High Pass Filter Question

[GibsonGM]

Happy Good Friday/Easter everyone!     <<<<  Heck, all the REALLY sensitive stuff has already been talked about!     

I think it's cool that there are such differences in 'philosophy' in the electronics world, even to how to treat what's coming from an instrument....really, the 'argument' (from a philosophical context) is the same as "how to EQ".   I don't think there is a right answer, I feel this really depends on circuit topology, what your true intentions are (if you are going to split a signal later and treat bands differently, you probably won't cut the bass dramatically at the input, LOL).   

If I give advice like "well, you want to cut bass there", I hope it's taken as "from my point of view, based on having done this, and obtained results I liked" and not from some set of laws that are un-alterable, ha ha.    Points out, again, that there are many ways to do things, sort of like putting spice on food, and that's what makes the 'dark art' of pedal building so much fun!     

[DIY Bass]

  In this case, you only need the lowest frequency you can input which from a bass guitar is 41 Hz so 5 Hz is good for fidelity.

Ahem!  Low B is 31Hz, and I have seen that downtuned (which in my opinion verges on ridiculous, but the fact that it can happen means you may need to allow for even lower frequencies).  Personally, if I was tuning below a B I would want a high pass filter in there with a cutoff of about 30Hz and a very steep cut off - protect the speakers and amp just in case, and you are starting to be in the territory of most people hearing more of the harmonics than the fundamental in most situations anyway.

[GibsonGM]

Dude, look at: the slope of the filter...how much energy that low note has compared to higher ones.....you can set your cutoff MUCH higher than 31Hz, and still maintain clarity of that low B. 

A designer doesn't have to 'allow' for  even lower freq's.  They have to allow for the expected use of their device, which may mean a bad review by bass players, if the pedal wasn't marketed for you.

30 Hz is so low, you might as well say "let's accept ALL line noise, and set it to zero - yay!".    30 = 0.    Only issue is proportion. 

I also (well noted above) disagree, that you need to plan to "keep ALL of any freq. an instrument can make".   As I said above, I can pull a lot out of the low end of a guitar, and you'd never hear a difference - but my devices react to it.

[DIY Bass]

True, it does depend on the filter slope.  I know from experience though that you lose too much of the lows and you end up using a lot of EQ to balance it out.  You are basically then counting on amp grunt to add back in what has been taken out.  A gentle slope from 50 to 70 Hz would not be much of a problem.  A steeper slope and you are relying on having a lot more Watts on tap just to deal with the EQ.