QUOTE(shadowking @ Dec 13 2006, 14:31)

I think in normal situations you might not hear the hiss even with positive shaping +0.5 (rock,metal,pop), but when noise approaches threshold then positive shaping will be worse (classical or solo)
Thanks for the answer. This is what I learnt from earlier posts from you and from David. It's plausible to me, but to really get an opinion towards that I have to hear the problem for myself. That's why I hoped I can get a sample with known issue. Will try and find one/some tonight using low bitrate as you suggest.
The idea behind it is:
a) though I don't care very much about extreme samples like badvilbel I do care enough not to accept very audible deviations from the original. That's why I will never use a bitrate below 300kbps though b288x3 is good enough to me with regular music and even not-too-extreme problem samples as I found out last night.
I don't care about each extremely problematic sample in the same way, not so much for electronic music for instance, but samples like Atemlied are of concern to me. I absolutely dislike the deviations there.
b) On the other hand if deviations from the original sound more or less like noise from a tape recording, and if this noise has very low volume, and hopefully it is audible only in rare cases, I can accept this behavior quite well.
I guess using a positive noise shift works in this direction. Last night's experience makes it plausible concerning a) - though I have to learn more.
b) is the more critical point to me as I don't have any experience so far. But when I will try a lot of samples and won't find an issue that's experience too.
Maybe my restricted HF listening abilities are a point for a positive shift too (when trying to find problems with 16 kHz limited Helix mp3 I just found one spot with missing HF after listening to many tracks - and it was not annoying).
I once tried smart shaping and was not very happy with it. I preferred s0. Searching for this this morning I also found some warnings against adaptive noise shaping - sounds like the change in noise shaping can cause an audible issue.
To me the idea of ATH curve related noise shaping sounds more promising. But I'm not an expert.
As for the benefit of x5 for extremely problematic samples I can confirm this from my last night's experience.