% 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.


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{\bf \large \sf Purpose}\\
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\begin{minipage}[t]{13.5cm}
Fast Mellin Transform.
\end{minipage}
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{\bf \large \sf Synopsis}\\
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\begin{verbatim}
[mellin,beta] = ffmt(x)
[mellin,beta] = ffmt(x,fmin,fmax)
[mellin,beta] = ffmt(x,fmin,fmax,N)
\end{verbatim}
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{\bf \large \sf Description}\\
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        {\ty ffmt} computes the Fast Mellin Transform of signal {\ty x}.\\
 
\hspace*{-.5cm}\begin{tabular*}{14cm}{p{1.5cm} p{8.5cm} c}
Name & Description & Default value\\
\hline
        {\ty x} & signal in time\\
        {\ty fmin, fmax} & respectively lower and upper frequency bounds of 
         the analyzed signal. These parameters fix the equivalent 
         frequency bandwidth (expressed in Hz). When unspecified, you
         have to enter them at the command line from the plot of the
         spectrum. {\ty fmin} and {\ty fmax} must be between 0 and 0.5\\     
        {\ty N} & number of analyzed voices. {\ty N} must be even &
	auto\footnote{This value, determined from {\ty fmin} and {\ty fmax}, is the 
	next-power-of-two of the minimum value checking the non-overlapping
	condition in the fast Mellin transform.}\\
\hline  {\ty mellin} & the {\ty N}-points Mellin transform of signal {\ty x}\\
        {\ty beta} & the {\ty N}-points Mellin variable\\ 
\hline
\end{tabular*}
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The Mellin transform is invariant in modulus to dilations, and decomposes
the signal on a basis of hyperbolic signals. This transform can be defined
as\,:
\[M_x(\beta)=\int_0^{+\infty} x(\nu)\ \nu^{j2\pi \beta-1}\ d\nu\]
where $x(\nu)$ is the Fourier transform of the analytic signal
corresponding to $x(t)$. The $\beta$-parameter can be interpreted as a {\it
hyperbolic modulation rate}, and has no dimension\,; it is called the {\it
Mellin's scale}. 

In the discrete case, the Mellin transform can be calculated rapidly using
a fast Fourier transform ({\ty fft}). The fast Mellin transform is  used,
for example, in the computation of the affine time-frequency distributions.
\end{minipage}

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{\bf \large \sf Example}
\begin{verbatim}
         sig=altes(128,0.05,0.45); 
         [mellin,beta]=ffmt(sig,0.05,0.5,128);
         plot(beta,real(mellin));
\end{verbatim}
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{\bf \large \sf See Also}\\
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\begin{minipage}[t]{13.5cm}
\begin{verbatim}
iffmt, fft, ifft.
\end{verbatim}
\end{minipage}
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{\bf \large \sf References}\\
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\begin{minipage}[t]{13.5cm}
[1] J. Bertrand, P. Bertrand, J-P. Ovarlez ``Discrete Mellin Transform for
Signal Analysis'' Proc IEEE-ICASSP, Albuquerque, NM USA, 1990.\\

[2] J-P. Ovarlez, J. Bertrand, P. Bertrand ``Computation of Affine
Time-Frequency Representations Using the Fast Mellin Transform'' Proc
IEEE-ICASSP, San Fransisco, CA USA, 1992.
\end{minipage}


