A few weeks ago someone, I think it was David Brinicombe, mentioned observi=
ng HF noise in Sennheiser MKH 20 microphones. I've noticed it too, when loo=
king at a spectrogram of a quiet environment.
This morning we did a comparison of a 3032 next to an MKH 20 on the carpet =
of an interior room, covered with some blankets. The diffuse-field HF boost=
switch was in the flat position. I used the preamps in a Sound Devices 744=
T. I posted an expanded-scale picture of the resulting spectrum at:
http://www.dandugan.com/downloads/Nature_Sounds_Photos/AT3032_v._MKH_20_noi=
se_via_744T_preamps.png
Red is Sennheiser, green is Audio-Technica. The down-sloping curve on the l=
eft is obviously ambient noise. I tried to match the levels at around 500 H=
z. I believe that above 1K we are probably seeing mic self-noise plus pream=
p noise. The "hiss" from the MKH 20 is obvious. I put hiss in quotes becaus=
e I can't hear this noise at all. It isn't trivial however. I see that up-s=
loping top end in recordings from quiet locations.
The tonal artifacts in the 3032's spectrum, especially in the range 400-1KH=
z are curious. They could be from the mic or the preamp, not investigated y=
et.
My first guess is that the MKH 20 might be equalized in its electronics to =
compensate for a naturally rolling-off HF response of the capsule.
-Dan
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