At 10:57 AM -0800 2/16/04, Dan Dugan wrote:
>Rob Danielson, you wrote,
>
>> >>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.
>> ><snip>
>
>And I asked,
>
>> >Can you explain how this specification is derived?
>
>My problem is that it seems impossible to me to specify "equivalent
>self noise" for a mic preamp in the way you do above. If your dBA
>figure refers to SPL, then it's wrong because different mics have
>different sensitivities and deliver different levels to the preamp
>for the same SPL.
Hi Dan--
I wanted to subject the mics to actual low sound levels and diverse
spectra, Sensitivity performance can be non-linear under these
conditions and potentially tied with that of the mic pre circuit more
so than under the normal bench test conditions. How much does a
consumer MD or Walkman DAT mic pre affect the performance under low
sound levels? I'll try all suggestions. Assuming the MD quality mic
pres are the primary limiting factor, next might be to test specifc
combinations of mics and outboard pres including more affordable
options so one can get a sense of what the money will buy.
>
>dB means a ratio. It has to be related to some reference level. What
>does your self noise figure refer to?
I subjected the Rodes and Sony mics and Sharp MD mic pre to the same
SPL (~24dB) and normalized the results so the relative levels of
noise produced can be heard with the same d-a. For anything lower
than 30dB ambient floor, my meter is not as accurate.
re:
>...gain matched preamps can be compared
>with a dummy mic plugged in. Five years ago we did a preamp shoot-out
>at the NSS Field Recording Workshop. I put a dynamic mic a couple of
>hundred feet out in the woods away from the camp. Mic preamp gains
>were matched with an oscillator padded down to mic level, then the
>noise levels were compared when listening to the live mic. The
>results were reported in the Fall/Winter 1999 newsletter, p. 16.
>
>Listening comparisons were made using the internal preamps in the
>Nagra IV-S as a standard. Presented in the order of quietest first:
>
>Aerco (external): quieter, maybe 2 dB
I've not seen the gain spec on Jerry's pre. Any guesses? Can he be
coaxed into making one?
>Black Audio SBMP-01 (external): a little quieter
+55dB gain
>Sonosax SX-M2 (external): a tiny bit quieter
Do you reacall if you used low gain or high gain setting? I see it
specs at +76 with high gain!
>Grace Lunatec V2 (external w/ext. battery): no significant difference
+60dB gain
>Denecke AD-20 (auditioned through DA-P1 digital input): noisier, 3 or 4 dB.
+45dB gain
>Tony TCD-D8 (internal) noisier, strange low-frequency noise
monitoring through the TCD-D8's -10dB line out?
>Tascam DA-P1 (internal) noisier, 4 or 5 dB
monitoring through the DA-P1's balance line out?
Intersting test! That's shocking that the Sony out performed the DA-P1.
I realize that recording mammals running around in the middle of the
night is not included in everyone's definition of fun and I
appreciate your patience, but for testing performance under these
situations, would there be a reason to match the gain of the pres in
the test? I need all the clean gain I can get. For example, the
AD-20 has +45dB, the Black has +55dB. With the +65dB gain I get from
my MP-2, my rural night sound files are saturated ~1%. [Mkh 20's: 10
dB(A) self noise; 25 mV/Pa sensitvity and NT1-A's: 6 dB(A) self
noise; 25 mV/Pa sensitivity]
Thanks for your suggestions!
Rob D.
>
>-Dan Dugan
>
--
Rob Danielson
Film Department
University of Wisconsin-Milwaukee
[Non-text portions of this message have been removed]
________________________________________________________________________
________________________________________________________________________
"Microphones are not ears,
Loudspeakers are not birds,
A listening room is not nature."
Klas Strandberg
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