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Re: testing mic self-noise

Subject: Re: testing mic self-noise
From: Rob Danielson <>
Date: Tue, 3 Jun 2003 08:55:46 -0500
>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

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)

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 
Rob D.

Rob Danielson
Film Department
University of Wisconsin-Milwaukee


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