tfrstft.tex

STFT相关函数

% 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{tfrstft}
\hspace*{-1.6cm}{\Large \bf tfrstft}

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

{\bf \large \fontfamily{cmss}\selectfont Purpose}\\
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\begin{minipage}[t]{13.5cm}
Short time Fourier transform.
\end{minipage}
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{\bf \large \fontfamily{cmss}\selectfont Synopsis}\\
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\begin{minipage}[t]{13.5cm}
\begin{verbatim}
[tfr,t,f] = tfrstft(x)
[tfr,t,f] = tfrstft(x,t)
[tfr,t,f] = tfrstft(x,t,N)
[tfr,t,f] = tfrstft(x,t,N,h)
[tfr,t,f] = tfrstft(x,t,N,h,trace)
\end{verbatim}
\end{minipage}
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{\bf \large \fontfamily{cmss}\selectfont Description}\\
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        {\ty tfrstft} computes the short-time Fourier transform of a
        discrete-time signal {\ty x}. Its continuous expression writes
\[F_x(t,\nu;h) = \int_{-\infty}^{+\infty} x(u)\ h^*(u-t)\ e^{-j2\pi
\nu u}\ du\] where $h(t)$ is a {\it short time analysis window} localized
around $t=0$ and $\nu=0$.\\

\hspace*{-.5cm}\begin{tabular*}{14cm}{p{1.5cm} p{8cm} c}
Name & Description & Default value\\
\hline
        {\ty x}     & signal ({\ty Nx=length(x)}) \\
        {\ty t}     & time instant(s)          & {\ty (1:Nx)}\\
        {\ty N}     & number of frequency bins & {\ty Nx}\\
        {\ty h}     & smoothing window, {\ty h} being normalized so as to
                be  of unit energy.      & {\ty window(odd(N/4))}\\ 
        {\ty trace} & if nonzero, the progression of the algorithm is shown
                                         & {\ty 0}\\
     \hline {\ty tfr}   & time-frequency decomposition (complex values). The
                frequency axis is graduated from {\ty -0.5} to {\ty 0.5}\\
        {\ty f}     & vector of normalized frequencies\\

\hline
\end{tabular*}
\vspace*{.2cm}

When called without output arguments, {\ty tfrstft} runs {\ty tfrqview},
which displays the squared modulus of the short-time Fourier transform.
\end{minipage}

\newpage

{\bf \large \fontfamily{cmss}\selectfont Example}
\begin{verbatim}
         sig=[fmlin(128,0.05,.45);fmlin(128,0.35,.15)]; 
         tfr=tfrstft(sig);
         subplot(211); imagesc(abs(tfr(1:128,:))); axis('xy')
         subplot(212); imagesc(angle(tfr(1:128,:))); axis('xy')
\end{verbatim}
\vspace*{.5cm}

{\bf \large \fontfamily{cmss}\selectfont See Also}\\
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\begin{minipage}[t]{13.5cm}
all the {\ty tfr*} functions.
\end{minipage}
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{\bf \large \fontfamily{cmss}\selectfont References}\\
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[1] J. Allen, L. Rabiner ``A Unified Approach to Short-Time Fourier
Analysis and Synthesis'' Proc. of the IEEE, Vol. 65, No. 11, pp. 1558-64,
Nov. 1977.\\

[2] S. Nawab, T. Quatieri ``Short-Time Fourier Transform'', chapter in {\it
Advanced Topics in Signal Processing} J. Lim and A. Oppenheim
eds. Prentice Hall, Englewood Cliffs, NJ, 1988.
\end{minipage}