Extract Signal Features

Per-frame feature extraction for 1D signals using the three Signal Processing Toolbox extractor objects. Picks the right extractor, configures it with real parameters only, and adds a GPU code path when one is available.

When to Use

• The user has a 1D signal and wants per-frame features for analysis or ML.
• The user names specific features from any of the three extractor domains (time, frequency, time-frequency).
• The user asks for a feature table or feature matrix to feed fitcecoc, fitcnet, or any classifier / regressor.
• The user asks for per-frame statistics over a windowed signal.

When NOT to Use

• Filter design or signal preprocessing — out of scope. Filtering before feature extraction is a separate concern.
• Audio-specific features (MFCC, mel-spectrogram, pitch, chroma, gammatone). Audio Toolbox's audioFeatureExtractor covers those — out of scope here.
• Batch / dataset orchestration — signalDatastore, labeledSignalSet, tall arrays. The per-file extraction is in scope; building the pipeline around it is not.
• 2D, image, or multivariate features — out of scope by signal-type boundary.

Workflow

0. (Recommended) Run a quick preliminary analysis. Check spectral stationarity — does the frequency content drift over time? — on a representative subset using Signal Processing Toolbox alone: a pspectrum(x, fs, "spectrogram") look plus a per-frame MeanFrequency drift ratio (no Econometrics Toolbox needed; adftest/kpsstest are an optional supplement only). Use the verdict to pick the primary extractor — non-stationary signals favour signalTimeFrequencyFeatureExtractor; spectrally stationary signals lean on the frequency extractor. See references/preliminary-analysis.md. Then write down a ranked candidate feature list, spanning more than one domain for a classifier/regressor feature table, with one-line justifications tying each feature to an observed signal characteristic, before configuring the extractors. The verdict picks the primary extractor, not the only one — a set that collapses onto a single extractor is the most common cause of a weak downstream classifier. Example: "MeanFrequency — stationary harmonic, energy localized at known frequencies." See references/feature-ranking.md.
1. Pick the extractor based on what the user wants. See "Choosing the right extractor" below.
2. Configure with SampleRate, FrameSize, and either FrameRate or FrameOverlapLength (not both). Enable feature flags as name-value pairs.
3. (Optional) Set per-feature or per-transform parameters via setExtractorParameters for features/transforms that have them. Only signalFrequencyFeatureExtractor and signalTimeFrequencyFeatureExtractor support this method. The second argument can be a feature name OR a transform name. Before writing any setExtractorParameters call, open the matching reference file and copy the parameter name verbatim. Parameter names are not what you'd guess. The references are the source of truth.
4. (Optional) Move to GPU using the guard pattern in references/gpu-patterns.md.
5. Run extract(sFE, x) on the signal. Output shape depends on FeatureFormat (matrix or table). src may also be a signalDatastore / audioDatastore, in which case extract returns one result per file (a cell array) and accepts UseParallel=true to process files on a parallel pool — use it whenever extracting over many files. For the input contract, the per-extractor output shape, datastore/parallel extraction, and how to combine outputs across extractors, see references/extract-function.md.
6. Decide output shape. Do NOT aggregate per-frame results by default. The per-frame table is a valid final output. Aggregate (mean/std across frames) only if the user's downstream model requires one fixed-length vector per signal (e.g., fitcecoc, fitcsvm, tree ensembles). If the model consumes sequences (LSTM, 1-D CNN, transformer), keep the per-frame table as-is. If the user has variable-length signals and the downstream task is unclear, ask rather than assuming aggregation. See references/post-extraction-patterns.md.

Stop and check the matching per-extractor reference before:

• Enabling any feature on signalTimeFrequencyFeatureExtractor — each Transform supports a different subset.
• Calling setExtractorParameters — parameter names differ per feature and per transform.
• Using any feature flag, parameter, or Transform value not already shown in this file's patterns. If it isn't in the per-extractor reference, it doesn't exist on the object.

Choosing the right extractor

User wants	Use
Time-domain features (amplitude, energy, shape factors)	signalTimeFeatureExtractor
Frequency-domain features (spectral location, power, bandwidth, PSD)	signalFrequencyFeatureExtractor
Time-frequency features (spectral shape, instantaneous, ridges, wavelet, EMD-derived)	signalTimeFrequencyFeatureExtractor
Multiple of the above	Use multiple extractors; concatenate the resulting tables

For the time-frequency extractor, the Transform property gates which features are valid. See the compatibility matrix in references/signal-time-frequency-feature-extractor.md.

Key Functions

Function	Purpose	Toolbox	Available From
signalTimeFeatureExtractor	Time-domain feature extractor object	Signal Processing Toolbox	R2021a
signalFrequencyFeatureExtractor	Frequency-domain feature extractor object	Signal Processing Toolbox	R2021b
signalTimeFrequencyFeatureExtractor	Time-frequency feature extractor object	Signal Processing Toolbox	R2024a
extract	Run a configured extractor on a signal	Signal Processing Toolbox	R2021a
getExtractorParameters / setExtractorParameters	Read/write per-feature or per-transform parameters (frequency and time-frequency only)	Signal Processing Toolbox	R2021b
timeFrequencyFeatureTransformOptions	Create transform options object for signalTimeFrequencyFeatureExtractor (replaces string Transform=)	Signal Processing Toolbox	R2026a
generateMATLABFunction	Emit a codegen-compatible MATLAB function from an extractor	Signal Processing Toolbox	R2021a
canUseGPU, gather	GPU availability check and data transfer (core MATLAB, no toolbox)	MATLAB	R2020b
gpuArray	Move array to GPU memory	Parallel Computing Toolbox	R2012a

gpuArray input to extract is available per extractor from: signalTimeFeatureExtractor R2023a, signalFrequencyFeatureExtractor R2023a, signalTimeFrequencyFeatureExtractor R2024b (one release after the object itself). Requires Parallel Computing Toolbox. See references/gpu-patterns.md for per-transform limitations.

generateMATLABFunction exists for codegen workflows. Mention it when relevant; full codegen guidance is out of scope for this skill.

Patterns

Time-domain features per frame

function featureTable = extractTimeFeaturesExample(x, fs)
%extractTimeFeaturesExample Per-frame time-domain features as a table.
    arguments
        x  (:, 1) double {mustBeFinite}
        fs (1, 1) double {mustBePositive}
    end

    sFE = signalTimeFeatureExtractor( ...
        SampleRate=fs, ...
        FrameSize=round(0.1 * fs), ...
        FrameOverlapLength=round(0.05 * fs), ...
        RMS=true, ...
        CrestFactor=true, ...
        PeakValue=true, ...
        FeatureFormat="table");

    featureTable = extract(sFE, x);
end

For valid time-feature flags, see references/signal-time-feature-extractor.md.

Frequency-domain features with per-feature parameters

function featureTable = extractBandPowerExample(x, fs)
%extractBandPowerExample Band power and occupied bandwidth per frame.
    arguments
        x  (:, 1) double {mustBeFinite}
        fs (1, 1) double {mustBePositive}
    end

    sFE = signalFrequencyFeatureExtractor( ...
        SampleRate=fs, ...
        FrameSize=round(0.1 * fs), ...
        FrameOverlapLength=round(0.05 * fs), ...
        BandPower=true, ...
        OccupiedBandwidth=true, ...
        FeatureFormat="table");

    setExtractorParameters(sFE, "OccupiedBandwidth", Percentage=95);

    featureTable = extract(sFE, x);
end

For per-feature parameter tables (including the trap that PowerBandwidth takes RelativeAmplitude not Power), see references/signal-frequency-feature-extractor.md.

Time-frequency features (spectrogram transform)

function featureTable = extractTFFeaturesExample(x, fs)
%extractTFFeaturesExample Spectral entropy and instantaneous frequency per frame.
    arguments
        x  (:, 1) double {mustBeFinite}
        fs (1, 1) double {mustBePositive}
    end

    % R2026a+ (preferred): use timeFrequencyFeatureTransformOptions.
    % Constructor is name-value only, keyed by FEATURE name -> transform.
    % There is no positional-string form: timeFrequencyFeatureTransformOptions("spectrogram") errors.
    tfOpts = timeFrequencyFeatureTransformOptions( ...
        SpectralEntropy="spectrogram", ...
        InstantaneousFrequency="spectrogram");
    sFE = signalTimeFrequencyFeatureExtractor( ...
        Transform=tfOpts, ...
        SampleRate=fs, ...
        FrameSize=256, ...
        FrameOverlapLength=128, ...
        SpectralEntropy=true, ...
        InstantaneousFrequency=true, ...
        FeatureFormat="table");

    % R2024a–R2025b: use string directly (deprecated from R2026a)
    % sFE = signalTimeFrequencyFeatureExtractor( ...
    %     Transform="spectrogram", ...
    %     SampleRate=fs, ...
    %     FrameSize=256, ...
    %     FrameOverlapLength=128, ...
    %     SpectralEntropy=true, ...
    %     InstantaneousFrequency=true, ...
    %     FeatureFormat="table");

    setExtractorParameters(sFE, "spectrogram", Leakage=0.9, OverlapPercent=85);

    featureTable = extract(sFE, x);
end

Each Transform supports a different subset of features, and per-feature parameters depend on (transform, feature). Always check references/signal-time-frequency-feature-extractor.md before enabling a feature or calling setExtractorParameters.

Multi-transform routing (R2026a+): A single extractor can route different features to different transforms — you do NOT need separate extractors. Use timeFrequencyFeatureTransformOptions with per-feature properties (e.g., SpectralKurtosis="synchrosqueezedspectrogram", SpectralEntropy="spectrogram"). See the full example and valid-transform table in references/signal-time-frequency-feature-extractor.md.

GPU-accelerated extraction

Toolbox note: The GPU path (gpuArray) and the UseParallel=true datastore path both require Parallel Computing Toolbox. It is not required for core feature extraction — the skill runs fully on CPU without it, because the canUseGPU() guard skips the GPU branch and UseParallel defaults to false. Enable these paths only when Parallel Computing Toolbox is installed.

function featureTable = extractWithGPU(x, fs)
%extractWithGPU Run feature extraction on GPU when available, CPU otherwise.
    arguments
        x  (:, 1) double {mustBeFinite}
        fs (1, 1) double {mustBePositive}
    end

    sFE = signalTimeFeatureExtractor( ...
        SampleRate=fs, ...
        FrameSize=round(0.1 * fs), ...
        FrameOverlapLength=round(0.05 * fs), ...
        RMS=true, ...
        StandardDeviation=true, ...
        FeatureFormat="table");

    if canUseGPU()
        x = gpuArray(x);
    end
    featureTable = extract(sFE, x);
end

The feature table may contain gpuArray columns. Downstream code (ML training, plotting) often accepts these directly. Call gather only when a specific consumer requires it (e.g., save to .mat, writetable to CSV).

See references/gpu-patterns.md for the rationale behind the canUseGPU guard and why unconditional gpuArray calls are wrong. If the GPU path unexpectedly falls back to CPU or gpuArray errors, the matlab-setup-gpu skill diagnoses GPU availability problems (unlicensed PCT, outdated driver, compute mode).

Post-extraction: aggregation and reproducibility

Do not aggregate unless the user's workflow explicitly requires one feature vector per signal. The per-frame table is the default output. Two optional patterns that run after extract:

• Per-frame → per-signal aggregation — only when the downstream model requires a fixed-length vector per example (tree ensembles, SVM, etc.). Collapse with varfun(@mean, ...) / varfun(@std, ...), dropping FrameStartTime / FrameEndTime first. Skip aggregation for sequence models (LSTM, 1-D CNN) that consume the frame sequence directly. For scalar summaries of vector-valued features, use setScalarizationMethods at extraction time instead.
• Save extractor + data card — save("featureConfig.mat", "sFE", "dataCard") where dataCard records SampleRate, FrameSize, FrameOverlapLength, class(sFE), and version("-release"). Minimum sidecar to reproduce the extraction on new data.

See references/post-extraction-patterns.md for the worked code blocks and edge cases (vector-valued columns, label-column handling, alternative scalarization route).

Conventions (apply to all three extractors)

• Always set SampleRate. Frequency-derived features interpret the signal as fs = 1 if SampleRate is omitted.
• Pick FrameRate or FrameOverlapLength, not both. They control the same thing two different ways. Setting both raises an error.
• FrameOverlapLength must be < FrameSize.
• Set FrameSize and FrameOverlapLength in samples, not seconds. Convert: FrameSize = round(durationSeconds * fs).
• Prefer FeatureFormat="table" when the extractor produces a mix of scalar and vector features.
• FrameStartTime / FrameEndTime are 1-indexed sample positions, not seconds. Convert: tSec = (T.FrameStartTime - 1) / fs. Strip them before training a classifier.
• Vector-valued feature columns are numeric matrices when per-frame length is fixed, cells when it varies. Check with iscell(T.(colName)) before indexing.
• Don't guess feature names or parameters. Read the relevant per-extractor reference. Anything not in the reference does not exist on the object.

Common cross-cutting pitfalls

What you tried	Fix
Hand-rolled per-frame statistics over a windowed signal (e.g. RMS / crest factor loop on a buffered signal)	Use the extractor object — composes with extract, has a codegen path.
FrameLength=N instead of FrameSize=N	Property is FrameSize on all three extractors.
Set both FrameRate and FrameOverlapLength	Pick one.
gpuArray(x) without canUseGPU() guard	Hard-errors on CPU-only machines. Wrap in if canUseGPU(); x = gpuArray(x); end.

For extractor-specific pitfalls (e.g., Skewness=true on the time extractor, MeanEnvelopeEnergy on a non-EMD transform, the PowerBandwidth parameter being RelativeAmplitude rather than guessed from the feature name), see the per-extractor references.

References

• references/preliminary-analysis.md — Signal-Processing-only spectral-stationarity check (pspectrum spectrogram + per-frame MeanFrequency drift ratio), the optional Econometrics adftest/kpsstest supplement, and the verdict→extractor decision rules. Read before picking an extractor when the signal character is unclear.
• references/feature-ranking.md — a-priori candidate-feature list pattern and the signal-profile→feature mapping. Read when the user asks for a starting feature set or wants a ranked list.
• references/extract-function.md — extract input/output contract, per-extractor output character, multi-extractor row alignment, and common error modes. Read when debugging shape or alignment issues.
• references/signal-time-feature-extractor.md — full property and feature-flag surface for the time extractor. Read when verifying a time-feature name or property.
• references/signal-frequency-feature-extractor.md — full property surface plus per-feature parameter tables (OccupiedBandwidth, PowerBandwidth, WelchPSD, peak parameters). Read when configuring frequency features.
• references/signal-time-frequency-feature-extractor.md — Transform×feature compatibility matrix and per-transform parameter tables. Read this before enabling any feature on the time-frequency extractor.
• references/scalarization-options.md — the three *ScalarFeatureOptions objects and the setScalarizationMethods API. Read when adding scalar summary columns to vector-valued features.
• references/gpu-patterns.md — canUseGPU guard pattern and rationale. Read when the user mentions GPU.

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