Keywords: wfdb_tools

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# Sample, signal, and annotator numbers

Several WFDB library functions, and most of the stand-alone WFDB applications, accept arguments that specify a specific sample within a digitized signal (a sample number, a specific signal within a set of signals (a signal number, or a specific set of annotations (an annotator number). The first sample number in a signal has sample number 0, not 1; similarly, the first signal has signal number 0, and the first annotator has annotator number 0. The WFDB_tools functions use the same zero-based sample, signal, and annotator numbers as the WFDB library functions that they wrap. This point is a possible source of confusion if you become accustomed to thinking of these numbers as array indices (which, in C, is exactly what they are); it may be best to think of them simply as identification numbers for the objects with which they are associated.