Displaying and analysing bat calls using Cool Edit 2000 "Lite"

NB this is not a comprehensive guide to Cool Edit, but notes based on the (limited) experience of Lynn Whitfield and Ross Baker (Surrey Bat Group) using a Batbox Duet detector connected to a Sony MZ-R900 minidisc recorder.

Hardware/software notes

The minidisc should be connected to the pc using a lead with 3.5 mm stereo jacks at either end (two rings around the pins), plugged into the "line out" socket on the minidisc and the "line in" on the pc sound card. (Note: it is important to check that your sound card settings are correct - "line in" needs to be activated, usually by checking a box, and volume set above zero: try setting to maximum but you may need to fiddle with this.)

Downloading recordings to Cool Edit

  1. Open Cool Edit and click on File – New: a dialogue box will come up.
  2. Change settings to:

Sample rate: 44100

Channels: stereo

Resolution: 16-bit

And click on OK.

  1. On the above minidisc model, push in switch on left side to get "edit" menu, then press up or down to scroll to "audio out", and push in to select. Then toggle to "line out" and push in to select.
  2. Click on the Cool Edit record button (red spot, bottom left panel).
  3. Start playing back the recording from the minidisc (on above model, toggle switch on right hand side to required track, and push in to play). You should hear the minidisc playing back through the pc.
  4. Stop the playback after the required amount of time and stop the Cool Edit recording by clicking on the grey square in the bottom left panel. (NB These sound files take up huge amounts of hard disk space, and if they get too big can make the program crash, so best not to save too much at a time, or save files after analysis - just save the interesting bits. If you're having problems you can increase the allocation of temporary file space by clicking on Options - Settings - System tab and increasing the number in the Temp directory box.)

Frequency analysis

  1. Click on the main screen, which should produce a green waveform on a black background ("waveform view"). (NB The upper screen shows the frequency division readout, which is the one you want; the lower one is the heterodyne signal - ignore this.) Put the cursor (white arrow plus L shape) on the left of the section you want to analyse, hold down the left mouse button, move across to the right of the section and release.
  2. Click on "zoom to selection" (panel 2, bottom left – button with magnifying glass in open square). Repeat this procedure (select and zoom) until individual bat "clicks" are expanded enough to be able to see the shape of the waveform clearly: check this by going to "spectral view" (see 3 below). (Note: other buttons in this panel allow you to zoom in and out in various ways: we have not detailed them all here. Always zoom in and out in waveform view - takes ages in spectral view.)
  3. Go to "spectral view" (either via the View menu in the toolbar, or using the toggle switch - the one with the diagonal line across it - further along the toolbar). This should produce a red and yellow waveform on a blue background.
  4. The yellow colour represents the highest-intensity parts of the sound. Place the cursor (vertical line) so that it goes through the most solid yellow area of the call, then click on "Analyse" in the toolbar, then on "Frequency analysis". An inset screen will come up, with a graph of sound intensity vs frequency, ie it is showing the intensity of all the different frequencies being emitted at the part of the call selected. Ensure the two left hand boxes along the bottom are set at "1024" and "Hanning". The peak echolocation frequency is given in the box above these, eg:

Frequency L = 3942.4 Hz

This number has to be divided by 100 (move decimal point two places left!) to get the frequency as it is normally expressed, in kiloHertz (kHz) (because 1 kHz = 1000 Hz, and the graph is displaying the frequencies divided by 10). So the above reading will be 39.4 kHz.

  1. The above reading will probably be correct when there is a single definite peak on the frequency graph, but if there is more than one similar-sized peak, or an indistinct peak (eg the plateau-like graph usually produced by Myotis bat calls) it may not be. Check by placing the cursor on where you think the main peak is: this will produce an alternative reading from any part of the graph.

Interpulse interval analysis

  1. Close the frequency analysis window and toggle back to waveform view (see above).
  2. Select a section of the screen that contains at least five or six reasonably evenly-spaced calls by dragging the cursor across as before, with the start and end of the section at the same position within the call. The time in milliseconds (ms) covered by the selection is displayed at the bottom right of the screen, under "length": divide this by the number of intervals between calls to get the interpulse interval.

Saving selected calls

  1. Highlight the section you want to save using the cursor as above.
  2. Click on File - Save selection as - and change the file type to "Microsoft ADPCM (*.wav)" before saving it under an appropriate name/directory. (Some of the other file types don't seem to work.)
  3. Close the file before playing in the next section.

 

RDB/LW

24.3.03