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HiMD Mic preamp noise

Subject: HiMD Mic preamp noise
From: Rob Danielson <>
Date: Wed, 11 May 2005 09:18:23 -0500
In addition to being able to compare high gain
performance of some of the popular PIP compatible
mics, my other hope was getting at a ballpark
"effective" self noise figure for the consumer
PIP mic pres. The later goal may not be possible
because there's evidence that the mics are
performing inconsistently with PIP mic pre
circuity. We're seeing mics perform with greater
and lesser sensitivity than they should and doing
so repeatedly, with the same measured
differences. The Shure and Rodes I've been using
are all new mics. My students first pointed out
the NT-4/NT-3 output discrepancy to me which all
three tests confirmed.

So far, we've only tested mics with moderate self
noise. Klas's tests have repeatedly brought the
"effective" MD pre noise level down to less than
14dBA with the EM-23. My recent test with the
NT-3 sets it below @17dbA.  Its possible that
there are some lower-cost, high performing
mic-pre combinations that recordists are not
taking advantage of because we've only tried the
obvious, PIP-compatible mics.  Does anyone have a
48 volt phantom power supply that I could borrow?
Best if it was battery-powered and stereo but AC
powered and mono would suffice. Such unit would
allow me to test the MD mic pre with low noise
mics.

If a test were to find the MD internal mic pre to
be "up to the task," phantom power modules are
fairly small and quite a bit cheaper than an
outboard pre like the MP2.  The  Denecke PS-2
phantom module goes for less than $200. The Rode
NT1-A's (6dBA self noise) are $200 each. This is
one possible combination which might provide
recordings with significantly lower noise for
about the same price as one, used MKH 40 mic-- so
it would be interesting to test.

The three tests I've done seem to suggest the
gain on the Sony HiMD NH-900 is on par with the
MP2's which is very good news.  Rob D.

  =3D =3D =3D

At 2:01 PM +0200 5/11/05, Klas Strandberg wrote:
>A Telinga microphone boosts sensitivity and low noise. It sacrifices high
>sound pressure level and in one case (stereo DATmic) also linearity.
>
>Other mic's don't do that. Therefore, if you want to combine "the Telinga
>qualities" with high sound pressure level and linearity, - you are stuck i=
n
>the Sennheiser MKH system. There is no way around this problem.
>
>I don't know about the Rode mic's, except that they are made by a Swede wh=
o
>emigrated to Australia and sold here, too, in shops for musical instrument=
s
>and vocals.
>
>What I know about microphone tests is that is is soooo easy to make errors=
.
>Even the most careful tests which I (and J=F6rgen) have made, have proved =
to
>be wrong after a few days only. It is like you have to "get acquainted"
>with a certain microphone over a long time before you can judge about it. =
I
>have listened to mic noise one evening and judged it as okay, next day I
>find it too high... And vice versa!
>And most of the tests which I do have to be repeated over and over again.
>Only when I get the same result at least five, six times - then I am
>pleased with the reliability.
>
>I can only claim two things:
>
>If you hear microphone noise, then you cannot lower this noise by using a
>preamplifier. It is there, and all you can do is amplify it.
>If you hear MD / DAT amplifier noise, you have the wrong microphone for
>nature sound recording. Or - rare - you have a very, very bad microphone
>preamp, must worse than any common MD mic input.
>
>I tested again today: Used a 10 mm PIP electret and a EM23PIP into
>different Sharp MD's which I have + the Edirol R1. The noise I could hear
>came from the microphone FET and not from the MD / Edirol mic input amp.
>
>A preamp into the line inputs will only amplify this FET noise.
>
>I don't deny that others have other experiences, but I can't explain it.
>
>When reading data sheets with noise figures and frequency curves, don't
>forget that those figures were measured with a brand new microphone,
>inside, room-temperature and a suitable humidity. Age, low temp, impact
>from use in humid areas, dust and bacteria (even fungus!) will affect thos=
e
>figures by many db.
>
>Klas.
>
>
>
>At 20:07 2005-05-09, you wrote:
>>Hi Klas-- I apologize for my error.  Were you able to download the
>>test?  There's a noticeable increase in noise with the NT-4 that I'd
>>like to hear your thoughts about.  The MP2 preamp does seem to lower
>>the noise with the NT-4 and the curious thing is the NT3 and Nt4 both
>>have very similar self noise (16 and 17dBA) and exact sensitivity
>>specs (12dBA). I can email it to you too, its 2.3 mb.  Rob D.
>>
>>At 6:47 PM +0200 5/9/05, Klas Strandberg wrote:
>>  >At 23:55 2005-05-04, you wrote:
>>  >>I went down to fix dinner and realized that my logic is wrong about
>>  >>being able to deduce any Mic Pre noise figure from the test. Sorry.
>>  >>With the NT3, if the noise through the HiMD mic pre and the
>>  >>workaround MP-2 is the same, what we're hearing is likely the noise
>>  >>just from the NT-3.,..I have to go back to making dinner, but why
>>  >>does the NT-4 through the workaround MP2 have less noise? Where would
>>  >>the noise be coming if not from the HiMD mic pre?  Rob D
>>  >
>>  >
>>  >How wonderful isn't it with people who has such a free-running brain t=
hat
>>  >it realized a previous error while fixing dinner....
>>  >
>>  >I still don't know for sure what is right and wrong in this topic, but=
 I
>>  >hope that my brain will solve it while making dinner next time. Have t=
o
>>  >wash my car tomorrow. Perhaps then...?
>>  >
>>  >Until then I repeat: If you hear noise, you can never lower this noise=
 by
>>  >using a preamp.
>>  >
>>  >Klas.
>>  >
>>  >
>>  >
>>  >
>>  >>Rob D: wrote and realized soon afterwards,..
>>  >>
>>  >>  >
>>  >>  >
>>  >>  >At 12:22 PM +0200 4/21/05, Klas Strandberg wrote:
>>  >>  >>   >Since the 957 already terminated in an 1/8th mini jack, and u=
ses
>>  >>  >>>plug-in power? Or maybe it's battery operated? I'm not sure how =
much
>>  >>  >>>you'd gain by adding a preamp. I think we're mainly referring to
>>  >>  >>>phantom powered mics using external preamps. That being said, I =
know
>>  >>  >>>often the minidisc mic input isn't the cleanest, and if you can =
go in
>>  >>  >>>line level, you'll bypass some of the noise.
>>  >>  >>
>>  >>  >>
>>  >>  >>I clam that that statement is common but wrong.
>>  >>  >>Give me some proof!
>>  >>  >>
>>  >>  >>Klas.
>>  >>  >>
>>  >>  >
>>  >>
>>    >m("sbcglobal.net/vwp2","//f2.pg.briefcase.yahoo.com/bc/rob_danielson");=">http:=
?.tok
>>  >>
>>=3DbcmKTRVBNxZgHObW&.dir=3D/Tests&.dnm=3DCompareMiniDiscMicPreNoise.mov&.=
src=3Dbc
>>  >>  >
>>  >>  >Right-click on the paper-looking document and select, "Download
>>  >>  >linked files as,.." option.
>>  >>  >
>>  >>  >I've uploaded the above 2.3 mb QuickTime movie that compares the
>>  >>  >resultant noise from Rode Nt3 and Nt4 mics using a HiMD mic input
>>  >>  >jack and the same mics routed through a Sound Devces MP-2 outboard
>>  >>  >preamplifier into the HiMD's line input. The recordings were made =
at
>>  >>  >16/44.1; the QuickTime movie has an IMA:4 compressed sound track s=
o
>>  >>  >that more people can download it. Again, these tests are for quiet
>>  >>  >location recording situations where high gain is more likely to be
>>  >>  >used.  The files are well saturated and loud, be sure to adjust
>>  >>  >playback volume to a comfortable level
>>  >>  >
>>  >>  >To my ears, the NT3 presents a fairly close match between internal
>>  >>  >and external preamp noise which suggests to me that an "effective
>>  >>  >self-noise" rating for the NH-900 HiMD recorder's mic pre _with th=
is
>>  >>  >particular mic_ is in the ballpark of 16 dBA. [The self noise
>>  >>  >equivalent for the MP-2 (with some conservative assumption involve=
d)
>>  >>  >is in the area of 5dBA, so its very unlikely to be adding noise.]
>>  >>  >
>>  >>  >I say only for "this particular mic"  because, as we found before,
>>  >>  >sensitivity (output) and other factors come into play. You will no=
te
>>  >>  >that I had to boost the playback level of the NT4's recording 14dB=
 to
>>  >>  >match the playback level of the NT3's recording.  Even though both
>>  >>  >mics have very close self noise specs (16dBA for the NT4 and 17dBA
>>  >>  >for the NT3), the noise component in the NT-4's recording is also
>  > >>  >increased 14dB to match playback leve with the NT3's.  The additi=
on
>>  >>  >of noise from the HiMD mic pre can be confirmed by looking at the =
NT4
>>  >>  >signal routed through the MP2 where we hear less noise than that f=
rom
>>  >>  >the recording where the NT4 is connected to the HiMD recorder's mi=
c
>>  >  > >pre.
>>  >>  >
>>  >>  >The NT3's recording (apparently taking advantage of effective high=
er
>>  >>  >output) exhibits about the same noise as the recording made when t=
he
>>  >>  >NT3 routed through the MP2. This suggests to me that a HiMD mic
>>  >>  >preamp is more likely to introduce significant noise when the reco=
rd
>>  >>  >level is high and the mic does not have high output. This is
>>  >>  >consistent with our theory of why  the Shure 183 performed well wi=
th
>>  >>  >22.5dBA noise in the prior test with its high sensitivity of 42 mv=
/Pa.
>>  >>  >
>>  >>  >So, there is no simple way to put MD mic preamp noise into a gener=
al
>>  >>  >"effective self noise" number because performance is the result of
>>  >>  >speciifc mic-preamp combinations.  If you need further proof of th=
is
>>  >>  >phenomenon, according to Rode, the NT3 and the NT4 have equal
>>  >>  >sensitivity (12 mv/Pa).  Their output impedance is also matched at
>>  >>  >200 ohms.
>>  >>  >
>>  >>  >I tested the mics from the first test again and I feel the results=
 of
>>  >>  >the first test are very reliable. That's is available  as a small
>>  >>  >.mov now:
>>  >>  >
>>  >>  >http://www.micbooster.com/movies/TransMic&PreTestSor3_IMA.mov
>>  >>  >
>>  >>  >People commented on the appreciable leap in quality that happened
>>  >>  >with the NT1A/Mp2 in the first test so I'm testing some higher end
>>  >>  >mic-pre combos. Rob D.
>>  >>  >
>>  >>  >
>>  >>  >
>>  >>  >
>>  >>  >
>>  >>  >
>>  >>  >
>>  >>  >"Microphones are not ears,
>>  >>  >Loudspeakers are not birds,
>>  >>  >A listening room is not nature."
>>  >>  >Klas Strandberg
>>  >>  >Yahoo! Groups Links
>>  >>  >
>>  >>  >
>>  >>  >
>>  >>  >
>>  >>
>>  >>
>>  >>--
>>  >>Rob Danielson
>>  >>Film Department
>>  >>University of Wisconsin-Milwaukee
>>  >>
>>  >>
>>  >>
>>  >>"Microphones are not ears,
>>  >>Loudspeakers are not birds,
>>  >>A listening room is not nature."
>>  >>Klas Strandberg
>>  >>Yahoo! Groups Links
>>  >>
>>  >>
>>  >>
>>  >>
>>  >
>>  >Telinga Microphones, Botarbo,
>>  >S-748 96 Tobo, Sweden.
>>  >Phone & fax int + 295 310 01
>>  >email: 
>>  >         
>>  >
>>  >
>>  >
>>  >
>>  >
>>  >"Microphones are not ears,
>>  >Loudspeakers are not birds,
>>  >A listening room is not nature."
>>  >Klas Strandberg
>>  >Yahoo! Groups Links
>>  >
>>  >
>>  >
>>  >
>>
>>
>>--
>>Rob Danielson
>>Film Department
>>University of Wisconsin-Milwaukee
>>
>>
>>
>>"Microphones are not ears,
>>Loudspeakers are not birds,
>>A listening room is not nature."
>>Klas Strandberg
>>Yahoo! Groups Links
>>
>>
>>
>>
>
>Telinga Microphones, Botarbo,
>S-748 96 Tobo, Sweden.
>Phone & fax int + 295 310 01
>email: 
>         
>
>
>
>
>
>"Microphones are not ears,
>Loudspeakers are not birds,
>A listening room is not nature."
>Klas Strandberg
>Yahoo! Groups Links
>
>
>
>


--
Rob Danielson
Film Department
University of Wisconsin-Milwaukee


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