spectralCentroid
Syntax
Description
specifies options using one or more name-value arguments.centroid
= spectralCentroid(x
,f
,Name=Value
)
spectralCentroid(___)
with no output arguments plots
the spectral centroid. You can specify an input combination from any of the previous syntaxes.
If the input is in the time domain, the spectral centroid is plotted against time.
If the input is in the frequency domain, the spectral centroid is plotted against frame number.
Examples
Spectral Centroid of Time-Domain Audio
Read in an audio file and calculate the centroid using default parameters.
[audioIn,fs] = audioread("Counting-16-44p1-mono-15secs.wav");
centroid = spectralCentroid(audioIn,fs);
Plot the centroid against time.
spectralCentroid(audioIn,fs);
Spectral Centroid of Frequency-Domain Audio Data
Read in an audio file and then buffer the signal into 30 ms frames with 20 ms overlap. Calculate the octave power spectrum using the poctave
function.
[audioIn,fs] = audioread("Counting-16-44p1-mono-15secs.wav"); audioBuffered = buffer(audioIn,round(fs*0.03),round(fs*0.02),"nodelay"); [p,cf] = poctave(audioBuffered,fs);
Calculate the centroid of the octave power spectrum over time.
centroid = spectralCentroid(p,cf);
Plot the centroid against the frame number.
spectralCentroid(p,cf)
Specify Nondefault Parameters
Read in an audio file.
[audioIn,fs] = audioread("Counting-16-44p1-mono-15secs.wav");
Calculate the centroid of the power spectrum over time. Calculate the centroid for 50 ms Hamming windows of data with 25 ms overlap. Use the range from 62.5 Hz to fs
/2 for the centroid calculation.
centroid = spectralCentroid(audioIn,fs, ... Window=hamming(round(0.05*fs)), ... OverlapLength=round(0.025*fs), ... Range=[62.5,fs/2]);
Plot the centroid against time.
spectralCentroid(audioIn,fs, ... Window=hamming(round(0.05*fs)), ... OverlapLength=round(0.025*fs), ... Range=[62.5,fs/2])
Calculate Spectral Centroid of Streaming Audio
Create a dsp.AudioFileReader
object to read in audio data frame-by-frame. Create a dsp.SignalSink
to log the spectral centroid calculation.
fileReader = dsp.AudioFileReader('Counting-16-44p1-mono-15secs.wav');
logger = dsp.SignalSink;
In an audio stream loop:
Read in a frame of audio data.
Calculate the spectral centroid for the frame of audio.
Log the spectral centroid for later plotting.
To calculate the spectral centroid for only a given input frame, specify a window with the same number of samples as the input, and set the overlap length to zero.
Plot the logged data.
while ~isDone(fileReader) audioIn = fileReader(); centroid = spectralCentroid(audioIn,fileReader.SampleRate, ... 'Window',hamming(size(audioIn,1)), ... 'OverlapLength',0); logger(centroid) end plot(logger.Buffer) ylabel('Centroid (Hz)')
If the input to your audio stream loop has a variable samples-per-frame, an inconsistent samples-per-frame with the analysis window size of spectralCentroid
, or if you want to calculate the spectral centroid for overlapped data, use dsp.AsyncBuffer
.
Create a dsp.AsyncBuffer
object, reset the logger, and release the file reader.
buff = dsp.AsyncBuffer; reset(logger) release(fileReader)
Specify that the spectral centroid is calculated for 50 ms frames with a 25 ms overlap.
fs = fileReader.SampleRate; samplesPerFrame = round(fs*0.05); samplesOverlap = round(fs*0.025); samplesPerHop = samplesPerFrame - samplesOverlap; win = hamming(samplesPerFrame); while ~isDone(fileReader) audioIn = fileReader(); write(buff,audioIn); while buff.NumUnreadSamples >= samplesPerHop audioBuffered = read(buff,samplesPerFrame,samplesOverlap); centroid = spectralCentroid(audioBuffered,fs, ... 'Window',win, ... 'OverlapLength',0); logger(centroid) end end release(fileReader)
Plot the logged data.
plot(logger.Buffer)
ylabel('Centroid (Hz)')
Input Arguments
x
— Input signal
column vector | matrix | 3-D array
Input signal, specified as a vector, matrix, or 3-D array. How the function
interprets x
depends on the shape of f
.
Data Types: single
| double
f
— Sample rate or frequency vector (Hz)
scalar | vector
Sample rate or frequency vector in Hz, specified as a scalar or vector,
respectively. How the function interprets x
depends on the shape
of f
:
If
f
is a scalar,x
is interpreted as a time-domain signal, andf
is interpreted as the sample rate. In this case,x
must be a real vector or matrix. Ifx
is specified as a matrix, the columns are interpreted as individual channels.If
f
is a vector,x
is interpreted as a frequency-domain signal, andf
is interpreted as the frequencies, in Hz, corresponding to the rows ofx
. In this case,x
must be a real L-by-M-by-N array, where L is the number of spectral values at given frequencies off
, M is the number of individual spectra, and N is the number of channels.The number of rows of
x
, L, must be equal to the number of elements off
.
Data Types: single
| double
Name-Value Arguments
Specify optional pairs of arguments as
Name1=Value1,...,NameN=ValueN
, where Name
is
the argument name and Value
is the corresponding value.
Name-value arguments must appear after other arguments, but the order of the
pairs does not matter.
Before R2021a, use commas to separate each name and value, and enclose
Name
in quotes.
Example: Window=hamming(256)
Note
The following name-value arguments apply if x
is a time-domain
signal. If x
is a frequency-domain signal, name-value arguments are
ignored.
Window
— Window applied in time domain
rectwin(round(f
*0.03))
(default) | vector
f
*0.03))Window applied in the time domain, specified as a real vector. The number of
elements in the vector must be in the range [1,
size(
]. The number of elements in the
vector must also be greater than x
,1)OverlapLength
.
Data Types: single
| double
OverlapLength
— Number of samples overlapped between adjacent windows
round(f
*0.02)
(default) | non-negative scalar
f
*0.02)Number of samples overlapped between adjacent windows, specified as an integer in
the range [0, size(
).Window
,1)
Data Types: single
| double
FFTLength
— Number of bins in DFT
numel(Window
)
(default) | positive scalar integer
Window
)Number of bins used to calculate the DFT of windowed input samples, specified as a
positive scalar integer. If unspecified, FFTLength
defaults to
the number of elements in the Window
.
Data Types: single
| double
Range
— Frequency range (Hz)
[0,f
/2]
(default) | two-element row vector
f
/2]Frequency range in Hz, specified as a two-element row vector of increasing real
values in the range [0, f
/2].
Data Types: single
| double
SpectrumType
— Spectrum type
"power"
(default) | "magnitude"
Spectrum type, specified as "power"
or
"magnitude"
:
"power"
–– The spectral centroid is calculated for the one-sided power spectrum."magnitude"
–– The spectral centroid is calculated for the one-sided magnitude spectrum.
Data Types: char
| string
Output Arguments
centroid
— Spectral centroid (Hz)
scalar | vector | matrix
Spectral centroid in Hz, returned as a scalar, vector, or matrix. Each row of
centroid
corresponds to the spectral centroid of a window of
x
. Each column of centroid
corresponds to an
independent channel.
Algorithms
The spectral centroid is calculated as described in [1]:
where
fk is the frequency in Hz corresponding to bin k.
sk is the spectral value at bin k.
b1 and b2 are the band edges, in bins, over which to calculate the spectral centroid.
References
[1] Peeters, G. "A Large Set of Audio Features for Sound Description (Similarity and Classification) in the CUIDADO Project." Technical Report; IRCAM: Paris, France, 2004.
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Version History
Introduced in R2019a
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