The ultrasonic microphone built into the Song Meter Mini Bat (generations 1 and 2) has a permanent high-pass filter (HPF) with a cutoff frequency of 8.25 kHz. An HPF is a filter designed to remove incoming signals below its cutoff frequency. In the case of the Song Meter Mini Bat, the purpose of the HPF is to prevent low-frequency sounds like wind from distorting your recordings or excessively triggering the recorder.

Most filters take effect gradually as frequency changes. In the case of the Song Meter Mini Bat, for each factor of 2 below the cutoff frequency, sound at that frequency is reduced in volume by 12 dB compared to sound above the cutoff frequency. For example, sound at 4.13 kHz is reduced by 12 dB, and sound at 2.06 kHz is reduced by 24 dB.

You should only expect to record sound as low as approximately 8 kHz, but you may still see slightly lower-frequency sounds recorded if they are particularly loud.

If want to consistently record lower-frequency sound, you should install an acoustic stub microphone on your Song Meter Mini Bat and schedule the recorder for acoustic recording.

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