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Signal Processing Applications

rdsamp -r record [ options ... ]
wrsamp -r record [ options ... ]
snip -i input-record -n new-record [ options ... ]
xform -i input-record [ options ... ]
fir [ options ... ] -c coefficient ...
sigamp -r record [ options ...]
sqrs -r record [ options ... ]
sample [ options ... ]
calsig -r record [ options ... ]

rdsamp’ prints samples from the specified record; ‘-f’ and ‘-t’ options may be used to specify a range of sample numbers, and a subset of signal numbers may be selected using the ‘-s’ option. The output of ‘rdsamp’, or any similar text, can be converted into a WFDB record using ‘wrsamp’.

To copy an excerpt of a longer record, use ‘snip’, which creates new header and signal files for new-record in the current directory. The beginning and end of the excerpt are specified using ‘-f’ and ‘-t’ options as for ‘rdsamp’. Annotator names may follow a ‘-a’ option; in this case excerpts from the specified annotation files are copied as well (the annotations are appropriately time-shifted).

xform’ is a more general version of ‘snip’; its main uses are for reformatting, rescaling, and sampling rate conversion. You may create a ‘hea’ file specifying the desired format, sampling frequency, ADC zero levels, signal gains, etc., and supply it to ‘xform’ using the ‘-o’ option; if you do not do so, ‘xform’ obtains the required information interactively. ‘xform’ accepts all of the options used by ‘snip’, as well as several others.

Program ‘fir’ is a general-purpose FIR filter for WFDB records, similar to the one discussed in chapter 6 (see section Example 7: A General-Purpose FIR Filter).

sigamp’ measures signal amplitudes (either baseline-corrected RMS amplitudes or peak-to-peak amplitudes); it may be useful for calibrating signals (together with ‘calsig’) or for determining signal gains for ‘nst’.

sqrs’ is a slightly modified version of the QRS detector discussed in chapter 6 (see section Example 10: A QRS Detector). Options allow specification of the signal and interval to be analyzed and the detection threshold.

Program ‘sample’ is an MS-DOS application that uses a Microstar Laboratories DAP 1200- or 2400-series ISA (AT bus) analog interface board (see section Sources) to generate database records from analog signals, or to generate analog signals from database records. If you wish to use other hardware for these purposes, refer to chapter 6 (see section Example 8: Creating a New Database Record) and to the source for ‘sample’ as models.

If you create your own database records using ‘sample’ or other means, program ‘calsig’ may be useful for determining signal gains and offsets if your signals include standard calibration pulses or identifiable signal levels. ‘calsig’ incorporates two independent algorithms for measuring calibration pulses; it rewrites header files based on its measurements.

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George B. Moody (george@mit.edu)