Recording quality and bat detection differences between the Song Meter Mini Bat 2 and SM4BAT FS

The Song Meter Mini Bat 2 uses the same microphone element as the SMM-U2 cabled ultrasonic microphone, so the audio quality of the Mini Bat 2 is very similar to the quality of a Song Meter SM4BAT FS paired with an SMM-U2 microphone.

The Mini Bat 2 and the SM4BAT FS use automatic trigger mechanisms to detect and record nearby bats, and these mechanisms have different levels of sophistication.

Bat detection in the Song Meter Mini Bat 2

The Mini Bat 2 uses a trigger mechanism we call broadband triggering. When active, the recorder monitors the level of incoming sound to gauge the average level of ambient background noise above its built-in high-pass filter. When it detects a bat call that peaks above the background noise by a certain amount, the Mini Bat 2 starts recording until the bat has flown away.

We call this broadband triggering because the Mini Bat 2 measures the level of all sound as a single, broad band. It doesn't matter whether the incoming sound is at 20 kHz or 80 kHz; it just has to be louder than the overall level of background noise.

Bat detection in the Song Meter SM4BAT FS

The SM4BAT FS uses a more complex mechanism we call narrowband triggering. Rather than measuring all incoming sound as a single, broad band, the SM4BAT FS splits up the incoming sound into multiple, narrower frequency bands. For a sound to trigger recording, it does not need to be louder than all of the ambient background noise; it just needs to be louder than ambient background noise in its specific frequency band.

For example, a bat call around 20 kHz only needs to be louder than the background noise around 20 kHz, and a bat call around 80 kHz only needs to be louder than the background noise around 80 kHz.

Additionally, the SM4BAT FS allows you to adjust the trigger level, the threshold that sets how much louder than the background noise a sound must be to trigger recording. The Mini Bat 2’s trigger level is non-adjustable.

Noisy environments

Imagine a recording environment where insects produce a loud, steady drone with harmonics that extend up to 20 kHz.

For a Mini Bat 2 to trigger, an incoming bat call would need to be louder than the drone, even if the bat call is much higher in frequency than the insect vocalization. In the absolute worst case, an extremely loud source of background noise like this could make the Mini Bat 2 completely unable to record any bats.

For an SM4BAT FS, the droning insects would still hinder its ability to record low-frequency bats; a bat call at 16 kHz would still need to be louder than the insects. However, a high-frequency bat call would not have the same problem. Because the SM4BAT FS analyzes different frequency ranges independently, its ability to trigger on sounds above 20 kHz is completely unaffected.

Key differences

The Mini Bat 2's broadband trigger mechanism is energy-efficient and effective in most recording environments. In typical use cases, the Mini Bat 2 and the SM4BAT FS record very similar numbers of bat calls.

The SM4BAT FS's narrowband trigger mechanism draws more battery power, but it produces better results in particularly noisy environments.

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