Noise leel is very low. Best to set recording level at the start - about 3 Db below 0. The gain can be normalised afterwards via "Audacity" with no discernable increase in noise level.For interest I did post a recording made on the H4. This was to illustrate the sound of the Ymaha S6 rather than to display musical ability. See:https://www.pianostreet.com/smf/index.php/topic,24492.0.html
I've used several different mics and things, and I have to fill in here with some observations:The BY FAR best mics I've found for a low price is Behringer ECM8000!They are extremely cheap, I guess $40 a piece or so.The reason they are so good for recording piano/grand piano is that they are omnidirectional measurement microphones, i.e extended frequency response (lower than 20HZ and higher than 20kHz), extremely linear (almost no colouration), and a miniscule diaphragm (low mass, fast transients).They really GROWL in the bass and give a really natural high treble.Their sound characteristics are reminiscent of B&K, or DPA (as they are now called) because of similarity in design, but of course not as high quality as them.In other words, the sound is a bit like Murray Perahia's recordings (with all the obvious differences, of course!)Only issue is that they have bit more noise than large diaphragm mics. Otherwise, they work on phantom power too. Studio Projects B1 and B2 are a bit more fun in a way, because of their own sound and the warmth etc, and with a pair of B2's you also have almost all the stereo techniques to try, i.e. XY, ORTF, Blumlein, AB, M/S. That's very handy when recording chamber music etc, but for a superior sound for piano solo, ecm8000 are the easiest to use and the greatest sounding. On a budget, of course!
"2) Overload capabilitiy is very limited, which can lead to severe distortions with some pianos played on forte."Maybe if you put them right on top of the strings and play fff (which I haven't checked), but in normal use they are NOWHERE near overloading!
Compared to Studio Projects B1-B3, C1-C3, or any other large-membrane mic they have very much in common with B&K/DPA (why did you mention gefell?), or there is something severly wrong with my ears:). Mind you, I'm not talking hair-splitting differences here, just sonics at large.
Never tried the Jecklin, but I think for stereo experiments multi-pattern large-membrane mics have many more possibilities, see my post above.
"1) Too much of internal noise"Maybe for professional release, but for demo or posting high-quality rec here, their noise-level will be virtiualy inaudible.
Just a quick quizz then...how easily can you tell which is which? Beethoven Tempest, start of 2nd mvt. One of them is that famous pianist, one is moi..