Attached is some Matlab code written by Keansub Lee in my lab when we were looking at making "personal audio lifelog" recordings unintelligible while preserving the statistics needed for classifying environment and speakers. It chops the sound into overlapping 200ms windows and permutes them within a 1 second radius. Basic usage is just y = scrambling(d,sr); where d is the input audio and sr is the sampling rate. See comments in the file for changing the parameters (window length, overlap, scramble radius etc.). Also attached are a brief speech sound before and after scrambling. Apologies to digest readers who will probably see a great deal of meaningless ascii. DAn.
function y = scrambling(x, sr, h, w, wintype, s) % % x is a input signal and sr is samplingrate. % Using w-points[200ms] windows every h-points[100ms] over s-points[1 sec] radius, % scramble the input signal. % Make sure that the length of window should be smaller than 2*(frame's length) % % For example, % [x,sr]= wavread('mdwh0_sx305.wav'); % h = sr*.1; % w = h*2; % wintype = 'sinewin'; % s = sr; % y = scrambling(x, sr, h, w, wintype, s); % 2004-10-14 kslee@xxxxxxxxxxxxxxx if nargin < 3 h = sr*0.1; % 100ms, frame length end if nargin < 4 w = 2*h; % 200ms, window length end if nargin < 5 wintype = 'sinewin'; % window type end if nargin < 6 s = sr; % 1s, segments length end switch wintype case 'sinewin' wt = sin(pi*([0:(w-1)]' + 0.5)/w);; case 'hanningwin' wt = hanning(w); end if (size(x,1) == 1) x = x'; % Convert X from row to column end %x= x(1:sr*3); % the points of input signal npts = length(x); % the total number of segments within input signal nsegs = floor(npts/s); % the total number of frames within each segment nhops = floor(s/h); y = ; for seg = 1:nsegs % Extract segment of signal xx = x((seg - 1)*s + [1:s]); % points to be scrambled and remained xxs = xx(1:nhops*h,1); xxr = xx((nhops*h + 1):end,1); % Pad x with zeros to extract complete w-length windows from it xxs = [zeros((w-h)/2,1);xxs;zeros((w-h/2),1)]; % save the scrambled signal yys = zeros((nhops+1)*h,1); % random permutation nrands = randperm(nhops); for hop = 1:nhops % Break the signal into w-length windows xxsw = xxs((nrands(hop) - 1)*h + [1:w]); % Apply window wxxsw = xxsw .* wt; % reverse and save it % yys((hop - 1)*h + [1:w],1) = yys((hop - 1)*h + [1:w],1) + wxxsw([end:-1:1]); yys((hop - 1)*h + [1:w],1) = yys((hop - 1)*h + [1:w],1) + wxxsw; end % trancate the # of zeros padding points to have a same size of original yy = [yys(h/2+1:end-h/2,1);xxr]; y = [y;yy]; end
Description: Wave audio
Description: Wave audio