melSpectrogram

Mel spectrogram

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Syntax

S = melSpectrogram(audioIn,fs)

S = melSpectrogram(audioIn,fs,Name,Value)

[S,F,T] = melSpectrogram(___)

melSpectrogram(___)

Description

example

S = melSpectrogram(audioIn,fs) returns the mel spectrogram of the audio input at sample rate fs. The function treats columns of the input as individual channels.

example

S = melSpectrogram(audioIn,fs,Name,Value) specifies options using one or more Name,Value pair arguments.

example

[S,F,T] = melSpectrogram(___) returns the center frequencies of the bands in Hz and the location of each window of data in seconds. The location corresponds to the center of each window. You can use this output syntax with any of the previous input syntaxes.

example

melSpectrogram(___) plots the mel spectrogram on a surface in the current figure.

Examples

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Calculate Mel Spectrogram

Open Live Script

Use the default settings to calculate the mel spectrogram for an entire audio file. Print the number of bandpass filters in the filter bank and the number of frames in the mel spectrogram.

[audioIn,fs] = audioread('Counting-16-44p1-mono-15secs.wav');

S = melSpectrogram(audioIn,fs);

[numBands,numFrames] = size(S);
fprintf("Number of bandpass filters in filterbank: %d\n",numBands)

Number of bandpass filters in filterbank: 32

fprintf("Number of frames in spectrogram: %d\n",numFrames)

Number of frames in spectrogram: 1551

Plot the mel spectrogram.

melSpectrogram(audioIn,fs)

Calculate Mel Spectrums of 2048-Point Windows

Open Live Script

Calculate the mel spectrums of 2048-point periodic Hann windows with 1024-point overlap. Convert to the frequency domain using a 4096-point FFT. Pass the frequency-domain representation through 64 half-overlapped triangular bandpass filters that span the range 62.5 Hz to 8 kHz.

[audioIn,fs] = audioread('FunkyDrums-44p1-stereo-25secs.mp3');

S = melSpectrogram(audioIn,fs, ...
                   'Window',hann(2048,'periodic'), ...
                   'OverlapLength',1024, ...
                   'FFTLength',4096, ...
                   'NumBands',64, ...
                   'FrequencyRange',[62.5,8e3]);

Call melSpectrogram again, this time with no output arguments so that you can visualize the mel spectrogram. The input audio is a multichannel signal. If you call melSpectrogram with a multichannel input and with no output arguments, only the first channel is plotted.

melSpectrogram(audioIn,fs, ...
               'Window',hann(2048,'periodic'), ...
               'OverlapLength',1024, ...
               'FFTLength',4096, ...
               'NumBands',64, ...
               'FrequencyRange',[62.5,8e3])

Get Filter Bank Center Frequencies and Analysis Window Time Instants

Open Live Script

melSpectrogram applies a frequency-domain filter bank to audio signals that are windowed in time. You can get the center frequencies of the filters and the time instants corresponding to the analysis windows as the second and third output arguments from melSpectrogram.

Get the mel spectrogram, filter bank center frequencies, and analysis window time instants of a multichannel audio signal. Use the center frequencies and time instants to plot the mel spectrogram for each channel.

[audioIn,fs] = audioread('AudioArray-16-16-4channels-20secs.wav');

[S,cF,t] = melSpectrogram(audioIn,fs);

S = 10*log10(S+eps); % Convert to dB for plotting

for i = 1:size(S,3)
    figure(i)
    surf(t,cF,S(:,:,i),'EdgeColor','none');
    xlabel('Time (s)')
    ylabel('Frequency (Hz)')
    view([0,90])
    title(sprintf('Channel %d',i))
    axis([t(1) t(end) cF(1) cF(end)])
end

Input Arguments

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`audioIn` — Audio input
column vector | matrix

Audio input, specified as a column vector or matrix. If specified as a matrix, the function treats columns as independent audio channels.

Data Types: single | double

`fs` — Input sample rate (Hz)
positive scalar

Input sample rate in Hz, specified as a positive scalar.

Data Types: single | double

Name-Value Pair Arguments

Specify optional comma-separated pairs of Name,Value arguments. Name is the argument name and Value is the corresponding value. Name must appear inside quotes. You can specify several name and value pair arguments in any order as Name1,Value1,...,NameN,ValueN.

Example: 'WindowLength',1024

`'Window'` — Window applied in time domain
`hamming(round(fs*0.3),'periodic')` (default) | vector

Window applied in time domain, specified as the comma-separated pair consisting of 'Window' and a real vector. The number of elements in the vector must be in the range [1,size(audioIn,1)]. The number of elements in the vector must also be greater than OverlapLength.

Data Types: single | double

`'OverlapLength'` — Analysis window overlap length (samples)
`round(0.02*fs)` (default) | integer in the range `[0, (WindowLength - 1)]`

Analysis window overlap length in samples, specified as the comma-separated pair consisting of 'OverlapLength' and an integer in the range [0, (WindowLength - 1)].

Data Types: single | double

`'FFTLength'` — Number of DFT points
`WindowLength` (default) | positive integer

Number of points used to calculate the DFT, specified as the comma-separated pair consisting of 'FFTLength' and a positive integer greater than or equal to WindowLength. If unspecified, FFTLength defaults to WindowLength.

Data Types: single | double

`'NumBands'` — Number of mel bandpass filters
`32` (default) | positive integer

Number of mel bandpass filters, specified as the comma-separated pair consisting of 'NumBands' and a positive integer.

Data Types: single | double

`'FrequencyRange'` — Frequency range over which to compute mel spectrogram (Hz)
`[0 fs/2]` (default) | two-element row vector

Frequency range over which to compute the mel spectrogram in Hz, specified as the comma-separated pair consisting of 'FrequencyRange' and a two-element row vector of monotonically increasing values in the range [0, fs/2].

Data Types: single | double

`'SpectrumType'` — Type of mel spectrogram
`'power'` (default) | `'magnitude'`

Type of mel spectrogram, specified as the comma-separated pair consisting of 'SpectrumType' and 'power' or 'magnitude'.

Data Types: char | string

`'WindowNormalization'` — Apply window normalization
`true` (default) | `false`

Apply window normalization, specified as the comma-separated pair consisting of 'WindowNormalization' and true or false. When WindowNormalization is set to true, the power (or magnitude) in the mel spectrogram is normalized to remove the power (or magnitude) of the time domain Window.

Data Types: char | string

`'FilterBankNormalization'` — Type of filter bank normalization
`'bandwidth'` (default) | `'area'` | `'none'`

Type of filter bank normalization, specified as the comma-separated pair consisting of 'FilterBankNormalization' and 'bandwidth', 'area', or 'none'.

Data Types: char | string

Output Arguments

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`S` — Mel spectrogram
column vector | matrix | 3-D array

Mel spectrogram, returned as a column vector, matrix, or 3-D array. The dimensions of S are L-by-M-by-N, where:

L is the number of frequency bins in each mel spectrum. NumBands and fs determine L.
M is the number of frames the audio signal is partitioned into. size(audioIn,1), WindowLength, and OverlapLength determine M.
N is the number of channels such that N = size(audioIn,2).

Trailing singleton dimensions are removed from the output S.

Data Types: single | double

`F` — Center frequencies of mel bandpass filters (Hz)
row vector

Center frequencies of mel bandpass filters in Hz, returned as a row vector with length size(S,1).

Data Types: single | double

`T` — Location of each window of audio (s)
row vector

Location of each analysis window of audio in seconds, returned as a row vector length size(S,2). The location corresponds to the center of each window.

Data Types: single | double

Algorithms

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The melSpectrogram function follows the general algorithm to compute a mel spectrogram as described in [1].

In this algorithm, the audio input is first buffered into frames of numel(Window) number of samples. The frames are overlapped by OverlapLength number of samples. The specified Window is applied to each frame, and then the frame is converted to frequency-domain representation with FFTLength number of points. The frequency-domain representation can be either magnitude or power, specified by SpectrumType. If WindowNormalization is set to true, the spectrum is normalized by the window. Each frame of the frequency-domain representation passes through a mel filter bank. The spectral values output from the mel filter bank are summed, and then the channels are concatenated so that each frame is transformed to a NumBands-element column vector.

Filter Bank Design

The mel filter bank is designed as half-overlapped triangular filters equally spaced on the mel scale. NumBands controls the number of mel bandpass filters. FrequencyRange controls the band edges of the first and last filters in the mel filter bank. FilterBankNormalization specifies the type of normalization applied to the individual bands.

Compatibility Considerations

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`WindowLength` will be removed in a future release

Behavior change in future release

The WindowLength parameter will be removed from the melSpectrogram function in a future release. Use the Window parameter instead.

In releases prior to R2020b, you could only specify the length of a time-domain window. The window was always designed as a periodic Hamming window. You can replace instances of the code

S = melSpectrogram(audioin,fs,'WindowLength',1024);

With this code:

S = melSpectrogram(audioIn,fs,'Window',hamming(1024,'periodic'));

References

[1] Rabiner, Lawrence R., and Ronald W. Schafer. Theory and Applications of Digital Speech Processing. Upper Saddle River, NJ: Pearson, 2010.

Documentation

melSpectrogram

Syntax

Description

Examples

Calculate Mel Spectrogram

Calculate Mel Spectrums of 2048-Point Windows

Get Filter Bank Center Frequencies and Analysis Window Time Instants

Input Arguments

`audioIn` — Audio input
column vector | matrix

`fs` — Input sample rate (Hz)
positive scalar

Name-Value Pair Arguments

`'Window'` — Window applied in time domain
`hamming(round(fs*0.3),'periodic')` (default) | vector

`'OverlapLength'` — Analysis window overlap length (samples)
`round(0.02*fs)` (default) | integer in the range `[0, (WindowLength - 1)]`

`'FFTLength'` — Number of DFT points
`WindowLength` (default) | positive integer

`'NumBands'` — Number of mel bandpass filters
`32` (default) | positive integer

`'FrequencyRange'` — Frequency range over which to compute mel spectrogram (Hz)
`[0 fs/2]` (default) | two-element row vector

`'SpectrumType'` — Type of mel spectrogram
`'power'` (default) | `'magnitude'`

`'WindowNormalization'` — Apply window normalization
`true` (default) | `false`

`'FilterBankNormalization'` — Type of filter bank normalization
`'bandwidth'` (default) | `'area'` | `'none'`

Output Arguments

`S` — Mel spectrogram
column vector | matrix | 3-D array

`F` — Center frequencies of mel bandpass filters (Hz)
row vector

`T` — Location of each window of audio (s)
row vector

Algorithms

Filter Bank Design

Compatibility Considerations

`WindowLength` will be removed in a future release

References

Extended Capabilities

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

GPU Code Generation
Generate CUDA® code for NVIDIA® GPUs using GPU Coder™.

GPU Arrays
Accelerate code by running on a graphics processing unit (GPU) using Parallel Computing Toolbox™.

See Also

Topics

Audio Toolbox Documentation

Support

Documentation

melSpectrogram

Syntax

Description

Examples

Calculate Mel Spectrogram

Calculate Mel Spectrums of 2048-Point Windows

Get Filter Bank Center Frequencies and Analysis Window Time Instants

Input Arguments

audioIn — Audio input column vector | matrix

fs — Input sample rate (Hz) positive scalar

Name-Value Pair Arguments

'Window' — Window applied in time domain hamming(round(fs*0.3),'periodic') (default) | vector

'OverlapLength' — Analysis window overlap length (samples) round(0.02*fs) (default) | integer in the range [0, (WindowLength - 1)]

'FFTLength' — Number of DFT points WindowLength (default) | positive integer

'NumBands' — Number of mel bandpass filters 32 (default) | positive integer

'FrequencyRange' — Frequency range over which to compute mel spectrogram (Hz) [0 fs/2] (default) | two-element row vector

'SpectrumType' — Type of mel spectrogram 'power' (default) | 'magnitude'

'WindowNormalization' — Apply window normalization true (default) | false

'FilterBankNormalization' — Type of filter bank normalization 'bandwidth' (default) | 'area' | 'none'

Output Arguments

S — Mel spectrogram column vector | matrix | 3-D array

F — Center frequencies of mel bandpass filters (Hz) row vector

T — Location of each window of audio (s) row vector

Algorithms

Filter Bank Design

Compatibility Considerations

WindowLength will be removed in a future release

References

Extended Capabilities

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

GPU Code Generation Generate CUDA® code for NVIDIA® GPUs using GPU Coder™.

GPU Arrays Accelerate code by running on a graphics processing unit (GPU) using Parallel Computing Toolbox™.

See Also

Topics

Audio Toolbox Documentation

Support

`audioIn` — Audio input
column vector | matrix

`fs` — Input sample rate (Hz)
positive scalar

`'Window'` — Window applied in time domain
`hamming(round(fs*0.3),'periodic')` (default) | vector

`'OverlapLength'` — Analysis window overlap length (samples)
`round(0.02*fs)` (default) | integer in the range `[0, (WindowLength - 1)]`

`'FFTLength'` — Number of DFT points
`WindowLength` (default) | positive integer

`'NumBands'` — Number of mel bandpass filters
`32` (default) | positive integer

`'FrequencyRange'` — Frequency range over which to compute mel spectrogram (Hz)
`[0 fs/2]` (default) | two-element row vector

`'SpectrumType'` — Type of mel spectrogram
`'power'` (default) | `'magnitude'`

`'WindowNormalization'` — Apply window normalization
`true` (default) | `false`

`'FilterBankNormalization'` — Type of filter bank normalization
`'bandwidth'` (default) | `'area'` | `'none'`

`S` — Mel spectrogram
column vector | matrix | 3-D array

`F` — Center frequencies of mel bandpass filters (Hz)
row vector

`T` — Location of each window of audio (s)
row vector

`WindowLength` will be removed in a future release

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

GPU Code Generation
Generate CUDA® code for NVIDIA® GPUs using GPU Coder™.

GPU Arrays
Accelerate code by running on a graphics processing unit (GPU) using Parallel Computing Toolbox™.