FWIW my C12 is not noisy. It has about the same level of noise as my point to point U47 build. Do you hear the "pink noise" in the acoustic guitar clip I posted?
Can't tell from the clips you posted, they are edited(cutted) so short. Leave a few seconds before or after the recording source and then I might hear it,...or not....
Now, don't imagine that my builds have a hurricane inside them wich I call "kind of a pink noise", it is something subtle, but it is!
Any mic has noise, but actually, I found my Sennheiser e906 was much noisier than this tube mic once I turned up the preamp gain to get it as loud as the C12.
Turning up the preamp gain increases preamp self-noise and so will increase noise in every mic(at least this happens with my preamps : SCA, JLM, DAV). A fair comparison would be done at the same preamp gain level/output level, and then lowering the loudest mic level into your daw to match levels.
Yes, turning up the preamp will increase noise, but not as much as it will boost the actual audio signal, assuming the preamp is any good.
In the spirit of your posts, I decided to do a little noise shootout. C12 versus Sm7b. I leave a couple seconds of room tone, then play a short progression, then let there be room tone.
Test 1: Get the same volume going into the A/D. C12 pre is at 7. Sm7b pre is at 10. Don't adjust levels in DAW.
Which is noisier?https://copy.com/DB70ztYx8Esxhttps://copy.com/JEQ1fN8Q6TAx
Test 2: Same preamp gain. Turn the louder mic down in the DAW to the same volume as the quiet mic. Which is noisier?https://copy.com/TKWY4jdXDp1Zhttps://copy.com/2mZNiZAFA1Si
Should I do this test not with an SM7b? Unfortunately all of my LDC mics are tube-based, so i can't compare noise with a FET LDC. I wont post the files but I just did this same test with my DiY U47, and the C12 is indeed a tiny bit noisier. Not pink noise, but a more noticeable hum. Nothing compared to the Sm7b, though.