b@2: function stripzeros(foldername)
b@2: % STRIPZEROS strips off an array of samples that equal zero at the 
b@2: % beginning and end of an audio file. 
b@2: %
b@2: % by Brecht De Man at Centre for Digital Music on 17 November 2014
b@2: 
b@2:     tic;                                % start measuring time
b@2:     list = dir([foldername '/*.wav']);  % get names of files
b@2: 
b@2:     % remove hidden files from list
b@2:     % see http://www.mathworks.co.uk/matlabcentral/newsreader/view_thread/258220
b@2:     for k = length(list):-1:1
b@2:         fname = list(k).name;
b@2:         if fname(1) == '.'
b@2:             list(k) = [ ];
b@2:         end
b@2:     end
b@2: 
b@2:     for i = 1:length(list) % go over each file in the folder
b@2:         [audio, fs] = audioread([foldername '/' list(i).name]);
b@2: 
b@2:         numSamples  = size(audio,1);
b@2:         numChannels = size(audio,2);
b@2:         bitDepth    = 24; % not automated here
b@2:         startIndex  = zeros(numChannels, 1);
b@2:         stopIndex   = zeros(numChannels, 1);
b@2: 
b@2:         % first and last non-zero elements (for all channels)
b@2:         for channel = 1:numChannels
b@2:             % ? more efficient way to find first and last non-zero sample?
b@2:             indexOfNonZeroSamples = find(audio(:,channel)); % returns indices non-zero elements
b@2:             startIndex(channel) = min(indexOfNonZeroSamples);
b@2:             stopIndex(channel)  = max(indexOfNonZeroSamples);
b@2:         end
b@2: 
b@2:         start = max(startIndex);
b@2:         stop  = min(stopIndex);
b@2: 
b@2:         % if startIndex and stopIndex are both equal to first and last sample: 
b@2:         % do nothing.
b@2:         % else: 
b@2:         if start>1 || stop<numSamples
b@2:             audiowrite([foldername '/' list(i).name], audio([start:stop], :), ...
b@2:                 fs, 'BitsPerSample', bitDepth);
b@11:             % debugging/monitoring: 
b@11:             startCrop = (start-1)/fs; %
b@11:             stopCrop  = (size(audio,1)-stop)/fs;
b@11:             disp([num2str(startCrop) 's (start) / ' num2str(stopCrop) 's (end) stripped off ' list(i).name]);
b@11:         else
b@11:             disp(['Nothing stripped off ' list(i).name]);
b@2:         end
b@2: 
b@11:         
b@2:     end
b@2: 
b@2:     elapsedTime = toc;  % stop measuring time
b@2:     disp(['stripzeros took ' num2str(elapsedTime) ' seconds to strip zeros off the files in folder ' ...
b@2:     foldername]);
b@2: 
b@2: end