Choosing a Sample Rate for Your Recorder¶

The sample rate is the one recorder setting you cannot fix afterwards. It sets the highest frequency the recording can contain, and it sets how much storage and battery each hour costs. This article gives the rule, a table of typical animal sound frequencies, and the AudioMoth options.

The rule¶

A recording can only contain frequencies up to half its sample rate (the Nyquist frequency). So:

Sample rate ≥ 2 × the highest frequency you need to capture, with some margin.

If you record at 48 kHz, nothing above 24 kHz exists in the file. You can always analyse a lower band from a high-rate recording; you can never recover a higher band from a low-rate one.

What your target sounds like¶

Published typical ranges. Individual species, behaviour and habitat vary; treat these as the band to cover, not exact values.

Group	Typical frequency range	Sample rate that covers it
Large mammals (elephants, large primates), thunder, infrasound	15 Hz – 1 kHz	any rate (the low end is a microphone question, not a sample-rate one)
Frogs and toads	0.3 – 6 kHz (a few species to ~8 kHz)	16–24 kHz
Most birds	1 – 8 kHz (some songbirds to ~10–12 kHz)	24–32 kHz
Crickets, katydids, cicadas	2 – 20 kHz, some species beyond 20 kHz	48 kHz for the audible part; 96 kHz if you want the ultrasonic tail
Small mammals (rodents, shrews) social calls	20 – 100 kHz	192–250 kHz
Bats — search-phase echolocation	20 – 120 kHz; e.g. big brown bat (Eptesicus fuscus) ~20–65 kHz, little brown bat (Myotis lucifugus) peak ~45 kHz, common pipistrelle ~45 kHz, greater horseshoe bat ~82 kHz constant-frequency	192 kHz minimum; 250–384 kHz for high-frequency species
Dolphins and porpoises (hydrophone)	clicks to 150 kHz	384 kHz

Sources: bat call bands from Surlykke & Moss (2000) Echolocation behavior of big brown bats and the Animal Diversity Web species accounts; bird and anuran ranges from the comparative bioacoustics literature summarised in the Ecoacoustics Glossary.

Tip

If your project is birds and frogs only, 48 kHz is more than enough and halves storage versus 96 kHz. If bats are in scope at all, you need a different recorder configuration — often a different deployment — because 192 kHz+ files are 4–8× larger and drain batteries faster.

What it costs¶

Uncompressed 16-bit mono WAV, per hour of recording:

Sample rate	MB per hour	A 32 GB card holds about
8 kHz	58	550 h
16 kHz	115	275 h
32 kHz	230	140 h
48 kHz	346	92 h
96 kHz	691	46 h
192 kHz	1,382	23 h
250 kHz	1,800	17 h
384 kHz	2,765	11 h

(Formula: sample rate × 2 bytes × 3,600 s.) FLAC compression, which Arbimon applies on upload, typically shrinks field recordings to 40–60 % of these sizes in storage, but the SD card and the upload still carry the WAV.

Arbimon's upload limits per file are listed in the FAQ; a 60-second 384 kHz WAV is ~46 MB, well inside them.

AudioMoth options¶

The AudioMoth configuration app offers 8, 16, 32, 48, 96, 192, 250 and 384 kHz. Pick the rate in the app before deployment; it is stored on the device and survives battery and SD-card changes. See Configuring Your AudioMoth for the app, and note:

Higher rates draw more current: at 384 kHz expect roughly 3–4× the battery consumption of 48 kHz for the same schedule.
The AudioMoth's microphone response falls off above ~80–100 kHz; the 384 kHz setting is for species whose calls sit below that.
A high-rate recording of birds is not wrong — it simply costs more and the Visualizer will show a lot of empty space above 12 kHz.

Checking after the fact¶

In the Visualizer, the facts line above the player shows the ceiling and the sample rate for every recording (for example ≤ 24 kHz (48 kHz sample-rate)). If a species you expected is missing from the spectrogram and its call sits above that ceiling, the recording could not have captured it. See Understanding the Spectrogram.