Wouldn’t it be expected if it’s creating more than the FLAC? (but you’re right it is very slow). But also, trying it here, the HD lossless is about twice as fast in Wavelab 8.5 and Wavelab 9 than in 9.5.35 using the same file and AAC-HD lossless factory preset. It consistently gets slower halfway through on 9.5.35 here. I wonder, is that because of 64 bit float processing?