.TH CALSIG 1 "7 January 2009" "WFDB 10.4.12" "WFDB Applications Guide"
.SH NAME
calsig \- calibrate signals of a WFDB record
.SH SYNOPSIS
\fBcalsig -r\fR \fIrecord\fR [ \fIoptions\fR ... ]
.SH DESCRIPTION
.PP
\fBcalsig\fR (formerly known as \fBcalibrate\fR) rewrites the header file for a
WFDB record, setting the gain and baseline fields based on measurements it
makes, and setting the units fields based on input from the user or from a
calibration file. Normally, \fBcalsig\fR is used by specifying a time interval
for the measurements; best results will be achieved if the specified interval
is restricted to one or more square-wave calibration pulses in each signal to
be calibrated, although sine-wave pulses may be usable if the sampling
frequency and/or ADC resolution is high enough.
.PP
The program constructs a smoothed amplitude histogram for each signal and
identifies its two principal modes. Initially, each bin of the histogram
counts the number of samples in the analysis interval for which the amplitude
has a specified value. The histogram is smoothed by applying a low-pass filter
that replaces the contents of each bin by a weighted sum of fifteen bins
centered on the bin of interest. The two principal modes in the smoothed
histogram must be separated by at least one bin with a count that is less than
one-eighth the count of the larger mode. If this criterion is not satisfied
for a given signal, \fBcalsig\fR warns the user and does not adjust the gain
or baseline for the affected signal.
.PP
If a signal list is specified using the \fB-s\fR option (see below), only the
specified signals are calibrated, and the gain, baseline, and units fields for
any other signals are left unchanged. Thus, if calibration pulses are not
simultaneously available in all signals to be calibrated, \fBcalsig\fR may
be run repeatedly with different time intervals and signal lists.
.PP
.PP
\fIOptions\fR include:
.TP
\fB-c\fI file\fR
Obtain calibration pulse specifications from the specified \fIfile\fR (see
\fBwfdbcal\fR(5); default: obtain this information from the file specified by
the environment variable \fBWFDBCAL\fR, or interactively).
.TP
\fB-f\fI time\fR
Begin at the specified \fItime\fR in \fIrecord\fR (default: the beginning of
\fIrecord\fR).
.TP
\fB-h\fR
Print a usage summary.
.TP
\fB-q\fR
Instead of using the standard method for calibration, get a
`quick-and-dirty' estimate by taking the signal amplitudes at the
starting and ending times (as specified by \fB-f\fR and \fB-t\fR) as
representative of the low- and high-amplitude phases of the
calibration pulse. Use this option only if the standard method fails;
the standard method is more accurate.
.TP
\fB-Q\fR
Use an alternate `quick-and-dirty' estimate based on the range of signal
amplitudes over the interval specified by \fB-f\fR and \fB-t\fR. This
method may be easier to use than \fB-q\fR for signals with significant
high-frequency content, since it does not require precise location of signal
extrema. As noted above, the standard method is more accurate if it can be
used.
.TP
\fB-s\fR \fIsignal-list\fR
Calibrate only the signals named in the \fIsignal-list\fR (one or more input
signal numbers or names, separated by spaces; default: calibrate all signals).
.TP
\fB-t\fI time\fR
Process until the specified \fItime\fR in \fIrecord\fR (default: 1 second after
the starting time).
.TP
\fB-v\fR
Ask for calibration pulse limits (default: read limits from the calibration
file).
.SH ENVIRONMENT
.PP
It may be necessary to set and export the shell variables \fBWFDB\fR
and \fBWFDBCAL\fR (see \fBsetwfdb\fR(1)).
.PP
Calibration files must be located in one of the directories named in
\fBWFDB\fR, the database path. If the environment variable
\fBWFDBCAL\fR is set, it names a calibration file that will be read
unless the \fB-c\fR option is used to specify a different calibration
file. At most one calibration file is read; if more than one \fB-c\fR
option is given, only the last one is effective. If the calibration
file does not contain an entry for the type of signal to be
calibrated, \fBcalsig\fR obtains the information from the user
interactively. If the calibration file contains two or more entries
for the same signal type, only the first entry is used.
.SH SEE ALSO
\fBsetwfdb\fR(1), \fBwfdbcal\fR(5)
.SH AUTHOR
George B. Moody (george@mit.edu)
.SH SOURCE
http://www.physionet.org/physiotools/wfdb/app/calsig.c