fft.1

speech signal process tools

.\" @(#)fft.1	1.2 6/18/87
.\" Copyright (c) 1987 Entropic Speech, Inc.; all rights reserved
.TH FFT 1\-ESPS 6/18/87
.ds ]W "\fI\s+4\ze\h'0.05'e\s-4\v'-0.4m'\fP\(*p\v'0.4m'\ Entropic Speech, Inc.
.SH "NAME"
fft \- Fast Fourier Transform of ESPS SD file to an ESPS SPEC file
.SH "SYNOPSIS"
.B fft
[
.BI \-p " range"
] [
.BI \-o " order"
] [
.BI \-r " nframes"
]
.I sdfile
.I specfile
.SH "DESCRIPTION"
.PP
.I Fft
takes an input ESPS Sampled Data file, 
.I sdfile,
and takes the Fast Fourier Transform of one or more fixed-length 
segments to produce an ESPS Spectral Record file
.I specfile
containing one or more spectral records.  
.sp
If the input file name
.I sdfile
is replaced by "-", then stdin is read; similarily, if
.I specfile
is replaced by "-", then the output is written to stdout.
.PP
.SH "OPTIONS"
.PP
The following options are supported:
.TP
.BI \-p " range"
Selects a subrange of points from 
.I sdfile
using the format 
.I start\-end,
.IR start:end,
or
.IR start:+delta .
Either 
.I start
or 
.I end
may be omitted, in which case the omitted parameter defaults respectively
to the start or end of 
.I sdfile
The first recored in 
.I sdfile
is considered to be point 1, regardless of its position relative to any
original source file.  The form 
.I start:+delta
is equivalent to 
.I start:(start+delta).  
If the \fB\-p\fP option is not used the
range is determined from the ESPS Common file if the appropriate
parameters are present (see ESPS COMMON).  Otherwise the default
range is the entire input file
.I sdfile. 
.TP
.BI \-o " order\fR[10]\fP"
The order of the fft.  If the number of data points in each frame is
less than 2^order (2 to the order-th power), the frame is padded with
zeros.  If the number of data points in each frame exceeds 2^order,
only the first 2^order are used.  The number of frequencies in the
output spectral records is 1 + 2^(order - 1).  The default order is
10 and the largest possible order is 14.
.TP
.BI \-n " nframes\fR[1]\fP"
The number of fixed-length frames processed.  The frame length is 
determined by the 
.I range
from the \fB\-p\fP option or from the ESPS Common file.  (See the 
discussion under the \fB\-p\fP option and in the section ESPS
COMMON).  
.SH "ESPS PARAMETERS"
.PP
The parameter file is not read.  
.SH "ESPS COMMON"
.PP
It the \fB\-p\fP option is not used, the parameters 
.I start
(starting point) and 
.I nan
(number of points) are read from ESPS Common if they exist and 
if the Common parameter
.I filename 
matches
.I sdfile. 
If 
.I specfile
is not standard output, the Common parameters 
.I "filename, prog, start,"
and
.I nan
are written to correspond to the first selected range in the 
input file 
.I sdfile. 
.SH ESPS HEADERS
.PP
.I fft
reads the value of 
.I common.type
from the input SD file 
.I sdfile.  
.PP
Relevant fields in the type-dependent portion of the 
output file header are filled appropriately.  
The generic header item 
.I "fft_length"
is set to the length of the fft (2^order).  
.SH "FUTURE CHANGES"
.PP
.SH "SEE ALSO"
.PP
get_fft (3-ESPS), refco (1-ESPS), anaspec (1-ESPS), SD(5-ESPS),
SPEC(5-ESPS), ESPS(5-ESPS).
.SH "BUGS"
.PP
.SH "REFERENCES"
.PP
J. W. Cooley and J. W. Tukey, "An Algorithm for the Machine Calculation of
Complex Fourier Series," \fIMath. Computation\fP, Vol. 19, 1965, pp. 297-301.
.sp
Alan V. Oppenheim and Ronald W. Schafer, \fIDigital Signal Processing\fP.
Englewood Cliffs, New Jersey: Prentice-Hall, Inc., 1975.
.SH "AUTHOR"
.PP
manual page and program by Rod Johnson; revised by John Shore