Manual Reference Pages - ACGRAM (1)
acgram - Autocorrelogram auditory image.
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. 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.).
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 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.
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|SunOS 5.6||ACGRAM (1)||1 September 1993|