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racf


Manual Reference Pages  - RACF (1)

NAME

racf - recursive autocorrelation function of contiguous frames.

CONTENTS

Syntax
Description
Copyright

SYNTAX

racf [arguments] [file]

DESCRIPTION

Autocorrelation function using a recursive "leaky integrator" filter. For the m’th lag, the n’th recursive update is:

      y[n] = a.y[n-1] + (1-a).f[n].f[n-m]

where decay constant a = exp(-Ts/T), Ts is the sample interval in seconds, and T is the decay time constant in seconds.

The recursion computes the mean value of the product f[n].f[n-m] within an exponential window which weights past values. The window width parameter (eg. corresponding with the width of the fft analysis window) is the time constant parameter. The half life of the exponential window is given by -T.ln(0.5) = 0.693T ie. for a given time constant, T secs, the window decays to half of its current value in a period of 0.693T secs. Similarly, the window decays by 99% of its initial value in about 4.6T secs. So T can be set to accomodate an expected period.

The routine generates the autocovariance function. An optional normalization (dividing each coefficient by the zeroth coefficient) produces the autocorrelation function, (and this is then scaled up to the range [0-1000]).

The output framewidth is the given maximum acf lag.

SEE ALSO

options acf acgram

COPYRIGHT

Copyright (c) Applied Psychology Unit, Medical Research Council, 1995

Permission to use, copy, modify, and distribute this software without fee is hereby granted for research purposes, provided that this copyright notice appears in all copies and in all supporting documentation, and that the software is not redistributed for any fee (except for a nominal shipping charge). Anyone wanting to incorporate all or part of this software in a commercial product must obtain a license from the Medical Research Council.

The MRC makes no representations about the suitability of this software for any purpose. It is provided "as is" without express or implied warranty.

THE MRC DISCLAIMS ALL WARRANTIES WITH REGARD TO THIS SOFTWARE, INCLUDING ALL IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS, IN NO EVENT SHALL THE A.P.U. BE LIABLE FOR ANY SPECIAL, INDIRECT OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.


SunOS 5.6 RACF (1) 1 September 1993
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