I also tried this with 3 of my HDCDs, and found that for tracks encoded using "peak extension" you can gain considerable compression improvement by using very small block sizes. I found that --blocksize=4410 worked nicely, and on some tracks --blocksize=2205 was even better. And I'm talking like 5-10% better compression! These are the results I get for the Joni Mitchell "Blue" HDCD, with Monkey's Audio 3.99-u4-b5, wavpack 4.41.0, flac 1.2.1 (all under linux):16-bit WAVs (not HDCD decoded) 176.9 MiB mac - c5000 ( Monkey 's Audio insane) 185.4 MiB wavpack -hhx6 191.1 MiB flac --best As expected, here Monkey's Audio compresses much better than WavPack, which itself is substantially better than FLAC.24-bit WAVs (HDCD decoded), default blocksizes 338.9 MiB mac - c5000 ( Monkey 's Audio insane) 210.6 MiB wavpack -hhx6 198.8 MiB flac --best (default blocksize: 4096) I thought there was something wrong with my setup, until I saw Walrusbonzo's results , confirming mine. I can't believe how bad Monkey's Audio fared.24-bit WAVs (HDCD decoded), custom blocksizes 196.6 MiB wavpack - hhx6 -- blocksize = 4410 197.1 MiB wavpack - hhx6 -- blocksize = 2205 196.1 MiB mix of the above ( smallest encodes from each ) 197.1 MiB flac - l 12 - b 2048 - m - e - r 6 ( equivalent to -- best ) Now we're talking! Overall, wavpack with a blocksize of 4410 fares better than with a blocksize of 2205, although some tracks (4, 6, and 7) are indeed a bit smaller with the latter. Note: Monkey's Audio doesn't provide the ability to change blocksizes.