At 7:02 PM -0500 2/17/04, Walter Knapp wrote:
>From: Rob Danielson <>
>>
>>
>> At 10:57 AM -0800 2/16/04, Dan Dugan wrote:
>
>>>>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--
>
>Which is why it's much better to determine things at this level on a
>case by case basis with actual field recording experience. There are too
>many variables for bench testing to tell a lot. Spend a season recording
>with some combo and you will know far more.
For sure. I'm lucky in that I've become familar with the mics and MD
pre combinations I cited through the experiences and recordings of
many students. I'm addressing worst-case performance issues of the
lower cost gear options because they and others are mostly interested
in recording acoustic spaces and the natural, quieter ones have more
going on musically and biologically.
For this type of recording, I tossed out this a overly-simplified use
of "self noise" numbers for beginners
Mic or Pre equivalent self noise
MS-957 25dB(A)
MiniDisc Internal Mic Pre 22dB(A)
Rode NT-3 17dB(A)
There are other, lower-cost self powered mics and high gain field
portable Mic pres that would be useful to include (thru a common
field test) like
Sennheiser ME62 17 dB(A) 20 mV/Pa
Audio Technica 825 stereo 24 dB(A) ?
R=F8de NT4 stereo 16 dB(A) 12 mV/Pa
Audio Buddy (DC Mod) StereoMicPre 12dB (A)
and others??
I'm trying to address mic/pre combinations (internal or not) for
recording location ambience on a budget-- people who will invest
$500-$1000 for a whole field rig but not in a single mic, external
pre, or recorder. I like to see more of these folks out there having
fun and getting better results. Its the frugal/DIY side of me talking.
>
>> 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.
>
>Not only mic sensitivity can vary under different sound conditions, but
>the noise a pre produces may not be consistent between different settings.
>
>If one is trying to run a very quiet mic with consumer MD pre's then the
>pre could be limiting. You have a mismatch in equipment. You have a
>choice of upgrading the recorder or sticking in a separate pre and
>hoping that's enough. Against going with a recorder with suitable pre's
>you have a limited amount you can spend on the combo of consumer
>recorder and pre before you have reached the price of replacing the
>whole thing.
>
>Judging from my experience with going to the Telinga while continuing
>with the Sony MZ-R30, I'd say it's mostly mic that counts, pre is only a
>small part of the equation. And not getting the quality mic, no pre will
>overcome what the mic did not do right. What this says is you might or
>might not be getting a pre, but for improvement you must get the mic.
For loud sounds/settings, I agree, this is probably the case.
>
>> Intersting test! That's shocking that the Sony out performed the DA-P1.
>
>Others have reported problems with DA-P1 pres.
>
>> 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]
>
>It might be better to look at it as dynamic range. The self noise sets
>the floor of the dynamic range, the mic sensitivity sets the top of the
>dynamic range for any given site. You hand that to a pre, you cannot
>increase the dynamic range, but you can position it within the available
>digital dynamic range, which is much greater than the site's range. And,
>of course if there is not enough clean dynamic range in the pre to
>position the site dynamic range then the pre can make it worse.
I'm at the noise floor of pretty much with every component. I can
hear an increase in broadband noise above 2K when bit
depth/saturation drops lower than 1%. Maybe more very, very clean
gain to get me up ~3% saturation might help, but probably only a tiny
bit. Recording at 24 bits is helping there already. Dynamically, I
lose some stuff off the top like a beaver felling a tree 60-80 yards
away or deer sniffing the zep, but those over-mod disappointments are
rare.
>If the combo of sensitive mics of low noise is not getting it, then you
>have to change mics or figure out how to get closer. At your stated 24dB
>site, you are going to be running against a small dynamic range due to
>the mics alone. A more sensitive or quieter mic would help, but you are
>running out of mic options. Try a MKH60 maybe as it has lower self noise
>and greater sensitivity. The only other equipment way out of this
>problem is to get more gain
>before the mic. That's a parabolic or one of the boundary mics. Like the
>SASS, though that only get's you about 4dB extra.
>
>Note if you are recording in mono, there is one other way out. You don't
>get rid of the noise, you make it less noticeable to the listener. This
>way is stereo, as in a stereo field our natural filtering abilities will
>allow us to ignore noise better. The sounds we want will have a location
>and we can ignore other locations, or sound that's everywhere. We can't
>do that in mono. In fact switching from mono to stereo may be one of the
>best ways to deal inexpensively with self noise of consumer gear.
That's true, by turnng down the mental comparative processes. Yet the
same comparative processes can open up so much, they're hard to
sacrifice. In surround, I cut down to mono for some middle ground
and foreground elements--especially when the source is moving.
Rob D.
=3D =3D =3D
>
>Walt
>
>
--
Rob Danielson
Film Department
University of Wisconsin-Milwaukee
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