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Multiplexed signal files may be identified by examining the
fields of the array of
WFDB_Siginfo objects returned by
wfdbinit. Signals belonging to the same group
are multiplexed together in the same file. If all signals in a given signal
file have been sampled at the same frequency, and there are n signals
in the file, then each group of n successive samples in that file
contains a sample from each signal, always in the same order
(but see section Multi-Frequency Records).
Multiplexed signal files can be useful if the storage device is sequential-access only (e.g., 9-track tape), if the storage device has lengthy seek times (e.g., optical disk), if many signals must be recorded and Unix’s per-process limit on open files would otherwise be exceeded, or if very high speed is required while the file is being created (because of sampling constraints). CDROM signal files, and those available from PhysioNet, are multiplexed unless the record contains only one signal.
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