momttfr.tex

时频分析的工具包

% This is part of the TFTB Reference Manual.
% Copyright (C) 1996 CNRS (France) and Rice University (US).
% See the file refguide.tex for copying conditions.


\markright{momttfr}
\hspace*{-1.6cm}{\Large \bf momttfr}

\vspace*{-.4cm}
\hspace*{-1.6cm}\rule[0in]{16.5cm}{.02cm}
\vspace*{.2cm}



{\bf \large \fontfamily{cmss}\selectfont Purpose}\\
\hspace*{1.5cm}
\begin{minipage}[t]{13.5cm}
Time moments of a time-frequency representation.
\end{minipage}
\vspace*{.5cm}


{\bf \large \fontfamily{cmss}\selectfont Synopsis}\\
\hspace*{1.5cm}
\begin{minipage}[t]{13.5cm}
\begin{verbatim}
[fm,B2] = momttfr(tfr,method)
[fm,B2] = momttfr(tfr,method,fbmin)
[fm,B2] = momttfr(tfr,method,fbmin,fbmax)
[fm,B2] = momttfr(tfr,method,fbmin,fbmax,freqs)
\end{verbatim}
\end{minipage}
\vspace*{.5cm}


{\bf \large \fontfamily{cmss}\selectfont Description}\\
\hspace*{1.5cm}
\begin{minipage}[t]{13.5cm}
        {\ty momttfr} computes the time moments of order 1 and 2 of a
        time-frequency representation\,:
\[f_m(t) = \frac{1}{E}\ \int_{-\infty}^{+\infty} f\ \mbox{tfr}(t,f)\ df\ \
;\ \ B^2(t) = \frac{1}{E}\ \int_{-\infty}^{+\infty} f^2\ \mbox{tfr}(t,f)\ df -
f_m(t)^2.\] 

\hspace*{-.5cm}\begin{tabular*}{14cm}{p{1.5cm} p{8.5cm} c}
Name & Description & Default value\\
\hline
        {\ty tfr}   & time-frequency representation (size {\ty (N,M)})\\
        {\ty method}& chosen representation (name of the corresponding M-file). \\ 
        {\ty fbmin} & smallest frequency bin & {\ty 1}\\
        {\ty fbmax} & highest  frequency bin & {\ty M}\\
        {\ty freqs} & true frequency of each frequency bin. {\ty freqs} must be of
                length {\ty fbmax-fbmin+1} & auto\footnote{{\ty freqs} goes
		from 0 to 0.5 or from -0.5 to 0.5 depending on {\ty method}.}\\
 \hline {\ty fm}    & averaged frequency     (first order moment)\\
        {\ty B2}    & squared frequency bandwidth (second order moment)\\

\hline
\end{tabular*}

\end{minipage}
\vspace*{1cm}


{\bf \large \fontfamily{cmss}\selectfont Examples}\\
\hspace*{1.5cm}
\begin{minipage}[t]{13.5cm}
\begin{verbatim}
         sig=fmlin(200,0.1,0.4); tfr=tfrwv(sig);
         [fm,B2]=momttfr(tfr,'tfrwv'); 
         subplot(211); plot(fm); subplot(212); plot(B2);
         freqs=linspace(0,99/200,100); tfr=tfrsp(sig); 
         [fm,B2]=momttfr(tfr,'tfrsp',1,100,freqs); 
         subplot(211); plot(fm); subplot(212); plot(B2);
\end{verbatim}
\end{minipage}

%\newpage

\hspace*{1.5cm}
\begin{minipage}[t]{13.5cm}
The first order moment represents an estimation of the instantaneous
frequency, and the second order moment the variance of this estimator. We
can see that the estimation is better around the time center position than
at the edges of the observation interval. Besides, the second estimator
(using the spectrogram) has a lower variance than the first one (using the
Wigner-Ville distribution), but presents an important bias.
\end{minipage}
\vspace*{1cm}


{\bf \large \fontfamily{cmss}\selectfont See Also}\\
\hspace*{1.5cm}
\begin{minipage}[t]{13.5cm}
\begin{verbatim}
momftfr, margtfr.
\end{verbatim}
\end{minipage}