Omnisphere can import standard, uncompressed (PCM) stereo or mono .wav, and .aif files of any sample rate with bit depths of 8, 16, 24, and 32 bit.
If you try importing a file and receive the following error message, this could mean a few things:
1.) The audio file type is not .wav or .aif
2.) The audio file is not PCM encoded
To check if a file is PCM encoded or not, you can upload your audio file to metadata2go.com and it will show you the file type and encoding (example below):
If your audio file is not PCM encoded, you can use your digital audio workstation (such as Logic Pro X, Ableton Live, ProTools) to convert the file.
To do this, drag your audio file into your DAW, then export or bounce the audio file with the corrected formatting. If your DAW doesn't give you the ability to control the 'encoding' of an audio file, try exporting as a 24 bit audio file, typically this should convert the encoding to to PCM encoding.
If your newly exported file still does not import into Omnisphere, check the audio file properties using this website once more. If the audio file type and encoding is correct, please reach out to firstname.lastname@example.org for more help.