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Avisoft-SASLab Pro Tutorial
Some sound files are difficult to analyse because of
long silent sections between the single vocalizations you are
interested in. Examples are sporadically emitted contact calls in
birds or bat echolocation calls.
Figure 1: The
uncompressed total display of the original file provides poor
information on the single calls because of large inter-call
durations.Avisoft-SASLab provides a feature for simplifying the
analysis of such signals. The breaks between the calls can be
removed either manually or automatically. The information about
removed parts of the file is saved in the .wav file header enabling
precise temporal measurements between the compressed elements and
even subsequent re-construction for visual inspection of the
original time structure.
Figure 2: The
compressed display provides much more information on the single
calls, while the inter-call duration can still be measured by
cursors (the call interval between the first two calls measured from
the marker cursor is 39 msec).Manual compressionManual compression
is done by first generating section labels. Press the <Shift>
key and click at the start of the first element and drag the label
to the end of that element. Repeat this procedure for each
element:
Figure 3:
Inputting section labels by pressing the shift key and mouse click
and dragThese section labels can be removed or resized until they
cover all the signals you want to keep for analysis. Then execute
the command Edit/Compress/’Remove gaps between section labels’. The
cutting locations are indicated by vertical marks at the top of the
waveform display (see Figure 2). Measuring cursors in both the main
and spectrogram window and the Automatic Parameter Measurement take
this compression into account and will display the original time
values.Use the option Edit/Compress/’Expanded view’ to toggle
between compressed and expanded view. Both this option state and the
original time structure information is saved into the .wav file
header. Use the command Edit/Compress/’Delete time compressing
information from file’ to remove that additional information from
the sound file.
Automatic compression.
The
compression described above can be automated by using the
spectrogram window command Tools/Automatic parameter
measurements/’Remove gaps between detected elements.’ Do not
activate the option ‘Insert break marks, because this would probably
inconvenient for subsequent analysis. Before executing this command,
appropriate parameters for the Automatic Parameter Measurements must
have been chosen. For details on set up see also Measuring
sound parameters from the spectrogram
automatically. | |
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