info

Output mapping and individual feature extractor parameters

Syntax

idx = info(aFE)

idx = info(aFE,"all")

[idx,params] = info(___)

Description

idx = info(aFE) returns a struct with field names corresponding to enabled feature extractors. The field values correspond to the column indices that the extracted features occupy in the output from extract.

idx = info(aFE,"all") returns a struct with field names corresponding to all available feature extractors. If the feature extractor is disabled, the field value is empty.

[idx,params] = info(___) returns a second struct, params. The field names of params correspond to the feature extractors with settable parameters. If the "all" flag is specified, params contains all feature extractors with settable parameters. If the "all" flag is not specified, params contains only the enabled feature extractors with settable parameters. You can set parameters using setExtractorParameters.

Examples

Interpret Output from extract

Extract the mel spectrum, mel spectral centroid, and mel spectral skewness from concatenated white and pink noise.

fs = 48e3;
aFE = audioFeatureExtractor("SampleRate",fs, ...
    "melSpectrum",true, ...
    "SpectralDescriptorInput","melSpectrum", ...
    "spectralCentroid",true, ...
    "spectralSkewness",true);

features = extract(aFE,[2*rand(fs,1)-1;pinknoise(fs,1)]);

Use info to determine which columns of the output correspond to which feature. Plot the features separately.

idx = info(aFE);

surf(log10(features(:,idx.melSpectrum)),"EdgeColor","none");
view([90,-90])
axis tight
title("Mel Spectrum")
ylabel("Analysis Frame Number")

plot(features(:,idx.spectralCentroid))
axis tight
title("Mel Spectral Centroid")
xlabel("Analysis Frame Number")

plot(features(:,idx.spectralSkewness))
axis tight
title("Mel Spectral Skewness")
xlabel("Analysis Frame Number")

Get List of All Features audioFeatureExtractor Provides

Create a default audioFeatureExtractor object. By default, all feature extractors are disabled.

aFE = audioFeatureExtractor

aFE = 
  audioFeatureExtractor with properties:

   Properties
                     Window: [1024x1 double]
              OverlapLength: 512
                 SampleRate: 44100
                  FFTLength: []
    SpectralDescriptorInput: 'linearSpectrum'
        FeatureVectorLength: 0

   Enabled Features
     none

   Disabled Features
     linearSpectrum, melSpectrum, barkSpectrum, erbSpectrum, mfcc, mfccDelta
     mfccDeltaDelta, gtcc, gtccDelta, gtccDeltaDelta, spectralCentroid, spectralCrest
     spectralDecrease, spectralEntropy, spectralFlatness, spectralFlux, spectralKurtosis, spectralRolloffPoint
     spectralSkewness, spectralSlope, spectralSpread, pitch, harmonicRatio, zerocrossrate
     shortTimeEnergy


   To extract a feature, set the corresponding property to true.
   For example, obj.mfcc = true, adds mfcc to the list of enabled features.

The info function returns information about enabled feature extractors. To view information about all feature extractors, call info using the "all" flag.

[idx,params] = info(aFE,"all")

idx = struct with fields:
          linearSpectrum: [1x0 double]
             melSpectrum: [1x0 double]
            barkSpectrum: [1x0 double]
             erbSpectrum: [1x0 double]
                    mfcc: [1x0 double]
               mfccDelta: [1x0 double]
          mfccDeltaDelta: [1x0 double]
                    gtcc: [1x0 double]
               gtccDelta: [1x0 double]
          gtccDeltaDelta: [1x0 double]
        spectralCentroid: [1x0 double]
           spectralCrest: [1x0 double]
        spectralDecrease: [1x0 double]
         spectralEntropy: [1x0 double]
        spectralFlatness: [1x0 double]
            spectralFlux: [1x0 double]
        spectralKurtosis: [1x0 double]
    spectralRolloffPoint: [1x0 double]
        spectralSkewness: [1x0 double]
           spectralSlope: [1x0 double]
          spectralSpread: [1x0 double]
                   pitch: [1x0 double]
           harmonicRatio: [1x0 double]
           zerocrossrate: [1x0 double]
         shortTimeEnergy: [1x0 double]

params = struct with fields:
          linearSpectrum: [1x1 struct]
             melSpectrum: [1x1 struct]
            barkSpectrum: [1x1 struct]
             erbSpectrum: [1x1 struct]
                    mfcc: [1x1 struct]
                    gtcc: [1x1 struct]
            spectralFlux: [1x1 struct]
    spectralRolloffPoint: [1x1 struct]
                   pitch: [1x1 struct]
           zerocrossrate: [1x1 struct]

Use the idx struct to enable all feature extractors on the audioFeatureExtractor object.

features = fieldnames(idx);
for i = 1:numel(features)
    aFE.(features{i}) = true;
end
aFE

aFE = 
  audioFeatureExtractor with properties:

   Properties
                     Window: [1024x1 double]
              OverlapLength: 512
                 SampleRate: 44100
                  FFTLength: []
    SpectralDescriptorInput: 'linearSpectrum'
        FeatureVectorLength: 713

   Enabled Features
     linearSpectrum, melSpectrum, barkSpectrum, erbSpectrum, mfcc, mfccDelta
     mfccDeltaDelta, gtcc, gtccDelta, gtccDeltaDelta, spectralCentroid, spectralCrest
     spectralDecrease, spectralEntropy, spectralFlatness, spectralFlux, spectralKurtosis, spectralRolloffPoint
     spectralSkewness, spectralSlope, spectralSpread, pitch, harmonicRatio, zerocrossrate
     shortTimeEnergy

   Disabled Features
     none


   To extract a feature, set the corresponding property to true.
   For example, obj.mfcc = true, adds mfcc to the list of enabled features.

Determine Settable Parameters of Individual Feature Extractors

Create an audioFeatureExtractor to extract the ERB spectrum.

aFE = audioFeatureExtractor(erbSpectrum=true)

aFE = 
  audioFeatureExtractor with properties:

   Properties
                     Window: [1024x1 double]
              OverlapLength: 512
                 SampleRate: 44100
                  FFTLength: []
    SpectralDescriptorInput: 'linearSpectrum'
        FeatureVectorLength: 43

   Enabled Features
     erbSpectrum

   Disabled Features
     linearSpectrum, melSpectrum, barkSpectrum, mfcc, mfccDelta, mfccDeltaDelta
     gtcc, gtccDelta, gtccDeltaDelta, spectralCentroid, spectralCrest, spectralDecrease
     spectralEntropy, spectralFlatness, spectralFlux, spectralKurtosis, spectralRolloffPoint, spectralSkewness
     spectralSlope, spectralSpread, pitch, harmonicRatio, zerocrossrate, shortTimeEnergy


   To extract a feature, set the corresponding property to true.
   For example, obj.mfcc = true, adds mfcc to the list of enabled features.

The second output argument from info is a struct that contains the settable parameters of the individual feature extractors and their current value.

[~,params] = info(aFE)

params = struct with fields:
    erbSpectrum: [1x1 struct]

params.erbSpectrum

ans = struct with fields:
                   NumBands: 43
             FrequencyRange: [0 22050]
    FilterBankNormalization: "bandwidth"
        WindowNormalization: 1
               SpectrumType: "power"
                   ApplyLog: 0

If you are using the default parameter values, then the parameters are dynamic and updated when properties they depend on are updated. For example, the default frequency range of the ERB filter bank and the default number of bandpass filters in the ERB filter bank depends on the sample rate. Decrease the sample rate of the audioFeatureExtractor object and then call info again.

aFE.SampleRate = 16e3;
[~,params] = info(aFE);
params.erbSpectrum

ans = struct with fields:
                   NumBands: 34
             FrequencyRange: [0 8000]
    FilterBankNormalization: "bandwidth"
        WindowNormalization: 1
               SpectrumType: "power"
                   ApplyLog: 0

You can modify the individual feature extractor parameters using setExtractorParameters. Set the number of bands to 40 and the spectrum type to "magnitude". Call info to confirm that the parameters are updated.

params.erbSpectrum.NumBands = 40;
params.erbSpectrum.SpectrumType = "magnitude";
setExtractorParameters(aFE,erbSpectrum=params.erbSpectrum)
[~,params] = info(aFE);
params.erbSpectrum

ans = struct with fields:
                   NumBands: 40
             FrequencyRange: [0 8000]
    FilterBankNormalization: "bandwidth"
        WindowNormalization: 1
               SpectrumType: "magnitude"
                   ApplyLog: 0

When you set individual feature extractor parameters, they remain at the set value until you set them to another value or return them to defaults. Return the sample rate of the audioFeatureExtractor object to its initial value and then call info. The parameters remain at their set value.

aFE.SampleRate = 44.1e3;

[~,params] = info(aFE);
params.erbSpectrum

ans = struct with fields:
                   NumBands: 40
             FrequencyRange: [0 8000]
    FilterBankNormalization: "bandwidth"
        WindowNormalization: 1
               SpectrumType: "magnitude"
                   ApplyLog: 0

To return parameters to their default values, call setExtractorParameters and specify no parameters.

setExtractorParameters(aFE,"erbSpectrum")
[~,params] = info(aFE);
params.erbSpectrum

ans = struct with fields:
                   NumBands: 43
             FrequencyRange: [0 22050]
    FilterBankNormalization: "bandwidth"
        WindowNormalization: 1
               SpectrumType: "power"
                   ApplyLog: 0

Input Arguments

aFE — Input object

audioFeatureExtractor object

audioFeatureExtractor object.

Output Arguments

idx — Mapping of requested features with output from extract

struct

Mapping of requested features with output from extract, returned as a struct with field names corresponding to individual feature extractors and field values corresponding to column indices.

params — Settable parameters of individual feature extractors

struct

Settable parameters of individual feature extractors, returned as a struct with field names corresponding to individual feature extractors and field values containing parameter specification structs. The parameter specification structs have field names corresponding to settable parameter names and field values corresponding to the current parameter setting.

Version History

Introduced in R2019b