>Pardon what may be an incredibly basic question, but how would I go
>about checking a microphone's self-noise level? Is there some way to
>do it by using, perhaps, an audio editing program like Sound Forge?
>Thanks in advance
>Caesar
>
Hi Caesar et al--
I thought it might be useful to follow-up on your original question
about ways to test mic self noise. I ran my test using a 35dB bed of
urban night presence (with neighbor's fountain) at 2 a.m. as a
source. I compared a Sennheiser mkh-40 with a factory claimed 12dB(A)
of self noise and a Rode NT-3 which is spec'd at 17dB(A) by running
both thru a MP-2 mic preamp and making 24bit/48K mono sound files
through the converters in a RME Hammerfall mutliface. The NT3 was
powered by the mp2, not by the 9 volt battery option. The mp2 was
cranked to full gain for both mics.
I studied a section of the sound files where the bed was the
steadiest. The sound file created by the MKH-40 has a peak of -14.7dB
whereas the Rode's sound file over the same time period peaks at
-22.9dB. The published sensitivity of the MKH-40 is 25 mV/Pa while
the Rode's is stated as 12 mV/Pa.
I normalized both sound files to -15dB and truncated bit depth to 16
in the same step. I used a file header change in Soundhack to change
the sample rate from 48K to 44.1K so there's identical processing and
no sample rate processing involved. I linked them into a single
stereo .wav file with the MKH-40 on the left (top) ($1100) and the
Rode NT-3 ($160) on the right (bottom).
(1.9 mb)
http://www.uwm.edu/PSOA//Film/Danielson/Mic%20Preamps/MKH40MP2=L~RodeNT3MP2=R.wav
Remember, both mics are running through a $650 mic pre and through a
high quality A->D converter with no compression. From a rough test I
ran on my Sharp MT-90 MD recorder, the quality is significantly less
(more hiss) when taking an NT-3 directly into the Sharp's mic input
at FULL GAIN and through its A-D convertors and compression. I
couldn't do this later test which would give us more info about the
popular, "should I get a better mic or a good pre" question. I
don't have digital out for my MD discs and my two DAT decks recently
departed.
Rob D.
--
Rob Danielson
Film Department
University of Wisconsin-Milwaukee
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