Multiplexed signal files may be identified by examining the group
fields of the array of DB_Siginfo objects returned by
isigopen or dbinit. 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). CD-ROM signal files are multiplexed unless the record contains only one signal.
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