ECG Database Applications Guide
Table of Contents
fir - general-purpose FIR filter for DB records
fir [ options
... ] -c [ coefficients ... ]
fir can be used to apply any desired
finite impulse response filter to any desired section of a database record.
Options are:
- -c coefficient [ coefficient ... ]
- Filter using the specified
coefficients (must be the last option; -c marks the beginning of the coefficient
list).
- -C file
- Read the filter coefficients from the specified file rather
than from the argument list.
- -f time
- Filter from the specified time on the
input record (default: start at the beginning of the record).
- -h
- Print a
usage summary.
- -i record
- Use the specified record for input (default: record
16).
- -n record
- Create a header file for the output signals, with the specified
record name. The signal descriptions are copied from those of the input
signals.
- -o record
- Use the specified record for output (default: record
16).
- -ri
- Rectify the input (i.e., take its absolute value) before filtering.
- -ro
- Rectify the filtered output.
- -s shift
- To compensate for phase shift,
read ahead on the input record by the specified interval before starting
the filter. Shift is specified in standard time format (use snn to compensate
for a phase shift of nn samples).
- -t time
- Filter until the specified time
on the input record (default: go to the end of the record).
Unless the
-C option is used, the -c argument should appear at the end of the option
list. Filter coefficients are real numbers separated by spaces; the last
coefficient is applied to the most recent input sample.
In the present
implementation, the same filter is applied to each input signal. If the
output record header file specifies fewer signals than are present in
the input, any extra input signals are discarded.
The shell variable DB
should be set and exported (see setdb(1)
).
A low-pass "boxcar" filter:
fir -c .2 .2 .2 .2 .2
The complementary high-pass filter:
fir -c -.2 -.2 .8 -.2 -.2
An
attenuator:
fir -c .4
A differentiator:
fir -c -1 1
A 60-Hz notch filter, with
partial correction for phase shift, for the MIT-BIH database (360 samples/second):
fir -s s2 -c .5 0 0 .5
A "triangle" filter for QRS detection (at 128 samples/second):
fir -s s8 -c -1 -2 -3 -4 -1 2 5 8 5 2 -1 -4 -3 -2 -1
mfilt(1)
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