- If I select crossfade loop it successfully calculates in the transitions. But can I somehow control the lengths of the transition by myself? For example for long, evolving strings it could sound better to have a really long transition…
The crossfade is calculated from the total length of the sample, or the selection you’ve made (if any). Transition is roughly one third of that, if I recall correctly.
So for good results, it’s often better to work with a really long sample (longer than the xfaded sample).
- Is there an option to precisely auto-find null passings for proper, clickfree looping? I currently doing that manually.
I guess you know about “snap to zerocrossing”. But even then, the problem is often that you can’t find a precise zero-crossing across both channels.
If this is really important, and xfade for some reason doesn’t do the job, then manual editing or splitting each channel into separate samples is the only way I can think of.
- What are the weapons of choice / tools for improving those workflows? I already forgot…
One of the hidden gems: afta8 has created thistool with an alternative crossfade implementation 
- Is there a simple way to process a sample using renoise fx directly in the editor, without bouncing or something? And if so, can I process all samples at once?
Sure, process FX is possible in the sample editor. Not batch capable, AFAIK.
- I am kind of stuck with the 3.1 filters in the sampler: Which one do not affect the sound at all at cutoff 100% and rez 0%?
Not sure which one is the most neutral. It also depends on the character you’re looking for when the filtering actually kicks in?
- Would love to have lp and hp fitler in serial, per note, is that possible?
Currently, only a single filter can be used in modulation. It’s a good point, though.
I usually manage by adding some EQ or filter in the FX section to contain sharp frequencies.