At 12:22 PM +0200 4/21/05, Klas Strandberg wrote:
> >Since the 957 already terminated in an 1/8th mini jack, and uses
>>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?.tok","//f2.pg.briefcase.yahoo.com/bc/rob_danielson");=bcmKTRVBNxZgHObW&.dir=/Tests&.dnm=CompareMiniDiscMicPreNoise.mov&.src=bc">http:=bcmKTRVBNxZgHObW&.dir=/Tests&.dnm=CompareMiniDiscMicPreNoise.mov&.src=bc
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 so
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 this
particular mic_ is in the ballpark of 16 dBA. [The self noise
equivalent for the MP-2 (with some conservative assumption involved)
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 note
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 addition
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 from
the recording where the NT4 is connected to the HiMD recorder's mic
pre.
The NT3's recording (apparently taking advantage of effective higher
output) exhibits about the same noise as the recording made when the
NT3 routed through the MP2. This suggests to me that a HiMD mic
preamp is more likely to introduce significant noise when the record
level is high and the mic does not have high output. This is
consistent with our theory of why the Shure 183 performed well with
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 general
"effective self noise" number because performance is the result of
speciifc mic-preamp combinations. If you need further proof of this
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.
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