It seems that AudioDataConverters class isn’t public (I didn’t found the corresponding inclusion in juce.h and related files).
In fact, I’d like to use some of its functions but find a bit strange to need to include juce_AudioDataConverters.h in my app code as i already include juce.h.
oops! I use a script to generate the juce_app_includes.h file, and it looks like it’s not adding the audio/dsp directory. You can add the extra line to that file yourself to include the converters. Thanks for spotting it!