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Label Spoken Words in Audio Signals

This example shows how to label spoken words in Signal Labeler. The example uses the IBM® Watson Speech to Text API and Audio Toolbox™ software. Speech-to-Text Transcription (Audio Toolbox) provides instructions for:

  1. Downloading the Audio Toolbox speech2text extended functionality, available from MATLAB® Central.

  2. Setting up the IBM Watson Speech API, offered through IBM Cloud Services. You must create an IBM Cloud account, a Speech to Text service instance, and go to the service dashboard and copy your credentials – API Key and URL values. For more details, see the Getting Started Tutorial in the IBM documentation.

Set Up Speech Client

To perform speech-to-text transcription, you must create a speechClient object. Make sure the speech2text P-code files and the JSON file that stores your IBM Cloud credentials are in the current folder or on the MATLAB path.

speechObjectIBM = speechClient("IBM",timestamps=true);

Load an audio data file containing the sentence "Oak is strong, and also gives shade" spoken by a male voice. The signal is sampled at 44.1 kHz.

[y,fs] = audioread("oak.m4a");

% To hear, type soundsc(y,fs)

Define Label

Open Signal Labeler and define a label to attach to the signal. Click Add on the Labeler tab, then Add Label Definition. Specify the Label Name as Words, select a Label Type of ROI, and select a Data Type of string.

Import Speech Data

Import the signal into the app.

  1. On the Labeler tab, click Import and select From Workspace in the Members list. In the dialog box, select the signal y.

  2. Add time information. Select Time from the drop-down list and specify fs as the sample rate, which is measured in Hz.

  3. Click Import and Close. The signal appears in the Labeled Signal Set Browser.

Locate and Identify Spoken Words

Locate and identify the words spoken in the input signal.

  1. Select Words in the Label Definitions browser.

  2. On the Automated Value gallery, select Speech to Text.

  3. Click Auto-Label and select Auto-Label All Signals.

  4. In the dialog box, select IBM from the Service Name list and select the check box next to Segment Words.

  5. Click OK.

Signal Labeler locates and labels the spoken words. In the Labeled Signal Set Browser, select the check box next to y to plot the signal. Expand Words and select the check box next to each word to visualize the corresponding labeled region.

Export Labeled Signal

Export the labeled signal. On the Labeler tab, click Export and select To File from the Labeled Signal Set list. In the dialog box that appears, give the name Transcription.mat to the labeled signal set and add an optional short description. Click Export.

Go back to the MATLAB Command Window. Load the labeled signal set. The set has only one member. Get the names of the labels, and use the name to obtain and display the transcribed words.

load Transcription

ln = getLabelNames(transcribedAudio);

v = getLabelValues(transcribedAudio,1,ln)
v=7×2 table
     ROILimits       Value  
    ____________    ________

    0.09    0.56    "oak"   
    0.59    0.97    "is"    
       1    1.78    "strong"
    1.94    2.19    "and"   
    2.22    2.67    "also"  
    2.67    3.22    "gives" 
    3.25    3.91    "shade" 

Change the label values from strings to categories. Use a signalMask object to plot the signal using a different color for each word.

v.Value = categorical(v.Value,v.Value);

msk = signalMask(v,SampleRate=fs);

s = getSignal(transcribedAudio,1);


Create a logical vector of the same length as the audio signal. Set to true the signal segment where the speaker utters the word "is."

bsl = binmask(msk,height(s));

plot(s.Time,[s.y bsl(:,v.Value=="is")])

See Also



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