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来自「speech signal process tools」· DIFF 代码 · 共 255 行

.\" Copyright (c) 1990 Entropic Speech, Inc. All rights reserved.
.\" @(#)fft_filter.1	3.10	9/25/98 ESI
.TH FFT_FILTER 1\-ESPS 9/25/98
.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_filter \- Performs FIR digital filtering on a sampled data file using
frequency domain convolution instead of time domain convolution.
.SH SYNOPSIS
.B fft_filter
[
.BI \-P " param_file"
]
[
.BI \-x " debug_level"
]
[
.BI \-f " filtername"
]
[
.BI \-F " filt_file"
]
[
.BI \-p " range"
]
[
.BI \-r " range"
]
[
.B \-z 
]
.I in_file out_file
.SH DESCRIPTION
.PP
The program
.I fft_filter
takes the input sampled data file,
.I in_file,
and produces an output sampled data file,
.I out_file,
after performing a finite impulse response (FIR) 
digital filtering operation on it.
The program accepts "\-" for either the input file or the output file
to use the standard input and standard output, respectively. 
This program accomplishes the filtering operation by multiplying in the
frequency domain, instead of convolving in the time domain.  
If the filter length is large (i.e.
> 50 taps), 
this has
the effect of greatly reducing the number of computations required
to perform the filtering operation.
.PP
The program performs only FIR filtering.
A set of numerator coefficients are specified 
either in a parameter file or in a FEA_FILT(5\-ESPS) file.
The numerator coefficients then become the {a\di\u}
in the following
z-domain transfer function:
.nf

        
 		H(z) = a\d0\u + a\d1\uz\u-1\d + a\d2\uz\u-2\d + ... + a\dm-1\uz\u-m+1\d


.fi
The first output sample will be computed from data samples
occurring before the starting point in the input file (as defined by the parameter
.I start
, for example), if they exist.  Data samples which would occur before
the first sample in the input file are assumed to be zero.
.sp
.SH OPTIONS
The following options are supported:
.TP
.BI \-P " param_file"
uses the parameter file 
.I param_fil
rather than the default, which is
.I params.
.br
.TP
.BI \-f " filtername"
If the coefficients are being read from the parameter file, then
.I filtername
is the body of the name in the params file
that contains both the number of coefficients and the actual coefficients.
This means that the coefficients will be
found in the array
.I filtername_num,
and the size of that array will be specified by
.I filtername_nsiz.
The default name for the body of these parameter file entries is
.I filter.
.IP
If the coefficients are being read from a FEA_FILT file, then
.I filtername
is the number of the fft_filter record to use.
The default name in this case is 1, the first record in the file.
.br
.TP
.BI \-F " filt_file"
Read the coefficients from the FEA_FILT file
.I filt_file
rather than from the parameter file.
In this case the header of 
.I filt_file
is added to the header of the program output as a source file.
If the denominator size is neither zero nor one an error 
message will be printed and \fIfft_filter\fR will exit.
.br
.TP
.BI \-x " debug_level"
A value of zero (the default value) will cause
.I fft_filter
to do its work silently, unless there is an error.
A nonzero value will cause various parameters to be printed out
during program initialization.
.br
.TP
.BI \-p " range"
Perform the filtering operation on the specified range of points.
.I range
is a character string which is interpreted by
\fIrange_switch\fP(3-ESPSu).
\fBp\fP and \fBr\fP are synonyms.
.br
.TP
.BI \-r " range"
Perform the filtering operation on the specified range of points.
.I range
is a character string which is interpreted by
\fIrange_switch\fP(3-ESPSu).
\fBp\fP and \fBr\fP are synonyms.
.TP
.BI \-z
If specified,
the \fIstart_time\fP generic value is reduced by the value of the
\fIdelay_samples\fP generic header value, if it exists. This often
helps time align a filtered
signal with the input signal. 
Note that
if \fIdelay_samples\fP is not defined in the input file header,
a value of 0 is assumed.
.SH ESPS PARAMETERS
.PP
The values of parameters obtained from the parameter file are printed
if the environment variable ESPS_VERBOSE is 3 or greater.  The default
value is 3.
.PP
Where command line options conflict with
parameter file options, the command line values are used.
The following parameters are read from the parameter file.
.IP
.I "start \- integer"
.IP
The first point in the input sampled data file that is processed.
The samples are assumed to be numbered starting with one so that
setting 
.I "start = 1"
will cause processing to begin with the first sample.
.sp
.I "nan \- integer"
.IP
The number of points in the sampled data file to process.
.sp
.I "filtername_nsiz \- integer"
.IP
The number of coefficients in the transfer function for the filter
.sp
.I "filtername_num \- float array"
.IP
The numerator coefficients.  They are specified in order starting with
a\d0\u.
.sp
.SH ESPS COMMON
If the input
is standard input, COMMON is not read. If COMMON is read and the 
command line input filename does not match the filename listed in COMMON,
no further parameters are read from COMMON. Finally,
if the two filenames match,
the following items are read. 
.IP
.I "start - integer"
.IP
This is the starting point in the input file. Any \fB\-p\fR
option value supersedes the COMMON specified value.
.IP
.I "nan - integer"
.IP
This is the number of points to analyze. A \fB\-p\fR specified value
supersedes the COMMON specified value.
.PP
If the output is standard output,
COMMON is not written.
Otherwise the following items are written to COMMON.
.IP
.I "filename \- string"
.IP
This is the name of the output file.
.IP
.I "start \- integer"
.IP
This is the starting point in the output file
and is always equal to one.
.IP
.I "nan \- integer"
.IP
This is the number of points in the output file.
.PP
ESPS Common processing may be disabled by setting the environment variable
USE_ESPS_COMMON to "off".  The default ESPS Common file is .espscom 
in the user's home directory.  This may be overidden by setting
the environment variable ESPSCOM to the desired path.  User feedback of
Common processing is determined by the environment variable ESPS_VERBOSE,
with 0 causing no feedback and increasing levels causing increasingly
detailed feedback.  If ESPS_VERBOSE is not defined, a default value of 3 is
assumed.
.SH ESPS HEADER
The file header of
.I out_file
will contain much of the same information as is contained in 
.I in_file,
except where they are altered by the parameters in the parameter file.
The filter coefficients will be stored in the output header as the
.I fft_filter
zfunc.
.PP
A generic header item \fIstart_time\fR (type DOUBLE), is added
to the output file header. It contains the starting time in seconds of the
first point in the output file. This start time is relative to the original
sampled data file. This means that if the input file has a \fIstart_time\fR
generic in it, the output file's \fIstart_time\fR value is computed
relative to the input file's \fIstart_time\fR. Also see the \fB\-z\fP
option.
.PP
For example, if the input file has a \fIstart_time\fR = 1.0 seconds,
the input file's sampling frequency = 8000 samples/second, and the 
starting point in the input file = 2000, the output file's 
\fIstart_time\fR = 1.0 + 2000/8000 = 1.25 seconds. 
.SH FUTURE CHANGES
.PP
.SH SEE ALSO
.PP
.nf
\fIFEA_FILT\fP(5-ESPS), \fIfilter\fP(1-ESPS), \fIwmse_filt\fP(1-\ESPS),
\fIatofilt\fP(1\-ESPS), \fiFEA_SD\fP(5-ESPS), \fIiir_filt\fP(1-ESPS),
\fIsfconvert\fP(1-ESPS)
.fi
.sh BUGS
.PP
None known.
.SH AUTHOR
.PP
Brian Sublett; ESPS 3.0 modifications by David Burton; FEA_FILT modifications
by Bill Byrne