NAME

acgram - Autocorrelogram auditory image.

CONTENTS

Syntax
Description
Examples
Copyright

acgram [arguments] [file]

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. Strictlyspeaking this generates an autocovariance function, but an optionalnormalization (dividing each coefficient by the zeroth coefficient) producesthe autocorrelation function.

The program expects to read an AIM header, and interprets input as one largeframe in column-wise format (eg output from genbmm, gennap, etc.), to bedivided into input frames, each to be processed as an autocorrelogram.A new header is constructed, and each autocorrelogram frame is output inrow-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 fromthe 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 frstepoption is the frameshift between input frames in the input file.The special option value width=max specifies the input framewidth as equalto the given input file length, (and if this is also ’max’, then theinput 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 displayto pass straight through. Some options are set so that they can overridethe input header. For example, the display option is set on to enabledisplay even when input has display=off. The animate option can be set oneven 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 nextpower of 2 larger than either the original input framewidth or twice themax acf lag (whichever is the larger).If necessary, extra padding can be enforced using the (silent) padding optionto 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 isadded to double the size, and when n=2 the size is quadrupled, etc.).

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

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

The MRC makes no representations about the suitability of thissoftware for any purpose. It is provided "as is" without express orimplied warranty.

THE MRC DISCLAIMS ALL WARRANTIES WITH REGARD TO THIS SOFTWARE,INCLUDING ALL IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS, IN NOEVENT SHALL THE A.P.U. BE LIABLE FOR ANY SPECIAL, INDIRECT ORCONSEQUENTIAL DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM LOSS OFUSE, DATA OR PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE OROTHER TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE ORPERFORMANCE OF THIS SOFTWARE.