Mikko-Ville Laitinen

Binaural reproduction for Directional Audio Coding

Directional audio coding (DirAC) is a recently proposed method for spatial sound reproduction. So far it has been used only in loud-speaker reproduction, and a method for headphone reproduction is presented in this article. In principle, the method uses virtual loud-speakers simulated with head related transfer functions (HRTFs), and head tracking. The method was evaluated subjectively, and the results are presented. The results show that a plausible spatial impression can be reproduced using the binaural realization of DirAC.

Directional audio coding - perception-based reproduction of spatial sound

Directional Audio Coding (DirAC) is a perceptually motivated technique for spatial audio processing. DirAC analyzes in short time windows the sound spectrum together with direction and diffuseness in frequency bands of human hearing, and uses this information in synthesis. It has applications in capturing, coding and resynthesis of spatial sound, in teleconferencing, in directional filtering, and in virtual auditory environments.

Parametric time-frequency representation of spatial sound in virtual worlds

Directional audio coding (DirAC) is a parametric time-frequency domain method for processing spatial audio based on psychophysical assumptions and on energetic analysis of the sound field. Methods to use DirAC in spatial sound synthesis for virtual worlds are presented in this article. Formal listening tests are used to show that DirAC can be used to position and to control the spatial extent of virtual sound sources with good audio quality. It is also shown that DirAC can be used to generate reverberation for N-channel horizontal listening with only two monophonic reverberators without a prominent loss in quality when compared with quality obtained with N-channel reverberators.

Converting 5.1 audio recordings to B-format for directional audio coding reproduction

A method to transform 5-channel surround sound signals to B-format is proposed, which provides unaltered spatial qualities when reproduced with directional audio coding (DirAC). The proposed method simulates anechoic B-format recording of the signals with two different virtual loudspeaker configurations, which are combined according to time-frequency analysis of diffuseness of the virtual sound field.

Controlling the perceived distance of an auditory object by manipulation of loudspeaker directivity

This work presents a method to control the perceived distance of an auditory object by changing the directivity pattern of a loudspeaker and consequently the direct-to-reverberant ratio at the listening spot. Control of the directivity pattern is achieved by beamforming using a compact multi-driver loudspeaker unit. A small-sized cubic array consisting of six drivers is assembled, and per driver beamforming filters are derived from directional measurements of the array. The proposed method is evaluated using formal listening tests. The results show that the perceived distance can be controlled effectively by directivity pattern modification.

Spatial audio coding with spaced microphone arrays for music recording and reproduction.

Spaced microphone arrays are commonly used in multichannel recording of music, due to their inherent quality of natural incoherence between the surround channels at reproduction, at the expense of accurate localization. Recent methods in parametric spatial audio coding, such as Directional Audio Coding, exploit coincident microphone patterns to extract directional information and reproduce it in a perceptually optimal way. In this study, we present how Directional Audio Coding can be adapted for spaced arrays, offering improved localization cues at reproduction, without compromising the qualities of the spaced microphone recording techniques. Examples are presented for some well-established array configurations.