wrote:
>All: This preamp question comes up now and then.
>
>Has anyone really investigated how bad the mic inputs are of different MD'=
s
>and DAT's?
>Has anyone tested how sensitive a microphone must be, (output voltage) to
>run over the noise of the standard MD mic amps??
>
>My little idea is that there is not much use of preamps (to improve noise
>level) as most microphones today have either enough output voltage or make
>so much self-noise that a preamp won't help.
>
>So: What is the advantage spending lots of money on a preamp and how do yo=
u
>know that for sure??
Don't you think that most folks who are talking about noise are
trying to record soft sounds? With your dish and a nearby healthy
bird at 30 yards, your Portadisk mic pre gain must be well below max.
Going the extra mile to lower noise comes from people interested in
recordings where the local acoustics are part of the image. For
their surround projects, my students are moving mics away from sound
sources to capture more of the space-- a very different practice than
trying to isolate all sounds except junk "presence" tracks of 20
years ago. Of course, this is not a new desire or technique, but it
is much more common and people have modest budgets. The MD mic pre is
the weakest link. There are mics with high output, 6 to 18dB(A) self
noise, the ability to record in high humidity and wind for $200.
Some numbers that have proven to be very useful estimates for us are:
Consumer MD mic pres with the gain set at maximum have an equivalent
self noise of 20-25dB(A).The Walkman DAT's are in the same
neighborhood.
Tascam DA-P1 with the mic gain set at maximum has an equivalent self
noise of 12-14db(A). Based on comments on this list and others, the
Portadisk mic pre at full gain might be around 10-12dB(A) but I've
never had one to compare.
The MP-2 has a self noise of about 4-5dB(A)
The Audio Buddy Mic Pre has an equivalent self noise of about
12-14dB(A) when the gain is set to max.
Bob Cain (micbuilders llst) derived one or two of these numbers, I've
ear-tested them with many mics and have found them pretty accurate in
determining whether an investment is likely to lower noise. Being
able to use the line input of an MD recorder is itself a big
advantage. Even a 25dB(A) mic will sound a bit cleaner using a $300
Mic pre like the Edirol UA-5. A mic with 18dB(A) self noise through a
decent pre will sound considerably cleaner. Some of us use pres in
the 5-12dB(A) range to better enjoy the low noise of great mics-- and
that is why somone would consider a $700 mic pre for an MD recorder.
It's a bit overkill, and it seems odd, but there aren't too many
alternatives.
Many of the lower cost and better mic pres have maximum gain in the
neighborhood of 45-55dB which means 10-15dB less gain than the folks
cranking their MP-2's to the max. In quiet settings, that's huge.
I've been trying to get the DC power and phantom power issues solved
with the Audio Buddy which is a very decent sounding $90 pre with
60dB of gain. That would fill a big void with the $200 low noise mic.
>And for which microphones??
It would take quite a bit calculation to put all the mics and pres on
one standard because, as you point out, its not just noise but mic
output/sensitivity too. We'd also need apples and apples numbers for
the pres and the -10dB line inputs.
As a ballpark guide, the Rode NT-3 seems to consistently ou-tperform
the MT-90 mic pre. This mic has 17 dB(A) self noise and 12 mV/Pa
sensitivity. In theory, there's no point in spending more on a mic
that specs better than this without considering a better recorder or
a mic pre. When you consider that many nature recordists and natural
space recordists find their way to an ECM-MS957 stereo with 25 dB(A)
self-noise with and considerably lower sensitivity or DIY Panasonic
WM-61a capsules with 32 dB(A), its easy to see why people start
imagining what another few hundred could do,.. For me, a $90 portable
pre with 12d(A) self noise would mean students would have much
better access to low noise recording rigs.
Rob D.
--
Rob Danielson
Film Department
University of Wisconsin-Milwaukee
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