The Audio Ease approach to the anti-aliasing filter is this: Attenuate as fast and as severe as you can, right after the new highest possible frequency (nyquist brick-wall). The reason for this is that real world audio material is pink in shape, which means it contains more energy at 27 kHz then at 47 kHz. It makes sense to suppress 27 kHz at least as much as 47 kHz. Tweakhead filter curve falls of of slowly and keeps on going, while BarbaBatch drops to -120 dB immediately and then attenuates further to -132 dB at 48 kHz.

For starters it is important to show that this is widely adopted philosophy. Digidesign also makes their anti-aliasing filter slope steeper with each step up in quality. The converted sweep wavefors reveal the shape of the filter slopes:

ProTools Good	ProTools Better	ProTools Best
ProTools Tweakhead	Barbabatch quality 2 (good)	Barbabatch quality 3 (best)

Then we zoom in vertically to check how much the filter actually attenuates the audio above 22050 Hz. (Digidesign calls this stopband attenuation in their specs).

BarbaBatch:

Barbabatch arrives at an attenuation of 120 dB at 23 kHz. and remains quite steady from that point on, to end at -132 dB at 50 kHz.

ProTools Tweakhead:

Tweakhead reaches -120 dB at 32kHz, going on to become silent.