tomwalters@0: .TH FFT 1 "15 September 1993"
tomwalters@0: 
tomwalters@0: .SH NAME
tomwalters@0: fft \- Fast Fourier transform of contiguous frames.
tomwalters@0: 
tomwalters@0: 
tomwalters@0: .SH SYNTAX 
tomwalters@0: fft  [arguments]  [file]
tomwalters@0: 
tomwalters@0: 
tomwalters@0: .SH DESCRIPTION
tomwalters@0: Several forms of fft processing are provided, according to the "spectrum"
tomwalters@0: option. Unless verbose output is requested, all input and output is in
tomwalters@0: binary shorts.
tomwalters@0: 
tomwalters@0: Each input frame is padded with zeroes to the next power of 2 larger than
tomwalters@0: the input framewidth.
tomwalters@0: If necessary, extra padding can be enforced using the (silent) padding option
tomwalters@0: to add extra zeroes, padding to a larger power of 2.
tomwalters@0: The amount of extra padding is "exponential", expanding the basic size to:
tomwalters@0: 
tomwalters@0:       ( framewidth + padding ) * 2**n
tomwalters@0: 
tomwalters@0: where the padding option is n.
tomwalters@0: 
tomwalters@0: (n=0 by default, so that no extra padding is added. When n=1 then padding is
tomwalters@0: added to double the size, and when n=2 the size is quadrupled, etc.).
tomwalters@0: The input and output frame sizes in sample points may be printed using the
tomwalters@0: "size" option.
tomwalters@0: 
tomwalters@0: 
tomwalters@0: .SH OPTIONS
tomwalters@0: 
tomwalters@0: The spectrum option selects a form of processing from the list:
tomwalters@0: 
tomwalters@0: 1. magnitude: magnitude spectrum
tomwalters@0: 
tomwalters@0: 2. log: log10 of magnitude spectrum
tomwalters@0: 
tomwalters@0: 3. phase: phase spectrum.
tomwalters@0: 
tomwalters@0: 4. complex: full complex spectrum, in <real,imag> pairs.
tomwalters@0: 
tomwalters@0: 5. inverse: inverse fft, reading framewidth numbers which are interpreted as
tomwalters@0: <real,imag> pairs, (ie framewidth/2 complex numbers),
tomwalters@0: and outputs the inverse transform scaled by 1/framewidth.
tomwalters@0: 
tomwalters@0: 6. verbose: prints the spectrum in ASCII on the stdout.
tomwalters@0: 
tomwalters@0: .SH EXAMPLES
tomwalters@0: .nf
tomwalters@0: 1. To print the input and output frame sizes in sample points,  
tomwalters@0:    eg for a subsequent plotting program, use the size option:
tomwalters@0: 
tomwalters@0: fft ... size=on
tomwalters@0: 
tomwalters@0: 
tomwalters@0: 2. An fft of a waveform sampled at 10kHz, computed within a 
tomwalters@0:    frame of 12.8ms, plotting the 2nd frame in a sequence of 
tomwalters@0:    frames with half-frame overlap.
tomwalters@0: 
tomwalters@0: fft samp=10kHz width=12.8ms frstep=6.4ms frame=2 file | x11plot
tomwalters@0: 
tomwalters@0: 
tomwalters@0: 3. An animated plot of successive fft spectra of a waveform 
tomwalters@0:    sampled at 10kHz, each computed within a frame of 12.8ms, 
tomwalters@0:    and shifted by 2 sample points.
tomwalters@0: 
tomwalters@0: fft samp=10kHz width=12.8ms frstep=2p file | x11play -n64
tomwalters@0: 
tomwalters@0: 
tomwalters@0: 4. Using the complex output from fft, and inverse transform 
tomwalters@0:    without windowing to recover original input.
tomwalters@0: 
tomwalters@0: fft samp=10kHz frame=2 spec=complex window=off file > foo
tomwalters@0: fft samp=10kHz frame=1 spec=inverse window=off foo | x11plot
tomwalters@0: 
tomwalters@0: .fi
tomwalters@0: 
tomwalters@0: .SH COPYRIGHT
tomwalters@0: .LP
tomwalters@0: Copyright (c) Applied Psychology Unit, Medical Research Council, 1995
tomwalters@0: .LP
tomwalters@0: Permission to use, copy, modify, and distribute this software without fee 
tomwalters@0: is hereby granted for research purposes, provided that this copyright 
tomwalters@0: notice appears in all copies and in all supporting documentation, and that 
tomwalters@0: the software is not redistributed for any fee (except for a nominal 
tomwalters@0: shipping charge). Anyone wanting to incorporate all or part of this 
tomwalters@0: software in a commercial product must obtain a license from the Medical 
tomwalters@0: Research Council.
tomwalters@0: .LP
tomwalters@0: The MRC makes no representations about the suitability of this 
tomwalters@0: software for any purpose.  It is provided "as is" without express or 
tomwalters@0: implied warranty.
tomwalters@0: .LP
tomwalters@0: THE MRC DISCLAIMS ALL WARRANTIES WITH REGARD TO THIS SOFTWARE, INCLUDING 
tomwalters@0: ALL IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS, IN NO EVENT SHALL 
tomwalters@0: THE A.P.U. BE LIABLE FOR ANY SPECIAL, INDIRECT OR CONSEQUENTIAL DAMAGES 
tomwalters@0: OR ANY DAMAGES WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, 
tomwalters@0: WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, 
tomwalters@0: ARISING OUT OF OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS 
tomwalters@0: SOFTWARE.
tomwalters@0: