1.4. Manipulating EDF record size

As previously noted, M06 had an unusual (and large) EDF record size (17s). Although it is perfectly valid to have an EDF record size of 17s per se, it can make working with EDFs harder, e.g. if wanting to distribute variant forms of the file, e.g. restricted to sleep intervals only, etc. This is because an EDF record is the atomic unit of the EDF - a whole record is either included or excluded, partial records are not allowed.

Also, with many signals and/or high sampling rates, a large EDF record duration may lead to an EDF record size (in bytes) larger than the EDF specification allows: although Luna is permissive in this regard, other tools may not be able to open an EDF with excessively large record sizes, and so it can be useful to alter this.

Changing record size

There is an easy fix: we can use the RECORD-SIZE command to alter it, here to enforce 1-second records. The command below also writes a new EDF (M06-v2.edf) with this altered record size:

luna s1.lst id=M06 -s RECORD-SIZE dur=1 edf-dir=work/data/edfs/ edf=M06-v2

You can test this worked, e.g. here with the SUMMARY command:

luna work/data/edfs/M06-v2.edf -s SUMMARY

EDF filename   : work/data/edfs/M06-v2.edf
Patient ID     : M06                                                                             
Recording info : .                                                                               
Start date     : 01.01.85
Start time     : 22.00.00

# signals      : 59
# records      : 27404
Rec. dur. (s)  : 1
...

In practice, we may want to confirm that the new file is valid a little more, or at least to keep a backup of the original. But here, we'll directly swap this file back in, overwriting the 17s M06.edf:

mv work/data/edfs/M06-v2.edf work/data/edfs/M06.edf

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Having taken care of this one (potential) issue, we can now turn to reviewing the channels present across the EDFs.