dspdata.msspectrum

Mean-square (power) spectrum

Syntax

Hmss = dspdata.msspectrum(Data) Hmss = dspdata.msspectrum(Data,Frequencies) Hmss = dspdata.msspectrum(...,'Fs',Fs) Hmss = dspdata.msspectrum(...,'SpectrumType',SpectrumType) Hmss = dspdata.msspectrum(...,'CenterDC',flag)

Description

Note

The use of dspdata.msspectrum is not recommended. Use periodogram or pwelch instead.

The mean-squared spectrum (MSS) is intended for discrete spectra. Unlike the power spectral density (PSD), the peaks in the MSS reflect the power in the signal at a given frequency. The MSS of a signal is the Fourier transform of that signal's autocorrelation.

Hmss = dspdata.msspectrum(Data) uses the mean-square (power) spectrum data contained in Data, which can be in the form of a vector or a matrix, where each column is a separate set of data. Default values for other properties of the object are as follows:

Property	Default Value	Description
Name	`'Mean-square Spectrum'`	Read-only character vector
`Frequencies`	`[]` type `double`	Vector of frequencies at which the spectrum is evaluated. The range of this vector depends on the `SpectrumType` value. For a one-sided spectrum, the default range is [0, π) or [0, `Fs`/2) for odd length, and [0, π] or [0, `Fs`/2] for even length, if `Fs` is specified. For a two-sided spectrum, it is [0, 2π) or [0, `Fs`). The length of the `Frequencies` vector must match the length of the columns of `Data`. If you do not specify `Frequencies`, a default vector is created. If one-sided is selected, then the whole number of FFT points (nFFT) for this vector is assumed to be even. If `onesided` is selected and you specify `Frequencies`, the last frequency point is compared to the next-to-last point and to pi (or `Fs`/2, if `Fs` is specified). If the last point is closer to pi (or `Fs`/2) than it is to the previous point, nFFT is assumed to be even. If it is closer to the previous point, nFFT is assumed to be odd.
`Fs`	`'Normalized'`	Sampling frequency, which is `'Normalized'` if `NormalizedFrequency` is `true`. If `NormalizedFrequency` is `false` `Fs` defaults to `1` Hz.
`SpectrumType`	`'Onesided'`	Nyquist interval over which the spectral density is calculated. Valid values are `'Onesided'` and `'Twosided'`. See the `onesided` and `twosided` methods in `dspdata` for information on changing this property. The interval for `Onesided` is [0 π) or [0 π] depending on the number of FFT points, and for `Twosided` the interval is [0 2π).
`NormalizedFrequency`	`true`	Whether the frequency is normalized (`true`) or not (`false`). This property is set automatically at construction time based on `Fs`. If `Fs` is specified, `NormalizedFrequency` is set to `false`. See the `normalizefreq` method in `dspdata` for information on changing this property.

Hmss = dspdata.msspectrum(Data,Frequencies) uses the mean–square spectrum data contained in Data and Frequencies vectors.

Hmss = dspdata.msspectrum(...,'Fs',Fs) uses the sampling frequency Fs. Specifying Fs uses a default set of linear frequencies (in Hz) based on Fs and sets NormalizedFrequency to false.

Hmss = dspdata.msspectrum(...,'SpectrumType',SpectrumType) uses SpectrumType to specify the interval over which the mean-square spectrum was calculated. For data that ranges from [0 π) or [0 π], set the SpectrumType to onesided; for data that ranges from [0 2π), set the SpectrumType to twosided.

Hmss = dspdata.msspectrum(...,'CenterDC',flag) uses the value of flag to indicate whether the zero-frequency (DC) component is centered. If flag is true, it indicates that the DC component is in the center of the two-sided spectrum. Set the flag to false if the DC component is on the left edge of the spectrum.

Methods

Methods provide ways of performing functions directly on your dspdata object without having to specify the parameters again. You can apply a method directly on the variable you assigned to your dspdata.msspectrum object. You can use the following methods with a dspdata.msspectrum object.

centerdc
normalizefreq
onesided
plot
sfdr
twosided

For example, to normalize the frequency and set the NormalizedFrequency parameter to true, use

Hmss = normalizefreq(Hs)

For detailed information on using the methods and plotting the spectrum, see the dspdata reference page.

Examples

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Mean-Square Spectrum of Sinusoids

Open Live Script

Create a signal consisting of two sinusoids in additive noise.

Fs = 32e3;
t = 0:1/Fs:1-1/Fs;
x = cos(2*pi*t*1.24e3)+cos(2*pi*t*10e3)+randn(size(t));

Compute the one-sided PSD estimate of the signal. Use the result to construct a dspdata object. Plot the mean-square spectrum.

P = periodogram(x,[],[],Fs);

Hmss = dspdata.msspectrum(P,'Fs',Fs,'spectrumtype','onesided'); 

plot(Hmss)

Figure contains an axes object. The axes object with title Mean-Square Spectrum, xlabel Frequency (kHz), ylabel Power (dB) contains an object of type line.

Version History

Introduced before R2006a