Trying to convert whole folder into spectrograms

Hi, I have a local folder of .wav files that Id like to convert to spectrograms (.png) in another local folder. so I can use it to train my CNN model. This is what I have but it's not working. Also gave no errors. Help please!!

folder = uigetdir(pwd,'*insert source folder path name here*');

filelist = dir(fullfile(folder, '*.wav')); %get list of all wav files in the folder

for fileidx = 1:numel(filelist)

[audioIn,fs] = audioread({filelist.name});

S = melSpectrogram(audioIn,fs);

save('*insert destination folder path name here*','Cough1.png','-png');

end

Answer 1

[jibrahim]

Hi Justine, consider using an audioDatastore to do this. then you don't have to write the for loop. for example:

% This audioDatastore will point to all audio files in folder and its
% subfolders
ads = audioDatastore(folder,IncludeSubfolders=true);

% Write my images here
outputLocation = fullfile(tempdir,"mySpectrograms");

% Create PNGs for all audio files.
writeall(ads,outputLocation,WriteFcn=@myCustomWriter);

function myCustomWriter(audioIn,writeInfo,~)
% Get the sample rate of the audio file
fs = writeInfo.ReadInfo.SampleRate;
% Extract Mel spectrogram
S = melSpectrogram(audioIn,fs);
% Form image name
imagename = strrep(writeInfo.SuggestedOutputName,".wav",".png");
% Save image
imwrite(S(:,:,1),imagename);
end

[Justine Hughes]

Thank you, so it saves well. However, the spectrograms don't show up at all :(

They're just black images. Perhaps it has something to do with the fs?

[jibrahim]

Hi Justine,

How about this?

% This audioDatastore will point to all audio files in folder and its
% subfolders
ads = audioDatastore(folder,IncludeSubfolders=true);
% Write my images here
outputLocation = fullfile(tempdir,"mySpectrograms");
% Create PNGs for all audio files.
writeall(ads,outputLocation,WriteFcn=@myCustomWriter);


function myCustomWriter(audioIn,writeInfo,~)
% Get the sample rate of the audio file
fs = writeInfo.ReadInfo.SampleRate;
% Extract Mel spectrogram. This generates a plot.
melSpectrogram(audioIn,fs);
% Form image name
imagename = strrep(writeInfo.SuggestedOutputName,".wav",".png");

% Save the figure as an image
saveas(gcf,imagename);

end

[Justine Hughes]

Okay so when I used imagename as a variable it didnt work but when I put the strrep function to replace imagename in saveas, it worked :) thank you very much!

Answer 2

[Rik]

You are inserting all files at once, instead of indexing into the filelist array.

If you want want to store an image you need to use imwrite. Look up the documentation to see several examples. I would suggest generating the file name of the png with fullfile, using filelist(n).folder.

[Justine Hughes]

I updated it with imwrite and tried to index filelist but perhaps I misunderstood.

Im kind of inexperienced with matlab, could you explain this please?

for fileidx = 1:numel(filelist)
    [audioIn,fs] = audioread(filelist.name(fileidx));    %this line gives the error
    S = melSpectrogram(audioIn,fs);
    filename = sprintf('Cough%d.png',fileidx);
    imagename = [savefolder,'\Cough_',num2str(fileidx),'.png'];
    imwrite(S,imagename); %save image as png
end

[Rik]

You're indexing the field, not the struct.

for fileidx = 1:numel(filelist)
    [audioIn,fs] = audioread(filelist(fileidx).name);
    S = melSpectrogram(audioIn,fs);
    filename = sprintf('Cough%d.png',fileidx);
    imagename = fullfile(savefolder,sprintf('Cough_%d.png',fileidx));
    imwrite(S,imagename); %save image as png
end