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HO-SIRR

Higher-order Spatial Impulse Response Rendering (HO-SIRR) is a rendering method, which can synthesise output loudspeaker array room impulse responses (RIRs) using input spherical harmonic (Ambisonic/B-Format) RIRs of arbitrary order. The method makes assumptions regarding the composition of the sound-field and extracts spatial parameters over time, which allows it to map the input to the output in an adaptive and more informed manner; when compared to linear methods such as Ambisonics.

The idea is that you then convolve a monophonic source with this loudspeaker array RIR, and it will be reproduced and exhibit all of the spatial characteristics of the captured space.

(Please note that the code is currently a "work in progress". Therefore, feedback is most welcome! :-)

The above image depicts energy spectrograms of a 64-channel loudspeaker array RIR, rendered using different methods/configurations using the included 'plot_mch_energy.m' script. Here, it can be observed that the renderings using HO-SIRR more closely resembles the reference with increasing input order. It also performs visibly better than Ambisonics (MMD).

Getting Started

The code is reliant on the following Matlab libraries:

The HO-SIRR script may be configured, for example, as:

pars.fs = 48e3; 
pars.ls_dirs_deg = ???; % your loudspeaker array directions, [azi elev], in degrees

% Specify STFT windowing size in samples (note that HO-SIRR uses 50% window overlap)
pars.multires_winsize = [128]; 
pars.multires_xovers = [];
% OR: Specify windowing sizes for a multi-resolution STFT, for example:
% (512 up to 500Hz, then 128 up to 2kHz, then 64 above 2kHz)
%pars.multires_winsize = [512 128 64]; 
%pars.multires_xovers = [500 2e3]; 

% Diffuse rendering parameters
pars.RENDER_DIFFUSE = 1;          % 0: disable diffuse rendering, 1: enable
pars.decorrelationType = 'noise'; % {'phase','noise'}, decorrelation via convolution with 'noise', or by randomising the 'phase'
pars.BROADBAND_DIFFUSENESS = 1;   % 0: bin-wise estimation of diffuseness, 1: estimate diffuseness using broad-band intensity (<=maxDiffFreq_Hz)
pars.maxDiffFreq_Hz = 3e3;        % frequency up to which to estimate the diffuseness parameter 
pars.alpha_diff = 0.5;            % diffuseness averaging coefficient (one-pole filter)

% Optionally, the highest peak of the response may be isolated and panned 
% using a broad-band DoA estimate, which can reduce timbral colourations
% in some cases
pars.BROADBAND_FIRST_PEAK = 1;    % 0: disabled, 1: enabled

The input Ambisonic RIR may then be rendered for your loudspeaker set-up as:

pars.chOrdering = 'ACN'; % 'ACN', or 'WXYZ'  
pars.normScheme = 'N3D'; % 'N3D', or 'SN3D'
shir = audioread( ??? ) % load your input spherical harmonic RIR (of arbitrary order)
[lsir, lsir_ndiff, lsir_diff, pars, analysis] = HOSIRR(shir, pars);
% lsir       - output loudspeaker impulse responses
% lsir_ndiff - output loudspeaker impulse responses, direct stream only
% lsir_diff  - output loudspeaker impulse responses, diffuse stream only
% pars       - output parameters
% analysis   - analysed parameters stored during rendering

Then simply convolve this loudspeaker RIR (lsir) with a monophonic input stimulus, in order to reproduce it over your loudspeaker array and have it exhibit the spatial characteristics of the captured room.

Developers

License

This code is provided under the BSD 3-clause license.

References

[1] McCormack, L., Pulkki, V., Politis, A., Scheuregger, O. and Marschall, M., (2020). "Higher-Order Spatial Impulse Response Rendering: Investigating the Perceived Effects of Spherical Order, Dedicated Diffuse Rendering, and Frequency Resolution". Journal of the Audio Engineering Society, 68(5), pp.338-354.

[2] McCormack, L., Politis, A., Scheuregger, O., and Pulkki, V. (2019). "Higher-order processing of spatial impulse responses". In Proceedings of the 23rd International Congress on Acoustics, 9--13 September 2019 in Aachen, Germany.

[3] Politis, A. and Pulkki, V., 2016. "Acoustic intensity, energy-density and diffuseness estimation in a directionally-constrained region". arXiv preprint arXiv:1609.03409.

[4] Merimaa, J. and Pulkki, V., 2005. "Spatial impulse response rendering I: Analysis and synthesis". Journal of the Audio Engineering Society, 53(12), pp.1115-1127.

[5] Pulkki, V. and Merimaa, J., 2006. "Spatial impulse response rendering II: Reproduction of diffuse sound and listening tests". Journal of the Audio Engineering Society, 54(1/2), pp.3-20.

[6] Favrot, S. and Buchholz, J.M., 2010. "LoRA: A loudspeaker-based room auralization system. Acta Acustica united with Acustica", 96(2), pp.364-375.