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Preprocess audio for voice activity detection (VAD) network

Since R2023a



    features = vadnetPreprocess(audioIn,fs) returns a mel spectrogram from the audio input that you can feed to the pretrained VAD network returned by audioPretrainedNetwork.


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    Read in an audio signal containing speech and music and listen to the sound.

    [audioIn,fs] = audioread("MusicAndSpeech-16-mono-14secs.ogg");

    Use vadnetPreprocess to preprocess the audio by computing a mel spectrogram.

    features = vadnetPreprocess(audioIn,fs);

    Call audioPretrainedNetwork to obtain a pretrained VAD neural network.

    net = audioPretrainedNetwork("vadnet");

    Pass the preprocessed audio through the network to obtain the probability of speech in each frame.

    probs = predict(net,features);

    Use vadnetPosprocess to postprocess the network output and determine the boundaries of the speech regions in the signal.

    roi = vadnetPostprocess(audioIn,fs,probs)
    roi = 2×2
               1       63120
           83600      150000

    Plot the audio with the detected speech regions.


    Create a dsp.AudioFileReader object to stream an audio file for processing. Set the SamplesPerFrame property to read 100 ms nonoverlapping chunks from the signal.

    afr = dsp.AudioFileReader("MaleVolumeUp-16-mono-6secs.ogg");
    analysisDuration = 0.1; % seconds
    afr.SamplesPerFrame = floor(analysisDuration*afr.SampleRate);

    The vadnet architecture does not retain state between calls, and it performs best when analyzing larger chunks of audio signals. When you use vadnet in a streaming scenario, specific application requirements of accuracy, computational efficiency, and latency dictate the analysis duration and whether to overlap analysis chunks.

    Create a timescope object to plot the audio signal and the corresponding speech probabilities. Create an audioDeviceWriter to play the audio as you stream it.

    scope = timescope(NumInputPorts=2, ...
        SampleRate=afr.SampleRate, ...
        TimeSpanSource="property",TimeSpan=5, ...
        YLimits=[-1.2,1.2], ...
        ShowLegend=true,ChannelNames=["Audio","Speech Probability"]);
    adw = audioDeviceWriter(afr.SampleRate);

    Call audioPretrainedNetwork to obtain a pretrained VAD neural network.

    net = audioPretrainedNetwork("vadnet");

    In a streaming loop:

    1. Read in a 100 ms chunk from the audio file.

    2. Preprocess the audio into a mel spectrogram using vadnetPreprocess.

    3. Use the VAD network to predict the probability of speech in each frame of the spectrogram. Replicate the probabilities to correspond to each sample in the audio signal.

    4. Plot the audio signal and the probabilities of speech.

    5. Play the audio with the device writer.

    hop = 0.01 * afr.SampleRate;
    while ~isDone(afr)
        audioIn = afr();
        features = vadnetPreprocess(audioIn,afr.SampleRate);
        probs = predict(net,features);
        % Replicate probs to correspond to samples in audioIn
        probs = repelem(probs,hop)';
        probs = probs((hop/2)+1:end-hop/2);

    Input Arguments

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    Audio input signal, specified as a column vector (single channel).

    Data Types: single | double

    Sample rate in Hz, specified as a positive scalar.

    Data Types: single | double

    Output Arguments

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    Mel spectrogram, returned as a 40-by-T matrix, where T is the number of spectra in the spectrogram.


    The vadnetPreprocess function preprocesses the audio data using the following steps.

    1. Resample the audio to 16kHz.

    2. Compute a centered short-time Fourier transform (STFT) using a 25 ms periodic Hamming window and 10 ms hop length. Pad the signal so that the first window is centered at 0 s.

    3. Convert the STFT to a power spectrogram.

    4. Apply a mel filter bank with 40 bands to obtain a mel spectrogram.

    5. Convert the mel spectrogram to a log scale.

    6. Standardize each of the mel bands to have zero mean and standard deviation of 1.

    Extended Capabilities

    C/C++ Code Generation
    Generate C and C++ code using MATLAB® Coder™.

    Version History

    Introduced in R2023a