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.
> 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.
> 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.
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.
Walt
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