Alexander Lindau

Minimum BRIR grid resolution for dynamic binaural synthesis

Binaural synthesis of acoustical environments is based on binaural room impulse responses (BRIRs) measured with a certain grid of spherical coordinates separated by angles of typically between 1° and 15°. The resulting spatial resolution defines the size of the BRIR database as well as the duration of its measurement. Perceptual evaluations of datasets with a different spatial resolution using HRTFs (anechoic case) have been reported from. Most of these studies use the localization performance of listeners as a criterion; a more sensitive measurement for slight degradations in audio quality can be expected from a criterion‐free comparison of datasets with different angular grids. Thus, to determine the minimum grid resolution required for dynamic binaural synthesis a listening test was performed. Following an adaptive 3AFC procedure, the spatial resolution of a recorded BRIR dataset was gradually lowered from a maximum of 1°/1° resolution until audible artefacts were introduced. This was done for a sound ...

Deriving content-specific measures of room acoustic perception using a binaural, nonlinear auditory model

Acousticians generally assess the acoustic qualities of a concert hall or any other room using impulse response-based measures such as the reverberation time, clarity index, and others. These parameters are used to predict perceptual attributes related to the acoustic qualities of the room. Various studies show that these physical measures are not able to predict the related perceptual attributes sufficiently well under all circumstances. In particular, it has been shown that physical measures are dependent on the state of occupation, are prone to exaggerated spatial fluctuation, and suffer from lacking discrimination regarding the kind of acoustic stimulus being presented. Accordingly, this paper proposes a method for the derivation of signal-based measures aiming at predicting aspects of room acoustic perception from content specific signal representations produced by a binaural, nonlinear model of the human auditory system. Listening tests were performed to test the proposed auditory parameters for both speech and music. The results look promising; the parameters correlate with their corresponding perceptual attributes in most cases.

Audibility and Interpolation of Head-Above-Torso Orientation in Binaural Technology

Head-related transfer functions (HRTFs) incorporate fundamental cues required for human spatial hearing and are often applied to auralize results obtained from room acoustic simulations. HRTFs are typically available for various directions of sound incidence and a fixed head-above-torso orientation (HATO). If-in interactive auralizations-HRTFs are exchanged according to the head rotations of a listener, the auralization result most often corresponds to a listener turning head and torso simultaneously, while-in reality-listeners usually turn their head independently above a fixed torso. In the present study, we show that accounting for HATO produces clearly audible differences, thereby suggesting the relevance of correct HATO when aiming at perceptually transparent binaural synthesis. Furthermore, we addressed the efficient representation of variable HATO in interactive acoustic simulations using spatial interpolation. Hereby, we evaluated two different approaches: interpolating between HRTFs with identical torso-to-source but different head-to-source orientations (head interpolation) and interpolating between HRTFs with the same head-to-source but different torso-to-source orientations (torso interpolation). Torso interpolation turned out to be more robust against increasing interpolation step width. In this case the median threshold of audibility for the head-above-torso resolution was about 25 degrees, whereas with head interpolation the threshold was about 10 degrees. Additionally, we tested a non-interpolation approach (nearest neighbor) as a suitable means for mobile applications with limited computational capacities.

On the authenticity of individual dynamic binaural synthesis

A simulation that is perceptually indistinguishable from the corresponding real sound field could be termed authentic. Using binaural technology, such a simulation would theoretically be achieved by reconstructing the sound pressure at a listeners ears. However, inevitable errors in the measurement, rendering, and reproduction introduce audible degradations, as it has been demonstrated in previous studies for anechoic environments and static binaural simulations (fixed head orientation). The current study investigated the authenticity of individual dynamic binaural simulations for three different acoustic environments (anechoic, dry, wet) using a highly sensitive listening test design. The results show that about half of the participants failed to reliably detect any differences for a speech stimulus, whereas all participants were able to do so for pulsed pink noise. Higher detection rates were observed in the anechoic condition, compared to the reverberant spaces, while the source position had no significant effect. It is concluded that the authenticity mainly depends on how comprehensive the spectral cues are provided by the audio content, and the amount of reverberation, whereas the source position plays a minor role. This is confirmed by a broad qualitative evaluation, suggesting that remaining differences mainly affect the tone color rather than the spatial, temporal or dynamical qualities.

A Database of Anechoic Microphone Array Measurements of Musical Instruments

Violin (classical) Violin_historical 430 Hz G3-C7 G3-C7 Normal of the soundboard aiming at Mic#25, Scroll aiming at between Mic#02 and Mic#03 Daniel Deuter 200905-18 14:15 15:15 Instrument: Neil Kristóv Értz (1998, rev. 2003), Copy of Guaneri; Bow: Violin Bow (50 g), René Groppe (Metz, 1997), Copy of baroque model (17th century); Strings: E String: Catgut (Damian Dlugolecki, 0.62 mm); A String: Catgut (Nicholas Baldock, Kathedrale Strings, 0.74 mm); D String: Catgut (+0.25 mm Silver, 1.12mm, Nicholas Baldock, LuxLine); G String: Catgut, Silver, diameter unknown

Efficiency of two‐dimensional interpolation algorithms for high‐quality dynamic binaural synthesis

Binaural synthesis of acoustical environments is based on binaural room impulse responses (BRIRs) measured with an angular resolution of typically between 1° and 15°. Considering the size of the resulting BRIR database used for auralization and the long measurement duration for its acquisition, it is reasonable to use interpolation from a lower resolution BRIR grid. Based on a mathematical formulation of the interpolation problem for BRIRs, a set of different solutions for two‐dimensional spaces is described and compared with regard to efficiency and real time performance. In order to evaluate the degradation introduced by interpolation, different methods have been implemented and applied to a HRTF and a BRIR database measured in two degrees of freedom with 1°/1° horizontal/vertical resolution. These are bilinear interpolation (i.e. nearest neighbour, inverse distance weighting), spherical spline interpolation, wavelet interpolation, and interpolation based on principal component analysis (PCA). A listeni...