Contact
Jacob Hollebon, VAAE Team, ISVR, University of Southampton
J.Hollebon@soton.ac.uk
https://www.southampton.ac.uk/vaae/about/staff/jh4g17.page
 
Citation
Hollebon, J. And Fazi, Filippo Maria: “Experimental Study of Various Methods for Low Frequency Spatial Audio Reproduction Over Loudspeakers” Immersive and 3D Audio (I3DA) International Conference, 2021
 
Introduction
This repository is a database of anechoic B-format impulse responses for a source positioned around an Eigenmike EM32 microphone in the horizontal plane.
The measurements were performed by Jacob Hollebon, in the large anechoic chamber at the ISVR in Jan 2021 as part of his PhD thesis.
The final measurements present the impulse responses of a loudspeaker positioned over 360 horizontal positions in a 1 degree resolution, to 4th order Ambisonic B-format using ACN channel ordering and SN3D normalisation.
The dataset is made freely available under a Creative Commons CC BY License. Please reference the accommodating paper when you use this data.

Experimental Setup
The Eigenmike is a 32 channel spherical microphone array. A Generic 8020C loudspeaker was positioned at varying radii of 1m, 2m and 3m away from the Eigenmike. The centre of the Eigenmike was aligned with the top of the Genelec woofer. The Eigenmike was situated on a turntable and rotated through 360 degrees, measuring every 1 degree using a sine sweep method with 10s sweeps from 1Hz to 24kHz at a sampling frequency of 48kHz. The raw microphone signals were then deconvolved with the corresponding inverse filter to give a set of impulse responses from the loudspeaker to each given microphone.

Post-Processing
For full details of the post-processing, please see the paper that accompanies this dataset. An overview is given below.

Frequency Dependent Windowing was applied to remove the effect of any floor tiles that were not able to be removed from the large anechoic chamber, thus a short window was used at high frequencies and a longer window at low frequencies to ensure the loudspeaker response is fully retained in this region.

Next, to convert the impulse responses from loudspeaker to microphone into a set of loudspeaker to B-Format impulse responses, the Eigenmike VST plugin was utilised to perform the conversion. ACN channel numbering and SN3D normalisation was used.

Finally, onset-based time alignment was applied to remove any sources of error due to changes in distance between the microphone and the loudspeaker (for example, due to the microphone not being completely centred on the turntable). This was performed using the W channels for each measurement direction, calculating the time of arrivals and then the corresponding delay when compared to a measurement direction of 0 degrees. These delays were then removed using fractional delay filters. The delay was assumed to be constant factor for each given measurement direction. Thus the delay was just calculated from the W channel then removed from all B format channels for each given direction.

Data Description
The final data is made available as numpy (.npy) files for use within Python.
There are three different radii - 1m, 2m and 3m.
The impulse responses (IRs), transfer functions (TFs) and the Nfft value used in the Fourier transform are saved as separate files with the following naming convention

‘distance_datatype.npy’

For example the IRs for the 3m radius would be ‘3m_IRs.npy’.

The impulse responses and transfer functions are an array od size ‘channels x measurement directions x samples/frequency’. 

License
CC-BY