I've got some code which creates a virtual impulse response of a room with arbitrary dimensions. I want to know, how can I add more than one absorption coefficient into it?
function h = rir(fs, mic, n, r, rm, src) % RIR Room Impulse Response. % [h] = RIR(FS, MIC, N, R, RM, SRC) performs a room impulse % response calculation by means of the mirror image method. % % FS = sample rate. % MIC = row vector giving the x,y,z coordinates of % the microphone. % N = The program will account for (2*N+1)^3 virtual sources % R = reflection coefficient for the walls, in general -1<R<1. % RM = row vector giving the dimensions of the room. % SRC = row vector giving the x,y,z coordinates of % the sound source. % % EXAMPLE: % % >>fs=44100; % >>mic=[19 18 1.6]; % >>n=12; % >>r=0.3; % >>rm=[20 19 21]; % >>src=[5 2 1]; % >>h=rir(fs, mic, n, r, rm, src); % % NOTES: % % 1) All distances are in meters. % 2) The output is scaled such that the largest value of the % absolute value of the output vector is equal to one. % 3) To implement this filter, you will need to do a fast % convolution. The program FCONV.m will do this. It can be % found on the Mathworks File Exchange at % www.mathworks.com/matlabcentral/fileexchange/. It can also % be found at http://www.sgm-audio.com/research/rir/fconv.m % 4) A paper has been written on this model. It is available at: % http://www.sgm-audio.com/research/rir/rir.html % % %Version 3.4.2 %Copyright 2003 Stephen G. McGovern %Some of the following comments are references to equations the my paper. nn = -n:1:n; % Index for the sequence rms = nn+0.5-0.5*(-1).^nn; % Part of equations 2,3,& 4 srcs = (-1).^(nn); % part of equations 2,3,& 4 xi = srcs*src(1)+rms*rm(1)-mic(1); % Equation 2 yj = srcs*src(2)+rms*rm(2)-mic(2); % Equation 3 zk = srcs*src(3)+rms*rm(3)-mic(3); % Equation 4 [i, j, k] = meshgrid(xi, yj, zk); % convert vectors to 3D matrices d = sqrt(i.^2+j.^2+k.^2); % Equation 5 time = round(fs*d/343)+1; % Similar to Equation 6 [e, f, g] = meshgrid(nn, nn, nn); % convert vectors to 3D matrices c = r.^(abs(e)+abs(f)+abs(g)); % Equation 9 e = c./d; % Equivalent to Equation 10 h = full(sparse(time(:), 1, e(:))); % Equivalent to equation 11 h = h/max(abs(h)); % Scale output end
At the moment, the variable 'r' is the absorption coefficient for the whole room. But for the assignment I'm doing, I'm taking the RT60 of a theoretical, cuboid room that has various absorption coefficients for various surfaces.
FYI, I've looked for the paper Stephen McGovern mentions. I've found a couple of copies on archive.org but none with images! Which is kind of useless because all the images have the relevant equations.