What is interesting is the "1khz tone" and then the "passband" selections. Some have different approaches to implementing a low-pass filter. Not all of them go up to 22,000HZ. Two of the foobars cut off before 22,000 though the Foobar SSRC source goes all the way up to 22000. If you look at wavlab 5.0 to 6.0 there is quite a bit in difference. Looks like WL changed some routine from 5.0 to 6.0. R8brain free filters the top end too...quite interesting results. Some think that the "weiss saragon" and "mbit+" - available in all Izotope Ozone products are the best two.
Can we hear the difference? Not many can hear up to 22,000hz or anyone. Though ran same file with R8brain free and Mbit+ and the highs seem more cut off in r8brain free then mbit+. Not saying I can hear up to 22,000 HZ. Though if you listen in playback one has more high end then the other. Would say that going up to 22,000hz adds to the high end profile even though we can not really hear those frequencies. This is the experience had with my ears and my playback system.