dspdata.pseudospectrum (Signal Processing Toolbox)

Pseudospectrum dspdata object

Syntax

Hps = dspdata.pseudospectrum(Data)
Hps = dspdata.pseudospectrum(Data,Frequencies)
Hps = dspdata.pseudospectrum(...,'Fs',Fs)
Hps = dspdata.pseudospectrum(...,'SpectrumRange',SpectrumRange)
Hps = dspdata.pseudospectrum(...,'CenterDC',flag)

Description

A pseudospectrum is an indicator of the presence of sinusoidal components in a signal.

Hps = dspdata.pseudospectrum(Data) uses the pseudospsectrum 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:

.

Property
Default Value
Description

Name
'Pseudospectrum'
Read-only string

Frequencies
[]
type double
Vector of frequencies at which the power spectral density is evaluated. The range of this vector depends on the SpectrumRange value. For half, the default range is [0, pi) or [0, Fs/2) for odd length, and [0, pi] or [0, Fs/2] for even length, if Fs is specified. For whole, it is [0, 2pi) or [0, Fs).

If you do not specify Frequencies, a default vector is created. If half the Nyquist range is selected, then the whole number of FFT points (nFFT) for this vector is assumed to be even.

If half the Nyquist range 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.

The length of the Frequencies vector must match the length of the columns of Data.

Fs
`Normalized'
Sampling frequency, which is 'Normalized' if NormalizedFrequency is true. If NormalizedFrequency is false Fs defaults to 1.

SpectrumRange
'Half'
Nyquist interval over which the pseudospectrum is calculated. Valid values are 'Half' and 'Whole'. See the half and whole methods in dspdata for information on changing this property.

The interval for Half is [0 pi) or [0 pi] depending on the number of FFT points, and for Whole the interval is [0 2pi).

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.

Property	Default Value	Description
Name	'Pseudospectrum'	Read-only string
`Frequencies`	`[]` type `double`	Vector of frequencies at which the power spectral density is evaluated. The range of this vector depends on the `SpectrumRange` value. For half, the default range is [0, pi) or [0, `Fs`/2) for odd length, and [0, pi] or [0, `Fs`/2] for even length, if `Fs` is specified. For whole, it is [0, 2pi) or [0, `Fs`). If you do not specify `Frequencies`, a default vector is created. If half the Nyquist range is selected, then the whole number of FFT points (nFFT) for this vector is assumed to be even. If `half` the Nyquist range 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. The length of the `Frequencies` vector must match the length of the columns of `Data`.
`Fs`	`Normalized'	Sampling frequency, which is `'Normalized'` if `NormalizedFrequency` is `true`. If `NormalizedFrequency` is `false` `Fs` defaults to `1`.
`SpectrumRange`	`'Half'`	Nyquist interval over which the pseudospectrum is calculated. Valid values are `'Half'` and `'Whole'`. See the `half` and `whole` methods in `dspdata` for information on changing this property. The interval for `Half` is [0 pi) or [0 pi] depending on the number of FFT points, and for `Whole` the interval is [0 2pi).
`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.

Hps = dspdata.pseudospectrum(Data,Frequencies) uses the pseudospectrum estimation data contained in the Data and Frequencies vectors.

Hps = dspdata.pseudospectrum(...,'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.

Hps = dspdata.pseudospectrum...,'SpectrumRange',SpectrumRange) uses the SpectrumRange string to specify the interval over which the pseudospectrum was calculated. For data that ranges from [0 pi) or [0 pi], set the SpectrumRange to half; for data that ranges from [0 2pi), set the the SpectrumRange to whole.

Hps = dspdata.pseudospectrum(...,'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 whole Nyquist range 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. You can apply a method directly on the variable you assigned to your dspdata.pseudospectrum object. You can use the following methods with a dspdata.pseudospectrum object.

centerdc
halfrange
normalizefreq
plot
wholerange

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

```
Hps = normalizefreq(Hps)
```

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

Examples

Storing and Plotting Pseudospectrum Data

Use eigenanalysis to estimate the pseudospectrum of a noisy sinusoidal signal with two frequency components. Then store the results in a pseudospectrum data object and plot it.

Fs = 32e3;
t  = 0:1/Fs:2.96; 
x = cos(2*pi*t*1.24e3) + cos(2*pi*t*10e3) + randn(size(t)); 
P = pmusic(x,4);
hps = dspdata.pseudospectrum(P,'Fs',Fs); % Create data object.
plot(hps);                          % Plot the pseudospectrum.

dspdata.psd dspfwiz