snippet sound data is compressed using the lossless X3 compressor but this is transparent to
the user: the .dwv file contains the reconstituted uncompressed data. Up to 100000 snippets
will be saved per recording (i.e., per output file). If more detections are made over this
interval, they will be reported in the BCL file (see below) but no snippet will be saved. This
puts an upper limit on the memory usage rate making it easier to calculate for how long the
SoundTrap will be able to record.
•
bcl
This is a comma-separated-variable (CSV) text file containing information about
detections. Each line has 7 columns with the following format:
Seconds (in Unix seconds), Microseconds, Report type, Info1,Info2,Info3,Info4,
To obtain high enough resolution, timing information is spread over two fields (Seconds and
Microseconds). The time of each entry is then Microseconds/1e6. The four Info
fields are determined by the report type of which there are two. Detections have a report
type of 'D'. The next two fields (Info1 and Info2) indicate whether a snippet was saved (1 or
0) and the noise level at the time of the detection. Fields Info3 and Info4 are not used in
detection reports. The second report type is an effort report which has a type of 'E'. The
effort report indicates the times over which the detector was operating. There will usually
be an on-effort report at the start of each recording (i.e., with a detector state of 1) and an
off-effort report at the end of each recording. The on-effort report has no other data and so
appears as:
seconds,microseconds,E,1,,,
The off-effort report appears as:
seconds,microseconds,E,0,noise level,ndets,nsaved,
where ndets is the total number of detections made since going on effort and nsaved is the
number of these for which snippets were saved. In both report types, the noise level is given
in Centibels, i.e., 100 log10(p) where p is the noise power referenced to the recorder
calibration. The absolute threshold used for each detection is then p+10^(RDT/10). If no
detections were made throughout a recording, the BCL file will contain two lines:
start_time,microseconds,E,1,,,
end_time,microseconds,E,0,noise level,0,0
If there are detections, they will be bracketed between these lines and the appropriate
detections counts will be changed in the off-effort report. The BCL file can be read and
