spectrum.mtm (Signal Processing Toolbox)

Thompson multitaper spectrum

Syntax

Hs = spectrum.mtm
Hs = spectrum.mtm(TimeBW)
Hs = spectrum.mtm(DPSS,Concentrations)
Hs = spectrum.mtm(...,CombineMethod)
Hs = spectrum.mtm(...,FFTLength)

Description

Hs = spectrum.mtm returns a default Thompson multitaper spectrum object, Hs that defines the parameters for the Thompson multitaper spectral estimation algorithm, which uses a linear or nonlinear combination of modified periodograms. The periodograms are computed using a sequence of orthogonal tapers (windows in the frequency domain) specified from discrete prolate spheroidal sequences (dpss). This object uses the following default values:

Property Name
Default Value
Description

TimeBW
4
Product of time and bandwidth for the discrete prolate spheroidal sequences (or Slepian sequences) used as data windows

CombineMethod
'adaptive'
Algorithm for combining the individual spectral estimates. Valid values are
'adaptive'--adaptive (nonlinear)
'unity'--unity weights (linear)
'eigenvector'--Eigenvalue weights (linear)

FFTlength
'NextPow2'
String defining how the number of FFT points is determined. The default is the next power of 2 that is greater than the input length. Other valid values are: 'InputLength' and 'UserDefined'. InputLength uses the length of the input signal as the FFT length. UserDefined uses the value provided via a psd method or dspopts object. See dspopts for an example.

Property Name	Default Value	Description
TimeBW	`4`	Product of time and bandwidth for the discrete prolate spheroidal sequences (or Slepian sequences) used as data windows
CombineMethod	`'adaptive'`	Algorithm for combining the individual spectral estimates. Valid values are `'adaptive'`--adaptive (nonlinear) `'unity'`--unity weights (linear) `'eigenvector'`--Eigenvalue weights (linear)
FFTlength	'NextPow2'	String defining how the number of FFT points is determined. The default is the next power of 2 that is greater than the input length. Other valid values are: `'InputLength'` and `'UserDefined'`. `InputLength` uses the length of the input signal as the FFT length. `UserDefined` uses the value provided via a `psd` method or `dspopts` object. See `dspopts` for an example.

Hs = spectrum.mtm(TimeBW) returns a spectrum object, Hs with the specified time-bandwidth product.

Hs = spectrum.mtm(DPSS,Concentrations) returns a spectrum object, Hs with the specified dpss data tapers and their concentrations.

Note You can either specify the time-bandwidth product (TimeBW) or the DPSS data tapers and their Concentrations. See dpss and pmtm for more information.

Hs = spectrum.mtm(...,CombineMethod) returns a spectrum object, Hs, with the specified method for combining the spectral estimates. Refer to the table above for valid CombineMethod values.

Hs = spectrum.mtm(...,FFTLength) returns a spectrum object, Hs with the specified way of determining the FFTLength. Refer to the table above for valid FFTLength values.

Examples

Define a cosine of 200 Hz, add noise and view its power spectral density using the Thompson multitaper algorithm with a time-bandwidth product of 3.5.

Fs=1000;
t=0:1/Fs:.3;
x=cos(2*pi*t*200)+randn(size(t));
Hs=spectrum.mtm(3.5);
psd(Hs,x,'Fs',Fs)

The above example could be done by specifying the data tapers and concentrations instead of the time-bandwidth product.

Fs=1000;
t=0:1/Fs:.3;
x=cos(2*pi*t*200)+randn(size(t));
[e,v]=dpss(length(x),3.5);
Hs=spectrum.mtm(e,v);
psd(Hs,x,'Fs',Fs)

spectrum.mcov spectrum.music