There is DIY hardware FM-synth, PreenFM2. Since last firmware it supports loading of custom user waveforms from USB in such format. So i thought Renoise’s sample editor with it’s features + LUA is really good for this task.
Now if you do want to go from a renoise mono sample to a text file (in that format) I’ve knocked together a possible quick hack tool for this. It adds ‘Sample to Text’ to the sample menu