances in Spatial Audio techniques can create to improve hybrid meetings. Concretely, we present a controlled study in which 84 participants used an online platform to follow six pre-recorded semi-scripted dialogues. The videos were around two minutes long and each of them simulated a piece of conversation in the physical meeting room among three actors who played the role of co-located attendees. The six videos represented six conditions: three auditive formats, (x2) once co-located attendees wore face masks, and once without masks. We compared the experiences of the participants (remote attendees) in these six conditions. Analyzing three types of data, namely, comprehension/memory test results, self-reported ratings, and eye-tracking, we have found reinforcing evidence that demonstrates the benefits of binaural audio in hybrid settings.

Psychoacoustic Principle, Methods, and Problems with Perceived Distance Control in Spatial Audio

One purpose of spatial audio is to create perceived virtual sources at various spatial positions in terms of direction and distance with respect to the listener. The psychoacoustic principle of spatial auditory perception is essential for creating perceived virtual sources. Currently, the technical means for recreating virtual sources in different directions of various spatial audio techniques are relatively mature. However, perceived distance control in spatial audio remains a challenging task. This article reviews the psychoacoustic principle, methods, and problems with perceived distance control and compares them with the principles and methods of directional localization control in spatial audio, showing that the validation of various methods for perceived distance control depends on the principle and method used for spatial audio. To improve perceived distance control, further research on the detailed psychoacoustic mechanisms of auditory distance perception is required.

The Effect of Partial Time-Frequency Masking of the Direct Sound on the Perception of Reverberant Speech

The perception of sound in real-life acoustic environments, such as enclosed rooms or open spaces with reflective objects, is affected by reverberation. Hence, reverberation is extensively studied in the context of auditory perception, with many studies highlighting the importance of the direct sound for perception. Based on this insight, speech processing methods often use time-frequency (TF) analysis to detect TF bins that are dominated by the direct sound, and then use the detected bins to reproduce or enhance the speech signals. The detection of bins dominated by the direct sound is typically based on an objective measure, such as the direct-to-reverberant ratio (DRR). However, the relation between the DRR in the TF bins and the spatial perception of the reverberant sound which is reproduced from these bins is still not clear. It is the aim of this paper to provide some insights into this relation, specifically for reverberant speech, focusing on bins with high DRR. This is performed using a listening experiment, where high DRR bins within a reverberant speech signal have been masked in the TF domain, based on various DRR thresholds. The results show that the percentage of high-DRR TF bins that were masked may better indicate the quality of spatial perception, compared to the specific value of the DRR threshold. The insights from this work could be incorporated into spatial audio techniques that reproduce the direct sound of reverberant speech, and potentially improve spatial perception. This was illustrated with an implementation of directional audio coding that was studied with an additional listening experiment supporting the previously described results.

Ambisonics and wideband matched-filter approach for bat biosonar study

We previously introduced a method of bat echolocation signal measurement and analysis for target angle estimation using a custom-built high-frequency (20–80 kHz) soundfield microphone and spatial audio techniques. The method provided precise angle estimates of multiple targets. This presentation will provide details and results of expanding the processing of these spatial audio signals using a wideband matched-filter. The custom-built ultrasonic soundfield microphone recorded a static bat’s echolocation signals directly in front of the bat’s head. The measured audio signal in B-format was processed and reproduced for all directions with an increment of 1 deg in azimuth and elevation using Ambisonic audio processing techniques. A matched-filter algorithm was developed and produced wideband ambiguity functions (WAF) of transmitted signals from a high-frequency transmitter or bats. The wideband matched-filter outputs filter responses of the reproduced signals in time domain for all directions. The target estimate accompanying the strongest filter response provides the range, normal velocity, angle, and elevation of the target. This presentation shows the hardware and software development including experimental validation to establish this new method for bat biosonar study.We previously introduced a method of bat echolocation signal measurement and analysis for target angle estimation using a custom-built high-frequency (20–80 kHz) soundfield microphone and spatial audio techniques. The method provided precise angle estimates of multiple targets. This presentation will provide details and results of expanding the processing of these spatial audio signals using a wideband matched-filter. The custom-built ultrasonic soundfield microphone recorded a static bat’s echolocation signals directly in front of the bat’s head. The measured audio signal in B-format was processed and reproduced for all directions with an increment of 1 deg in azimuth and elevation using Ambisonic audio processing techniques. A matched-filter algorithm was developed and produced wideband ambiguity functions (WAF) of transmitted signals from a high-frequency transmitter or bats. The wideband matched-filter outputs filter responses of the reproduced signals in time domain for all directions. The target est...

Interaural Level Difference Optimization of Binaural Ambisonic Rendering

Ambisonics is a spatial audio technique appropriate for dynamic binaural rendering due to its sound field rotation and transformation capabilities, which has made it popular for virtual reality applications. An issue with low-order Ambisonics is that interaural level differences (ILDs) are often reproduced with lower values when compared to head-related impulse responses (HRIRs), which reduces lateralization and spaciousness. This paper introduces a method of Ambisonic ILD Optimization (AIO), a pre-processing technique to bring the ILDs produced by virtual loudspeaker binaural Ambisonic rendering closer to those of HRIRs. AIO is evaluated objectively for Ambisonic orders up to fifth order versus a reference dataset of HRIRs for all locations on the sphere via estimated ILD and spectral difference, and perceptually through listening tests using both simple and complex scenes. Results conclude AIO produces an overall improvement for all tested orders of Ambisonics, though the benefits are greatest at first and second order.

Bat biosonar study using spatial audio techniques

Bats have highly specialized hearing adaptations that give them target detection, localization, and interception abilities that far surpass any man-made SONAR. There is a large body of research that has studied and attempted to mimic this remarkable natural sonar system using various methodologies. In many studies, multiple microphones and time difference of arrival were used for bat ultrasonic wave measurements. In this work, a new method using spatial audio techniques is introduced for bat biosonar measurements and analyses. A custom-built tetrahedral soundfield microphone that captures high-frequency sound up to 80 kHz from all directions was developed to acquire bat ultrasonic echoes in Ambisonic B-format. The recorded sound was processed using the HARPEx (High Angular Resolution Planewave Expansion) technique that decodes the 1st order spherical harmonics of the soundfield at the microphone into two plane waves in each time-frequency bin. The use of the soundfield microphone and associated processing provides new tools for analysis of bat echoes from the perspective of the bat. This talk will present details of the hardware and software development along with experimental validation results.

Spatial Audio for Soundscape Design: Recording and Reproduction

With the advancement of spatial audio technologies, in both recording and reproduction, we are seeing more applications that incorporate 3D sound to create an immersive aural experience. Soundscape design and evaluation for urban planning can now tap into the extensive spatial audio tools for sound capture and 3D sound rendering over headphones and speaker arrays. In this paper, we outline a list of available state-of-the-art spatial audio recording techniques and devices, spatial audio physical and perceptual reproduction techniques, emerging spatial audio techniques for virtual and augmented reality, followed by a discussion on the degree of perceptual accuracy of recording and reproduction techniques in representing the acoustic environment.

Perceptual Spatial Audio Recording, Simulation, and Rendering: An overview of spatial-audio techniques based on psychoacoustics

Developments in immersive audio technologies have been evolving in two directions: physically motivated systems and perceptually motivated systems. Physically motivated techniques aim to reproduce a physically accurate approximation of desired sound fields by employing a very high equipment load and sophisticated, computationally intensive algorithms. Perceptually motivated techniques, however, aim to render only the perceptually relevant aspects of the sound scene by means of modest computational and equipment load. This article presents an overview of perceptually motivated techniques, with a focus on multichannel audio recording and reproduction, audio source and reflection culling, and artificial reverberators.

Off-Centre Localisation Performance of Ambisonics and HOA For Large and Small Loudspeaker Array Radii

Ambisonics and Higher Order Ambisonics (HOA) are scalable spatial audio techniques that attempt to present a sound scene to listeners over as large an area as possible. A localisation experiment was carried out to investigate the performance of a first and third order system at three listening positions one in the centre and two off-centre using a 5 m radius loudspeaker array. The results are briefly presented and compared to those of an earlier experiment on a 2.2 m loudspeaker array. In both experiments the off-centre listeners were placed such that the ratio of distance from the centre to the array radius was constant in both experiments. The test used a reverse target-pointer adjustment method to determine the error, both signed and absolute, for each combination of listening position and system. The results for both arrays were found to be very similar, suggesting that the relative amplitude of the loudspeakers, which were the same in both cases, was more dominant for localisation than the arrival time differences, which differed between array sizes.

The diffuse sound field in energetic analysis

Measuring the degree of diffuseness of a sound field is crucial in many modern parametric spatial audio techniques. In these applications, intensity-based diffuseness estimators are particularly convenient, as the sound intensity can also be used to obtain, e.g., the direction of arrival of the sound. This contribution reviews different diffuseness estimators comparing them under the conditions found in practice, i.e., with arrays of noisy microphones and with the expectation operators substituted by finite temporal averages. The estimators show a similar performance, however, each with specific advantages and disadvantages depending on the scenario. Furthermore, the paper derives an estimator and highlights the possibility of using spatial averaging to improve the temporal resolution of the estimates.