Download and unzip the Audio Toolbox™ model for VGGish.

Type vggish at the Command Window. If the Audio Toolbox model for VGGish is not installed, then the function provides a link to the location of the network weights. To download the model, click the link. Unzip the file to a location on the MATLAB path.

Alternatively, execute these commands to download and unzip the VGGish model to your temporary directory.

downloadFolder = fullfile(tempdir,'VGGishDownload');
loc = websave(downloadFolder,'https://ssd.bat365/supportfiles/audio/vggish.zip');
VGGishLocation = tempdir;
unzip(loc,VGGishLocation)
addpath(fullfile(VGGishLocation,'vggish'))

Check that the installation is successful by typing vggish at the Command Window. If the network is installed, then the function returns a SeriesNetwork (Deep Learning Toolbox) object.

vggish

ans = 
  SeriesNetwork with properties:

         Layers: [24×1 nnet.cnn.layer.Layer]
     InputNames: {'InputBatch'}
    OutputNames: {'regressionoutput'}

Load a pretrained VGGish convolutional neural network and examine the layers and classes.

Use vggish to load the pretrained VGGish network. The output net is a SeriesNetwork (Deep Learning Toolbox) object.

net = vggish

net = 
  SeriesNetwork with properties:

         Layers: [24×1 nnet.cnn.layer.Layer]
     InputNames: {'InputBatch'}
    OutputNames: {'regressionoutput'}

View the network architecture using the Layers property. The network has 24 layers. There are nine layers with learnable weights, of which six are convolutional layers and three are fully connected layers.

net.Layers

ans = 
  24×1 Layer array with layers:

     1   'InputBatch'         Image Input         96×64×1 images
     2   'conv1'              Convolution         64 3×3×1 convolutions with stride [1  1] and padding 'same'
     3   'relu'               ReLU                ReLU
     4   'pool1'              Max Pooling         2×2 max pooling with stride [2  2] and padding 'same'
     5   'conv2'              Convolution         128 3×3×64 convolutions with stride [1  1] and padding 'same'
     6   'relu2'              ReLU                ReLU
     7   'pool2'              Max Pooling         2×2 max pooling with stride [2  2] and padding 'same'
     8   'conv3_1'            Convolution         256 3×3×128 convolutions with stride [1  1] and padding 'same'
     9   'relu3_1'            ReLU                ReLU
    10   'conv3_2'            Convolution         256 3×3×256 convolutions with stride [1  1] and padding 'same'
    11   'relu3_2'            ReLU                ReLU
    12   'pool3'              Max Pooling         2×2 max pooling with stride [2  2] and padding 'same'
    13   'conv4_1'            Convolution         512 3×3×256 convolutions with stride [1  1] and padding 'same'
    14   'relu4_1'            ReLU                ReLU
    15   'conv4_2'            Convolution         512 3×3×512 convolutions with stride [1  1] and padding 'same'
    16   'relu4_2'            ReLU                ReLU
    17   'pool4'              Max Pooling         2×2 max pooling with stride [2  2] and padding 'same'
    18   'fc1_1'              Fully Connected     4096 fully connected layer
    19   'relu5_1'            ReLU                ReLU
    20   'fc1_2'              Fully Connected     4096 fully connected layer
    21   'relu5_2'            ReLU                ReLU
    22   'fc2'                Fully Connected     128 fully connected layer
    23   'EmbeddingBatch'     ReLU                ReLU
    24   'regressionoutput'   Regression Output   mean-squared-error

Use analyzeNetwork (Deep Learning Toolbox) to visually explore the network.

analyzeNetwork(net)

Read in an audio signal to extract feature embeddings from it.

[audioIn,fs] = audioread("Ambiance-16-44p1-mono-12secs.wav");

Plot and listen to the audio signal.

t = (0:numel(audioIn)-1)/fs;
plot(t,audioIn)
xlabel("Time (s)")
ylabel("Ampltiude")
axis tight

% To play the sound, call soundsc(audioIn,fs)

VGGish requires you to preprocess the audio signal to match the input format used to train the network. The preprocesssing steps include resampling the audio signal and computing an array of mel spectrograms. To learn more about mel spectrograms, see melSpectrogram. Use vggishPreprocess to preprocess the signal and extract the mel spectrograms to be passed to VGGish. Visualize one of these spectrograms chosen at random.

spectrograms = vggishPreprocess(audioIn,fs);

arbitrarySpect = spectrograms(:,:,1,randi(size(spectrograms,4)));
surf(arbitrarySpect,EdgeColor="none")
view(90,-90)
xlabel("Mel Band")
ylabel("Frame")
title("Mel Spectrogram for VGGish")
axis tight

Create a VGGish neural network. Using the vggish function requires installing the pretrained VGGish network. If the network is not installed, the function provides a link to download the pretrained model.

net = vggish;

Call predict with the network on the preprocessed mel spectrogram images to extract feature embeddings. The feature embeddings are returned as a numFrames-by-128 matrix, where numFrames is the number of individual spectrograms and 128 is the number of elements in each feature vector.

features = predict(net,spectrograms);
[numFrames,numFeatures] = size(features)

numFrames = 24

numFeatures = 128

Visualize the VGGish feature embeddings.

surf(features,EdgeColor="none")
view([90 -90])
xlabel("Feature")
ylabel("Frame")
title("VGGish Feature Embeddings")
axis tight

In this example, you transfer the learning in the VGGish regression model to an audio classification task.

Download and unzip the environmental sound classification data set. This data set consists of recordings labeled as one of 10 different audio sound classes (ESC-10).

downloadFolder = matlab.internal.examples.downloadSupportFile("audio","ESC-10.zip");
unzip(downloadFolder,tempdir)
dataLocation = fullfile(tempdir,"ESC-10");

Create an audioDatastore object to manage the data and split it into train and validation sets. Call countEachLabel to display the distribution of sound classes and the number of unique labels.

ads = audioDatastore(dataLocation,IncludeSubfolders=true,LabelSource="foldernames");
labelTable = countEachLabel(ads)

labelTable=10×2 table
        Label         Count
    ______________    _____

    chainsaw           40  
    clock_tick         40  
    crackling_fire     40  
    crying_baby        40  
    dog                40  
    helicopter         40  
    rain               40  
    rooster            38  
    sea_waves          40  
    sneezing           40  

Determine the total number of classes.

numClasses = height(labelTable);

Call splitEachLabel to split the data set into train and validation sets. Inspect the distribution of labels in the training and validation sets.

[adsTrain, adsValidation] = splitEachLabel(ads,0.8);

countEachLabel(adsTrain)

ans=10×2 table
        Label         Count
    ______________    _____

    chainsaw           32  
    clock_tick         32  
    crackling_fire     32  
    crying_baby        32  
    dog                32  
    helicopter         32  
    rain               32  
    rooster            30  
    sea_waves          32  
    sneezing           32  

countEachLabel(adsValidation)

ans=10×2 table
        Label         Count
    ______________    _____

    chainsaw            8  
    clock_tick          8  
    crackling_fire      8  
    crying_baby         8  
    dog                 8  
    helicopter          8  
    rain                8  
    rooster             8  
    sea_waves           8  
    sneezing            8  

The VGGish network expects audio to be preprocessed into log mel spectrograms. Use vggishPreprocess to extract the spectrograms from the train set. There are multiple spectrograms for each audio signal. Replicate the labels so that they are in one-to-one correspondence with the spectrograms.

overlapPercentage = 75;

trainFeatures = [];
trainLabels = [];
while hasdata(adsTrain)
    [audioIn,fileInfo] = read(adsTrain);
    features = vggishPreprocess(audioIn,fileInfo.SampleRate,OverlapPercentage=overlapPercentage);
    numSpectrograms = size(features,4);
    trainFeatures = cat(4,trainFeatures,features);
    trainLabels = cat(2,trainLabels,repelem(fileInfo.Label,numSpectrograms));
end

Extract spectrograms from the validation set and replicate the labels.

validationFeatures = [];
validationLabels = [];
segmentsPerFile = zeros(numel(adsValidation.Files), 1);
idx = 1;
while hasdata(adsValidation)
    [audioIn,fileInfo] = read(adsValidation);
    features = vggishPreprocess(audioIn,fileInfo.SampleRate,OverlapPercentage=overlapPercentage);
    numSpectrograms = size(features,4);
    validationFeatures = cat(4,validationFeatures,features);
    validationLabels = cat(2,validationLabels,repelem(fileInfo.Label,numSpectrograms));

    segmentsPerFile(idx) = numSpectrograms;
    idx = idx + 1;
end

Load the VGGish model and convert it to a layerGraph (Deep Learning Toolbox) object.

net = vggish;

lgraph = layerGraph(net.Layers);

Use removeLayers (Deep Learning Toolbox) to remove the final regression output layer from the graph. After you remove the regression layer, the new final layer of the graph is a ReLU layer named 'EmbeddingBatch'.

lgraph = removeLayers(lgraph,"regressionoutput");
lgraph.Layers(end)

ans = 
  ReLULayer with properties:

    Name: 'EmbeddingBatch'

Use addLayers (Deep Learning Toolbox) to add a fullyConnectedLayer (Deep Learning Toolbox), a softmaxLayer (Deep Learning Toolbox), and a classificationLayer (Deep Learning Toolbox) to the graph. Set the WeightLearnRateFactor and BiasLearnRateFactor of the new fully connected layer to 10 so that learning is faster in the new layer than in the transferred layers.

lgraph = addLayers(lgraph,[ ...
    fullyConnectedLayer(numClasses,Name="FCFinal",WeightLearnRateFactor=10,BiasLearnRateFactor=10)
    softmaxLayer(Name="softmax")
    classificationLayer(Name="classOut")]);

Use connectLayers (Deep Learning Toolbox) to append the fully connected, softmax, and classification layers to the layer graph.

lgraph = connectLayers(lgraph,"EmbeddingBatch","FCFinal");

To define training options, use trainingOptions (Deep Learning Toolbox).

miniBatchSize = 128;
options = trainingOptions("adam", ...
    MaxEpochs=5, ...
    MiniBatchSize=miniBatchSize, ...
    Shuffle="every-epoch", ...
    ValidationData={validationFeatures,validationLabels}, ...
    ValidationFrequency=50, ...
    LearnRateSchedule="piecewise", ...
    LearnRateDropFactor=0.5, ...
    LearnRateDropPeriod=2, ...
    OutputNetwork="best-validation-loss", ...
    Verbose=false, ...
    Plots="training-progress");

To train the network, use trainNetwork (Deep Learning Toolbox).

[trainedNet, netInfo] = trainNetwork(trainFeatures,trainLabels,lgraph,options);

Each audio file was split into several segments to feed into the VGGish network. Combine the predictions for each file in the validation set using a majority-rule decision.

validationPredictions = classify(trainedNet,validationFeatures);

idx = 1;
validationPredictionsPerFile = categorical;
for ii = 1:numel(adsValidation.Files)
    validationPredictionsPerFile(ii,1) = mode(validationPredictions(idx:idx+segmentsPerFile(ii)-1));
    idx = idx + segmentsPerFile(ii);
end

Use confusionchart (Deep Learning Toolbox) to evaluate the performance of the network on the validation set.

figure(Units="normalized",Position=[0.2 0.2 0.5 0.5]);
confusionchart(adsValidation.Labels,validationPredictionsPerFile, ...
    Title=sprintf("Confusion Matrix for Validation Data \nAccuracy = %0.2f %%",mean(validationPredictionsPerFile==adsValidation.Labels)*100), ...
    ColumnSummary="column-normalized", ...
    RowSummary="row-normalized")