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Ambisonics has enjoyed a recent resurgence in popularity due to virtual reality applications, where Ambisonic audio is presented to the user binaurally in conjunction with a head-mounted display. In this scenario however, it is imperative to maximise the coherence between audio in the frontal direction and visuals in order to maintain immersion.Ambisonic reproduction can theoretically be perfect in the centre of the loudspeaker array for frequencies up to the `spatial aliasing frequency', $f_{alias}$. At frequencies above $f_{alias}$ however, the limited spatial accuracy of reproducing a physical sound field with a finite number of transducers causes artefacts such as localisation blur, reduced lateralisation and comb filtering. One approach for improving spectral reproduction of binaural Ambisonic rendering is diffuse-field equalisation. In a previous study, the authors applied this technique to virtual loudspeaker binaural Ambisonic decoders, which improved both the spectral response over the sphere and predicted median plane elevation localisation. However, there still exists a perceivable difference in timbre between diffuse-field equalised binaural Ambisonic rendering and HRTF convolution. By altering the diffuse-field equalisation method by concentrating the equalisation for one specific direction (for the virtual reality application this direction is the front), it is possible to create a hybrid of free-field and diffuse-field equalisation such that frontal reproduction becomes more accurate, at the expense of other directions. This is referred to as directional bias equalisation (DBE) and is a two-stage equalisation process. The first obtains a frontal directionally biased spherical field response and equalises it, and the second re-equalises this response for the ideal corresponding frontal response such that an infinite directional bias will produce frontal Ambisonic audio equivalent to frontal HRTF convolution. DBE is a pre-processing stage that can be implemented offline. Increasing the frontal bias factor (represented in this paper using the letter $\kappa$) improves spectral reproduction of frontal sounds to a greater extent, though this comes at the expense of spectral accuracy at other directions. This paper presents the results of a perceptual listening test that attempts to determine the optimal bias factor for an appropriate trade off between improved frontal fidelity and reduced lateral fidelity. The test follows the multiple stimulus with hidden reference and anchors (MUSHRA) paradigm, ITU-R BS.1534-3. Tests are conducted in a quiet listening room using a single set of Sennheiser HD~650 circum-aural headphones and an Apple Macbook Pro with a Fireface UCX audio interface, which has software controlled input and output levels. Headphones are equalised from the RMS average of 11 impulse response measurements, with 1 octave band smoothing in the inverse filter. All audio is 24-bit depth and 48~kHz sample rate. Listening tests are conducted using first, third and fifth order Ambisonics, with loudspeaker configurations comprising 6, 26 and 50 loudspeakers respectively, arranged in Lebedev grids. Test conditions are as follows:\begin{itemize} \item HRTF convolution (reference) \item Standard Ambisonic \item DBE Ambisonic with $\kappa = 1$ \item DBE Ambisonic with $\kappa = 3$ \item DBE Ambisonic with $\kappa = 5$ \item DBE Ambisonic with $\kappa = 9$ \item DBE Ambisonic with $\kappa = 17$ \item DBE Ambisonic with $\kappa = 33$\end{itemize}Additional stimuli are a low and mid anchor for the simple scenes, comprised of the HRTF reference low-passed at 3.5~kHz and 7~kHz respectively, and a zeroth order Ambisonic render for the complex scenes. Two simple and one complex scenes are used. The simple scenes comprise of a single pink noise source. The first is panned directly in front of the listener at ($\theta,\phi$) = ($0^\circ,0^\circ$), and the second is panned directly to the left of the listener at ($\theta,\phi$) = ($90^\circ,0^\circ$). The complex scene is simulated by mixing a frontal pink noise and a diffuse soundscape. The noise burst consists of 0.5s burst and 0.5s of silence. The diffuse soundscape is synthesised from 24 decorrelated monophonic sound scene recordings of a train station. The 24 sources are panned to the vertices of a 24 pt. T-design quadrature, to ensure minimal overlap between virtual loudspeaker positions in the binaural decoders and the sound sources in the complex scene. The frontal noise is 3~dB~RMS louder than the diffuse soundscape. Results are analysed using non-parametric statistics and discussed in the full manuscript. The conclusion suggests the perceptually optimal bias factor for improved frontal spectral fidelity with minimal perceived lateral degradation for virtual loudspeaker binaural Ambisonic rendering.

Virtual Reality (VR) has been an active area of research in the development of interactive interventions for individuals with autism spectrum disorder (ASD) for over two decades. These immersive environments create a safe platform in which therapy can address the core symptoms associated with this condition. Recent advancements in spatial audio rendering techniques for VR now allow for the creation of realistic audio environments that accurately match their visual counterparts. However, reported auditory processing impairments associated with autism may affect how an individual interacts with their virtual therapy application. This study aims to investigate if these difficulties in processing audio information would directly impact how individuals with autism interact with a presented virtual spatial audio environment. Two experiments were conducted with participants diagnosed with ASD (n = 29) that compared: (1) behavioral reaction between spatialized and non-spatialized audio; and (2) the effect of background noise on participant interaction. Participants listening to binaural-based spatial audio showed higher spatial attention towards target auditory events. In addition, the amount of competing background audio was reported to influence spatial attention and interaction. These findings suggest that despite associated sensory processing difficulties, those with ASD can correctly decode the auditory cues simulated in current spatial audio rendering techniques.

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.

Binaural Ambisonic rendering is widely used in immersive applications such as virtual reality due to its sound field rotation capabilities. Binaural Ambisonic reproduction can theoretically replicate the original sound field exactly for frequencies up to what is commonly referred to as the `spatial aliasing frequency', $f_{alias}$. At frequencies above $f_{alias}$ however, reproduction can become inaccurate due to the limited spatial accuracy of reproducing a physical sound field with a finite number of transducers, which in practice causes localisation blur, reduced lateralisation and comb filtering spectral artefacts. The standard approach to improving Ambisonic reproduction is to increase the order of Ambisonics, which allows for exact sound field reproduction up to a higher $f_{alias}$, though at the expense of more channels for storage, more microphone capsules for recording, and more convolutions in binaural reproduction. It is therefore highly desirable to explore alternative methods of improving low-order Ambisonic rendering. One common practice is to employ a dual-band decoder with basic Ambisonic decoding at low frequencies and Max $r_E$ channel weighting above $f_{alias}$, which improves spectral, localisation and lateralisation reproduction. Virtual loudspeaker binaural Ambisonic decoders can be made by multiplying each loudspeaker's head-related impulse responses (HRIRs) with the decode matrix coefficients and summing the resulting spherical harmonic (SH) channels. This approach allows for dual-band decoding and loudspeaker configurations with more loudspeakers than SH channels whilst minimising the required number of convolutions. Binaural Ambisonic reproduction using the virtual loudspeaker approach is then achieved by a summation of direct convolution of each SH channel of the encoded signal with the corresponding SH channel of the binaural decoder. This paper presents the method and results of a perceptual comparison of state-of-the-art pre-processing techniques for virtual loudspeaker binaural Ambisonic rendering. By implementing these pre-processing techniques in the HRTFs used in the virtual loudspeaker binaural rendering stage, improvements can be made to the rendering. All pre-processing techniques are implemented offline, such that the resulting binaural decoders are of the same size and require the same number of real-time convolutions.The three pre-processing techniques investigated in this study are:\begin{itemize} \item Diffuse-field Equalisation (DFE) \item Ambisonic Interaural Level Difference Optimisation (AIO) \item Time Alignment (TA) \end{itemize}DFE is the removal of direction-independent spectral artefacts in the Ambisonic diffuse-field. AIO augments the gains of the left and right virtual loudspeaker HRTF signals above $f_{alias}$ such that Ambisonic renders produce more accurate interaural level differences (ILDs). TA is the removal of interaural time differences (ITDs) between the HRTFs above $f_{alias}$ to reduce high frequency comb filtering effects.The test follows the multiple stimulus with hidden reference and anchors (MUSHRA) paradigm, ITU-R BS.1534-3. Tests are conducted in a quiet listening room using a single set of Sennheiser HD~650 circum-aural headphones and an Apple Macbook Pro with a Fireface UCX audio interface, which has software controlled input and output levels. Headphones are equalised from the RMS average of 11 impulse response measurements, with 1 octave band smoothing in the inverse filter. All audio is 24-bit depth and 48~kHz sample rate. Listening tests are conducted using first, third and fifth order Ambisonics, with respective loudspeaker configurations comprising 6, 26 and 50 loudspeakers, arranged in Lebedev grids. The different test conditions are made up of various combinations of the three pre-processing techniques. The test conditions are as follows:\begin{enumerate} \item HRTF convolution (reference) \item Standard Ambisonic (dual band) \item Ambisonic with DFE (dual band) \item Ambisonic with AIO (dual band) \item Ambisonic with AIO \ DFE (dual band) \item Ambisonic with TA \ DFE (basic) \item Ambisonic with TA \ AIO \ DFE (basic) \item Ambisonic with TA \ AIO \ DFE (dual band)\end{enumerate}The stimuli are synthesised complex acoustic scenes, defined in this paper as an acoustic scene with multiple sources. The synthesised complex scene used in this paper is composed from 24 freely available stems of an orchestra. Instruments are isolated and empirically matched in loudness. The orchestral stems are panned to the vertices of a 24 pt. T-design arrangement, to ensure minimal overlap between virtual loudspeaker positions in the binaural decoders and the sound sources in the complex scene. Synthesising complex scenes in this way allows for an explicit target reference stimulus - in this case a direct HRTF convolved render. If the Ambisonic stimuli are perfectly reconstructed, they will be equivalent to the reference stimulus. Results are analysed using non-parametric statistics and discussed in the full manuscript. The conclusion suggests the perceptually preferred pre-processing algorithms for virtual loudspeaker binaural Ambisonic rendering./latex

Individuals with autism spectrum disorder (ASD) who exhibit developmental lim- itations in social-emotional interaction and communication, are widely reported to respond positively to music therapy interventions that incorporate active and im- provisational techniques. The fundamental elements of music have been shown to bypass both cognitive and language impairments to help facilitate communication skills, form social relationships and promote cognitive progression. In recent years, computer technologies such as mobile devices and interactive motion capture systems are being developed to provide new approaches to music interaction. When included into new or existing music interventions, digital technology can enhance the music playing experience and motivate children to interact differently with their environ- ment through providing novel and engaging approaches to music interaction and creativity. This review highlights the core symptoms of ASD and presents evidence that supports the use of music therapy techniques within the autistic population, underpinned by neurological studies reporting on benefits of musical intervention. Further to this, it is explained how new technologies such as mobile devices and multi-sensory computer systems can move beyond traditional music instruments to add additional dimensions to music therapy sessions. Finally suggestions of future research are made alongside considerations in designing new and novel auditory interventions.

As binaural audio continues to permeate immersive technologies, it is vital to develop a detailed understanding of the perceptual relevance of HRTFs. Previous research has explored the benefit of individual HRTFs with respect to localisation. However, localisation is only one metric with which it is possible to rate spatial audio. This paper evaluates the perceived timbral and spatial characteristics of both individual and non-individual HRTFs and compares the results to overall preference. To that end, the measurement and evaluation of a high-resolution multi-environment binaural Impulse Response database is presented for 20 subjects, including the KU100 and KEMAR binaural mannequins. Post-processing techniques, including low frequency compensation and diffuse field equalisation are discussed in relation to the 8802 unique HRTFs measured for each mannequin and 2818/2114 HRTFs measured for each human. Listening test results indicate that particular HRTF sets are preferred more generally by subjects over their own individual measurements.

Audio Description for film and television is a pre-recorded track that uses verbal descriptions to provide information on visual aspects of a film or TV programme. In the UK it is currently the only accessibility strategy available for visually impaired audiences and although it provides access to a large number of people, its shortcomings also fail to engage others in audiovisual experiences. The Enhancing Audio Description project explores how digital audio technologies can be applied to the creation of alternatives to Audio Description with the aim of personalising access strategies. Such personalisation would allow users to select the method utilised to access audiovisual experiences, by having choices that include traditional forms of accessibility as well as sound design based methods. The present article analyses the results of a survey and focus groups in which visually impaired participants discussed the advantages and disadvantages of AD and it demonstrates not only the diversity of experiences and needs of visually impaired groups but also their eagerness for change.

Timbre is a crucial element of believable and natural binaural synthesis. This paper presents a method for diffuse-field equalisation of first-order Ambisonic binaural rendering, aiming to address the timbral disparity that exists between Ambisonic rendering and head related transfer function (HRTF) convolution, as well as between different Ambisonic loudspeaker configurations. The presented work is then evaluated through listening tests, and results indicate diffuse-field equalisation is effective in improving timbral consistency.