For the Wildlife Acoustics SongMeter series, their firmware
"adds a WAV compression option called W4V that will record using various levels of compression to save card space. Resulting W4V files can be opened and/or converted back to uncompressed WAV files using the free tier of Kaleidoscope software."
From the user guide (this is for the SM4 though, note that the Micro does not have this option; I'm not sure about the Mini):
SM4 WAV file compression can be selected to record in a proprietary
compressed W4V format. The W4V format is a WAV file compression
developed specifically for minimizing loss of useful information in
bioacoustics audio recordings while maximizing compression to save on
valuable card space. W4V records the same rich meta-data as when recording
to WAV. There are three compression levels which result in the following
compression: ■ W4V-8: 50% (allows recording twice as long on a given card as compared to uncompressed WAV)
■ W4V-6: 62.5% (allows recording almost three times as long on a given card
as compared to uncompressed WAV)
■ W4V-4: 75% (allows recording four times as long on a given card as
compared to uncompressed WAV). The compression algorithm does increase the noise floor of the recording but for most bioacoustics uses, the difference between an uncompressed WAV and W4V-8 and W4V-6 will be undetectable since the noise floor in the recorded environment will be higher than the increased recording noise floor. W4V-4 will likely cause a slight increase in broadband noise in the background of the recording. It is best to experiment with your particular environment to make sure the increased noise is either undetectable or tolerable.
Wildlife Acoustics’ Kaleidoscope Viewer and Pro software can natively open
the compression formats. The free Kaleidoscope Converter can be used to
convert the files to standard WAV format for use in other software packages.
Additionally, the W4V algorithms are open-source under GPLv3 license.
Please contact us if you are interested in a commercial license.
Values (Hz): none, W4V-8, W4V-6, or W4V-4
The Audiomoth folks have tried lossless compression options but found that the compression rate ended up not being that good (i.e., didn't reduce the data a ton) for terrestrial recordings and therefore didn't pursue it further.