view man/man1/filt1.1 @ 0:5242703e91d3 tip

Initial checkin for AIM92 aimR8.2 (last updated May 1997).

.TH FILT1 1 "1 September 1993"

.SH NAME
filt1 \- 1st order LP filter using an exponential smoother.

.SH SYNTAX 
filt1 [options] [file]

.SH DESCRIPTION
A recursive "leaky integrator" 1st order low-pass filter which is a shifting
exponential window which decays into the past values.

.SH OPTIONS

1. tc

The time-constant parameter which controls the rate of decay and so the
size of the exponential window. For a given time constant of T seconds:

.nf
	0.7T secs   is the window half--life.
	4.6T secs   is 99% of the window's life.
.fi

When the time-constant parameter is given with time units (s or ms) then
it is converted to a decay constant using  a = exp(-Ts/T),
where Ts is the sample interval in seconds from the given `samplerate' option,
and T  is decay time-constant in seconds.
Otherwise the time-constant parameter is taken to be the decay constant directly.

With decay constant a=1 there is infinite memory because it does not decay.
With 0 < a < 1 there is a finite decaying memory.
The smaller `a', the smaller the memory (it decays faster).
With a = 0 the filter output is identical with its input.

2. de

Two optional difference equations are provided which repsectively compute
a recursive sum (when "de=sum") and mean (when "de=mean").
The n'th recursive update is respectively:

.nf
	y[n] = a.y[n-1] + x[n]                recursive sum
	y[n] = a.y[n-1] + (1-a).x[n]          recursive mean
.fi

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

.SH "SEE ALSO"
options smooth

.SH COPYRIGHT
.LP
Copyright (c) Applied Psychology Unit, Medical Research Council, 1995
.LP
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.
.LP
The MRC makes no representations about the suitability of this 
software for any purpose.  It is provided "as is" without express or 
implied warranty.
.LP
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.