Custom Labeling Functions

You can use Signal Labeler to perform automated labeling tasks. Apart from Peak Labeler, the Automate Value gallery on the Label tab contains functions that you can use to label signals automatically.

Automate Value gallery

Create Custom Labeling Functions

The first line in every custom autolabeling function consists of a definition statement of the form

function [labelVals,labelLocs] = fx(x,t,parentLabelVal,parentLabelLoc,varargin)

The definition statement contains the function name and a set of mandatory and optional arguments:

The first input argument, x, is the input signal. When writing the function, expect x to be a matrix where each column contains data corresponding to a channel. If the channels have different lengths, then expect x to be a cell array of column vectors.
The second input argument, t, stores the time values. When writing the function, expect t to be a matrix where each column contains time information corresponding to a channel. If the channels have different lengths, then expect t to be a cell array of column vectors.
Note
- For single-channel members, custom autolabeling functions get data and time values as double-precision vectors.
- For multichannel members, custom autolabeling functions get data and time values as matrices or cell arrays.
- Custom autolabeling functions get all the channels of a member as input, but they do not have to operate on all. You can choose which channels you want the function to operate on.
The third input argument, parentLabelVal, is the parent label value associated with the output sublabel and contains a numeric, logical, or string scalar. This argument is passed in only for functions that automate the labeling of sublabels. If the function is for a parent label, expect parentLabelVal to be empty.
The fourth input argument, parentLabelLoc, contains:
- An empty vector when the parent label is an attribute
- A two-element numeric row vector of region of interest (ROI) limits when the parent label is an ROI
- A numeric scalar representing a point location when the parent label is a point
This argument is passed in only for functions that automate the labeling of sublabels. If the function is for a parent label, expect parentLabelLoc to be empty.
Note
- For parent labels, the autolabeling function operates on each selected member.
- For sublabels, the autolabeling function operates on one parent label instance at a time for each selected member.
Use varargin to specify additional input arguments. If you do not have additional input arguments, you can omit varargin. Enter the additional arguments as an ordered comma-separated list in the dialog box that appears when you click the Auto-Label button.
The first output argument, labelVals, contains the label values. labelVals must be:
- A numeric, logical, or string scalar when the output labels are attributes
- A column vector with numeric, logical, or string values when the output labels are ROIs or points
The second output argument, labelLocs, contains the label locations. labelLocs must be:
- An empty vector when the output labels are attributes
- A two-column matrix of ROI limits when the output labels are ROIs
- A column vector of point locations when the output labels are points
To implement your algorithm, you can use any function from MATLAB^® or from any toolbox installed in your system.

For more details, see Automate Signal Labeling with Custom Functions and Label Spoken Words in Audio Signals.

Example: Mean RMS Value

This function computes the mean RMS value of a signal and labels the signal with the value as a numeric attribute. If a member has more than one channel, the function computes the RMS value of each channel and averages the values. The channels can have different lengths.

function [labelVals,labelLocs] = meanRMS(x,t,parentLabelVal,parentLabelLoc,varargin)
% Label signal with its mean RMS value as attribute

if iscell(x)
    labelVals = mean(cellfun(@rms,x))
else
    labelVals = mean(rms(x));
end
labelLocs = [];

end

Example: Zero Crossings

This function finds the zero crossings of a signal and labels them as "rising" for positive-going transitions and "falling" for negative-going transitions.

function [labelVals,labelLocs] = transitions(x,t,parentLabelVal,parentLabelLoc,varargin)
% Label zero crossings as "rising" or "falling"

nchan = size(x,2);
tt = t(:,1);

labelVals = cell(nchan,1);
labelLocs = cell(nchan,1);

for kj = 1:nchan

    [rate,count,indices] = zerocrossrate(x,TransitionEdge="rising");
    rloc = tt(indices == 1);
    rval = repmat("rising",length(rloc),1);
    
    [rate,count,indices] = zerocrossrate(x,TransitionEdge="falling");
    floc = tt(indices == 1);
    fval = repmat("falling",length(floc),1);
    
    labelLocs{kj} = [rloc;floc];
    labelVals{kj} = [rval;fval];

end

labelVals = cat(1,labelVals{:});
labelLocs = cell2mat(labelLocs);

end

Example: Multichannel Labeling

This logical function labels as true those regions of a multichannel signal where:

The amplitude of the first channel is negative.
The amplitude of the third channel is larger than a user-specified value, mx. If not specified, mx defaults to 0.1.

function [labelVals,labelLocs] = greaterThan(x,t,parentLabelVal,parentLabelLoc,varargin)
% Label regions with negative first channel and third channel larger than a given value

if nargin<5
    mx = 0.1;
else
    mx = varargin{1};
end

xr = x(:,1);
xx = x(:,3);
tt = t(:,1);

ss = signalMask(xr < 0 & xx >= mx);
x = roimask(ss);

labelLocs = tt(x.ROILimits);
labelVals = logical(double(x.Value));

end

Example: Extract Spoken Words Using External API

This function uses the IBM® Watson Speech to Text API and the Audio Toolbox™ speech2text extended functionality to extract spoken words from an audio file.

function [labelVals,labelLocs] = stt(x,t,parentLabelVal,parentLabelLoc,varargin)

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

fs = 1/(t(2)-t(1));

tixt = speech2text(aspeechObjectIBM,x,fs);

unifiedTable = vertcat(tixt.TimeStamps{:});
numLabels = numel(unifiedTable,1);
labelVals = strings(numLabels,1);
labelLocs = zeros(numLabels,2);

for idx = 1:numLabels
    labelVals(idx) = unifiedTable{idx}{1};
    labelLocs(idx,1) = unifiedTable{idx}{2};
    labelLocs(idx,2) = unifiedTable{idx}{3};
end

end

Add Custom Labeling Functions to the Gallery

To add a custom autolabeling function, click the arrow next to the Automate Value gallery and then select Add Custom Function. In the dialog box, specify these fields:

Name — Specify the name of the function you want to add.
Description — Add a short description of what the function does and describe the optional input arguments.
Label Type — Specify the type of label that the function generates. Select Attribute (the default), ROI, or Point.
Note
Based on the Label Type you specify, Signal Labeler places the function in the appropriate category in the Automate Value gallery. When you select a label definition, the gallery enables only those functions that can be used with that definition type.

If you have already written a function, and the function is in the current folder or in the MATLAB path, Signal Labeler incorporates it in the gallery. If you have not written the function yet, Signal Labeler opens a blank template in the Editor.

Manage Custom Labeling Functions in Gallery

At any time, you can edit functions, edit function descriptions, or remove functions using the Manage Custom Functions option in the Automate Value gallery.

Note

Using the Manage Custom Functions option changes only the function descriptions displayed in the Automate Value gallery. If you want to change the description in the file that contains the function, you must edit the file.