It would appear that several DAWs built for OS X (Digital Performer, DSP Quattro, possibly even) Logic) are capable of processing audio internally using 64-bit samples. However, I can’t get an AU to build that will do that. My VST build seems to be working fine.
It would appear that in juice_AudioUnitPluginFormat.mm support for ‘processBlock (AudioBuffer…’ is missing.
Is it possible to build a double precision AU format plugin ?