Andrew Schmeder

Efficient Directivity Pattern Control for Spherical Loudspeaker Arrays

With an appropriate control system, directivity pattern synthesis can be accomplished with spherical loudspeaker arrays, e.g. in the shape of Platonic solids or spheres. The application of such devices for the reproduction of natural or artificial directivity patterns poses a relatively young field of research in computer music and acoustic measurements. Using directivity measurements with microphones, the directivity patterns of the individual speakers on the array can be determined. Usually, the directivity of the whole array may be regarded as a linear combination of these patterns. In order to gain control, the measurement data of the linear system need to be inverted. Given L loudspeakers and M microphones, this inversion yields the desired control system, an expensive LxM multiple‐input‐multiple‐output (MIMO) filter. We introduce discrete spherical harmonics transform and decoder matrices to reduce the number of channels required for this control system, thus reducing the computational effort. Howev...

Room acoustics measurements with an approximately spherical source of 120 drivers

An approximately spherical source of 120 individually controlled drivers is used to perform impulse response measurements in a room with a 1.4 s reverberation time and a distinct echo. The signal to the drivers is processed to produce both omni‐directional and unidirectional patterns. The omni‐directional pattern is compared with measurements made with a traditional 12 sided source. The unidirectional patterns are measured both pointed towards and away from the listener position. Intelligibility metrics for the different directionalities and orientations are measured. The unidirectional pattern is aimed in different directions to minimally and maximally excite the distinct echo in the room, and locate its origin.

Synthesizing classic recording microphones characteristics using a spherical microphone array

Using spherical microphone arrays to form directed beams is becoming an important technology in sound field analysis, teleconferencing, and surveillance systems. Moreover, in scenarios for capturing musical content, the recording and post-production process could be simplified through flexible beamforming technology. Often, audio engineers favor the use of conventional recording microphones over spherical microphone arrays which might be due to the engineers preference for distinct spatial and timbral characteristics of different microphone types and brands. We present an approach to create beamforming pattern using a 144 channel spherical microphone array, which aims to match the distinct spatial and timbral characteristics of classic microphones. For this, we first measured the spatial and timbral characteristics of several classic microphones types as well as the characteristics of our spherical microphone array in an anechoic chamber. Using a regularized least-square approach, these data were then us...