Yeah, I think the current design makes that harder than it needs to be. You’re correct that currently the way to do it is to convert to FixedPoint values before saving (assuming that your processing is giving your floats). Originally the idea was that I didn’t want LibSndFile to do any automatic conversion, so if you read a WAV file and then wrote the contents back to disk it would be a lossless process. In practice you are almost always end up wanting to work with floats so the defaults should probably reflect that.
See this issue with some of my thoughts on it:
https://github.com/JuliaAudio/LibSndFile.jl/issues/23