Glossary
This glossary defines key terms used throughout the WFDB specification, software, and associated documentation.
WFDB (Waveform Database)
A general term that refers to a set of open standards, file formats, and software for representing, storing, and analyzing physiologic waveform and annotation data. Originally developed at MIT by George B. Moody in 1989.
WFDB Specification
The formal definition of the WFDB file formats: headers (.hea), signal files (.dat), and annotation files (.atr, .ann, etc.).
The specification describes how physiologic data and event annotations should be encoded, independent of any software implementation.
WFDB Software
The collection of software tools, libraries, and applications that read, write, visualize, and process WFDB-formatted data.
This includes the original WFDB C library, Python packages, MATLAB toolboxes, and command-line utilities.
AC-coupled Signal
A signal (e.g., ECG) for which only variations in level are significant. Baseline (DC offset) is removed prior to digitization.
ADC (Analog-to-Digital Converter)
A device that converts continuous analog signals into discrete digital samples.
ADC Resolution
The number of significant bits per sample produced by the ADC, determining the granularity of the digital representation.
ADC Zero
The digital output value corresponding to a 0-volt input. For unipolar ADCs, this is typically 1024.
ADU (Analog-to-Digital Unit)
The native unit of a digital sample before conversion to physical units. Values are in integers corresponding to ADC output.
AHA Format
A legacy annotation format originating from the American Heart Association (AHA) database standard.
It uses fixed-length annotation records (16 bytes each).
Annotation
A marker associated with a specific sample, identifying events like heartbeats, arrhythmias, or comments.
Annotation File
A binary file (e.g., .atr, .ann) containing annotations linked to a signal record.
Base Counter Value
A value corresponding to the counter (e.g., tape counter) at sample 0, used for mapping counter ticks to time.
Base Date
The date at which the record begins, specified in DD/MM/YYYY format.
Base Time
The time of day when the recording starts, in HH:MM:SS format (24-hour clock).
Channel
A single data stream within a record, such as an ECG lead or arterial blood pressure waveform. Typically a record will include multiple channels.
Counter Frequency
The number of counter ticks per second, used for records originally stored on analog media.
Digital Signal
A signal after analog-to-digital conversion, consisting of discrete numerical samples.
Frame
A set of simultaneous samples from all signals at a single time point.
Gain
A scaling factor to convert from ADUs (digital units) to physical measurement units like millivolts or mmHg.
Header File
A text file (.hea) that defines the metadata for a WFDB record, including signal specifications.
Multi-segment Record
A record composed of multiple segments, allowing variable signal types or gaps in recording.
Physical Signal
The reconstructed analog signal after scaling the digital samples by gain and baseline correction.
Record
A named collection of files (header, signal, annotation) representing a single physiologic recording.
Record Line
The first non-comment line of a header file, summarizing basic properties like number of signals and sampling rate.
Sampling Frequency (fs)
The number of samples acquired per second, specified in Hertz (Hz).
Signal File
A binary file (e.g., .dat) containing waveform samples for one or more channels.
Signal Specification Line
A line in the header file that describes a specific signal’s properties, including format, gain, units, and file name.
Units
The physical measurement units (e.g., millivolts, mmHg) associated with a signal, specified in the header file.
This glossary is intended to serve as a quick reference when working with WFDB-formatted data.
For full technical specifications, please refer to the WFDB Programmer’s Guide and WFDB Applications Guide.