- High-pass and low-pass filters
- Full spectrum High Pass filters
- Frequency division high pass filters
As indicated in the user manual when the full spectrum high pass filter is turned on, certain audible sounds will not be recorded, such as those produced at frequencies below 15 kilohertz. Things like conversations, walking on dry grass and / or leaves, and other undesirable sounds.
Use of this filter is recommended during recording attempts in strong winds, or when one is in fact walking on dry leaves, dry grass, etc.
With the full spectrum high pass filter enabled, the lower-frequency limit of recorded signals will be approximately 150 Hertz, which enables things like verbal comments, other voices, and other normally audible sounds.
During my Summer of testing, I rarely came across a situation in which I needed to enable it. When using even the default settings, there weren't many instances where sounds other than bats triggered the LunaBat. I would just hit 'OK' to record, and walk...
If you have dry leaves underfoot during your survey, bat-walk, etc., then in addition to the filter, you can adjust the trigger level. Regardless of the mode I used, no background hiss was heard from this detector.
All of this is covered in more detail in part 3.9 (page 15) of the user manual.