Guide to filters and scans

Anabat Training’s Anabat Level 2 and Level 3 courses provide training in these two functions of the Analook program.  Check our course dates for the next course.

Filters can be selected from the menu bar. They enable the user to:

  • Set a filter, restricting search of data to that within selected parameters
  • Search for bats in a particular frequency band
  • Apply species specific filters
  • Apply filters to remove noise that is not made by bats

How to create a filter

While in the Analook folder that you want to apply a filter to:

  • Select Filter –> New Filter, from the top menu bar

Screenshot of filter use

Select 'Filter' from top menu

  • Select ‘Body’ tab
  • Insert appropriate parameters in one or more of the boxes (e.g. Fc, Sc, Dc etc)
Screenshot of filter use

Insert appropriate parameters in one or more of the boxes

  • Tick ‘Use’ box for each of your parameters
  • Select ‘Apply and Close’
  • Give the filter a name e.g. ‘barbfilter’
  • Put under a folder called ‘Filters’ in the Analook folders
  • Save
  • Reopen ‘Filters’ from the top menu bar
  • Select ‘Load’
  • Choose the filter you want – this will then be applied to your Analook folder.  All sound files will then only show sonograms that conform to the species filter applied.  This filter can be edited, by selecting ‘edit’ while the filter is applied (see below)

Creating an all bats filter or anti-noise filter (so anything other than bat sounds are removed)

  1. Select Filter
  2. Select New Filter
  3. Select ‘Calls’ Smoothness to 50
  4. Select ‘Body’ Body Over to 1000
  5. Fc min 15 and max 120. Check Use
  6. Select ‘Times’ Dur min 2 and max 100. Check Use.
  7. Select ‘Apply and Close’
  8. Check to see what you have filtered out by selecting off dots. Then edit the filter until you are happy with the results

Editing Filters

  1. Load ‘All bats’ filter
  2. Select Edit
  3. Choose new parameters from tabs and watch to see how this affects the files
  4. What do you lose or gain?
  5. Further refine the filter until you are satisfied with it

Quote from Chris Corben on Filters

The use of filters is a step towards automated identification of bat calls. Some species will be easy, but many will prove difficult to distinguish from others. The use of filters is based on the concept that most species will produce some calls that are diagnostic of that species in a given locality.

But it also assumes a comprehensive knowledge of identification criteria.

Scans

  • Scans enable you to run filters on large amounts of data – from whole folders or folder ‘trees’
  • Enable you to run multiple filters on same data with one scan
  • Several filters run together can target different call types of the same species (e.g the two-part call of a Barbastelle)
  • They allow you to summarise results of pulses which passed filters
  • You can also measure sonogram parameters of all pulses that passed filter
  • Output is in a text file which can be imported to Excel and statistically analysed

Conclusions of Filter & Scan usage

  • Enables objective, consistent and repeatable analysis results
  • Enables scanning of large data sets which is often essential in research work
  • But, there are limitations! A filter is only as good as the parameters you put into it!
  • To be successful with Filters & Scans
    • Understand their limitations
    • Tailor the Filter to your needs

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