
Reverb Filter Generator
Type : FIR References : Posted by Stephen McGovern
Notes : This is a MATLAB function that makes a rough calculation of a room's impulse response. The output can then be convolved with an audio clip to produce good and realistic sounding reverb. I have written a paper discussing the theory used by this algorithm. It is available at http://stevem.us/rir.html.
NOTES:
1) Large values of N will use large amounts of memory.
2) The output is normalized to the largest value of the
output.
Code : 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
% 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 www.2pi.us/code/fconv.m
% 4) A paper has been written on this model. It is available at:
% www.2pi.us/rir.html
%
%
%Version 3.4.1
%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+0.50.5*(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 
Comments
Added on : 10/01/05 by thaddy[ AT ]thaddy[ DOT ]com Comment : Can someone put this is C code? I have no problems with the fft/ifft parts and the convolution itself, but this gets me stuck:
// from the Fconv.m file in the article
1:1:Ym
Added on : 12/05/05 by ibanez82[ AT ]katamail[ DOT ]com Comment : Fate una versione in C!!!!

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