fir - general-purpose FIR filter for WFDB records
fir [ options
... ] -c [ coefficients ... ]
fir can be used to apply any desired
finite impulse response filter to any desired section of a waveform database
record. Options are:
- -c coefficient [ coefficient ... ]
- Filter using the specified
coefficients (must be the last option; -c marks the beginning of the coefficient
- -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).
- Print a
- Read the signal files in high-resolution mode (default:
standard mode). These modes are identical for ordinary records. For multifrequency
records, the standard decimation of oversampled signals to the frame rate
is suppressed in high-resolution mode (rather, all other signals are resampled
at the highest sampling frequency).
- -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).
- Rectify the input (i.e., take its absolute value)
- 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.
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.
It may be
necessary to set and export the shell variable WFDB (see setwfdb(1)
low-pass "boxcar" filter:
fir -c .2 .2 .2 .2 .2
The complementary high-pass filter:
fir -c -.2 -.2 .8 -.2 -.2
fir -c .4
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
George B. Moody (firstname.lastname@example.org)
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Updated 26 January 2018