-121dBu seems plausible to me. Logarithmically and test bench
challenged I've been using my ears to come up with a figure for the
HiMD mic. The Equivalent Input Noise for the 722 is spec'd at -130dBu
max @150 ohms, A-weighed. Assuming I can consistently hear 1dB
difference, -121dBu might be ~9 audible gradations of noise. I can
divide the audible difference between the HiMD mic pre and the 722
into 5 or 6 steps. That implies to me that the HiMD mic pre is in the
same ballpark or perhaps a bit quieter. When I pass my MKH's through
the Rolls->HiMD, all of the noise I can detect seems to self noise
from the MKH-30/40. Putting these clues together, I've been imagining
the EIN to be ~ -123dBu for the HiMD. I believe I can detect the HiMD
pre noise with the NT1A's. Its funny, I switched my major from
physics to art when I was a junior in college. I decided I wasn't so
much interested in things I couldn't also experience. Perhaps too
harsh a judgment, but I truly felt the world needed more art.
Ironically, as my sensitivity has improved (or disproved?), I have to
rely more and more on folks who actually know the science. My thanks
to you and others who put up with this! Rob D.
At 9:54 AM +0000 1/9/06, Raimund Specht wrote:
>
>I calculated the -121dBu figure from the Marantz literature
>(Microphone input sensitivity: 1.2mVrms =3D -56dBu) and the microphone
>Signal-to-Noise ratio (65dB(A)). So, it is just an approximate figure.
>A relative test which a SD722 roughly confirmed that figure. As Dan
>Dugan pointed out, this calculation would actually require the dynamic
>range figure (which is not specified by Marantz).
>
>It is also important to note that the input referenced noise level of
>a recorder also depends on the source impedance of the microphone (low
>impedances provide lower noise levels).
>
>Regards,
>Raimund
>
*
--
Rob Danielson
Film Department
University of Wisconsin-Milwaukee
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