Manual Page - acgram(1)

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Manual Reference Pages  - ACGRAM (1)

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NAME

acgram - Autocorrelogram auditory image.

CONTENTS

Syntax
Description
Examples
Copyright

SYNTAX

acgram [arguments] [file]

DESCRIPTION

Short-time autocorrelation function applied to each row of input frames.
Output frames consist of row-wise autocorrelation coefficients.
The autocorrelation function (acf) is computed using the fft. Strictly
speaking this generates an autocovariance function, but an optional
normalization (dividing each coefficient by the zeroth coefficient) produces
the autocorrelation function.

The program expects to read an AIM header, and interprets input as one large
frame in column-wise format (eg output from genbmm, gennap, etc.), to be
divided into input frames, each to be processed as an autocorrelogram.
A new header is constructed, and each autocorrelogram frame is output in
row-wise format (eg as if output from gensai).

The input is divided into frames according to the given options.
The options ’start’ and ’length’ specify the input file.
The special option value length=max specifies all the input file from
the given start to its end.
The options ’width’ and ’frstep’ specify the input frames.
The width option is the framewidth of each input frame and the frstep
option is the frameshift between input frames in the input file.
The special option value width=max specifies the input framewidth as equal
to the given input file length, (and if this is also ’max’, then the
input framewidth is the remainder of the input file).

Most options in the input header are copied to the output header.
This enables options which are needed for the eventual display
to pass straight through. Some options are set so that they can override
the input header. For example, the display option is set on to enable
display even when input has display=off. The animate option can be set on
even when the input has animate=off.
Some parts of the header are changed for the output format:
(frames, frameshift, framewidth, frameheight, framebytes).

Each row of each input frame is padded with zeroes to the next
power of 2 larger than either the original input framewidth or twice the
max acf lag (whichever is the larger).
If necessary, extra padding can be enforced using the (silent) padding option
to add extra zeroes, padding to a larger power of 2.
The amount of extra padding is ’exponential’, expanding the basic size to:

( framewidth + padding ) * 2**n

where the padding option is n.

(n=0 by default, so that no extra padding is added. When n=1 then padding is
added to double the size, and when n=2 the size is quadrupled, etc.).

EXAMPLES

1. Autocorrelogram of a NAP, animated and normalized, with max lag 16ms:

gennap len=128ms output=stdout display=off file | acgram lag=16ms norm=on
anim=on > file.sai

gensai useprev=on headr=5 top=1000 file -(for landscape plot)

genspl useprev=on headr=5 top=1000 pensize=2 file -(for spiral plot)

2. Autocorrelogram of an SAI:

(gensai removes file.sai, so you must use some other name, eg foo.sai).

gensai len=64 pwidth=64 nwidth=0 output=stdout display=off file |
saitonap frame=3 | acgram lag=32ms frame=1 > foo.sai

gensai useprev=on top=1000 headr=5 mag=2 foo

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.

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