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Re: testing mic self-noise

Subject: Re: testing mic self-noise
From: Doug Von Gausig <>
Date: Tue, 03 Jun 2003 08:56:08 -0700
At 06:55 AM 6/3/2003, Rob Danielson wrote:

>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

I'm still uncertain just what you demonstrated here, Rob. I looked at the 
sound way up at 14,450Hz and find the Rode did a much better job of 
capturing that faint sound, as well as the sound of the fountain. Is this 
because of the 12 vs 24 mV sensitivity?

Doug Von Gausig
Clarkdale, Arizona, USA
Nature Recordists e-mail group

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