At 11:29 AM -0500 2/19/05, Walter Knapp wrote:
>From: Rob Danielson <>
>
>> Sorry I'm not making myself clear. The relation I hoped to describe
>> with the phrase "noise component" is that the self noise introduced
>> by the mic is part of the total signal as a fixed percentage. The
>> noise introduced by the mic pre, at its current setting, is also a
>> fixed percentage.
>>
>> The Rode NT-4 mic has 6.5 dB(A) LESS self noise than the Shure 183
>> but the NT-4 produces a recording with MORE noise when MD record gain
>> is set at 23-- which is typical for outdoors. Taking the mic self
>> noise spec alone can be misleading, especially if one is interested
>> in recording ambience.
>
>I've pointed out that each mic also has a characteristic to it's self
>noise. Some are smooth and hide easily, some sputter or crackle or
>whatever and are easily annoying. This can negate spec differences.
The cheaper pip mic options red to have have noise that spreads
across the spectrum though. The panasonic wm-61a and the NT-4 in my
clock test exhibit this. The Shure 183 and KM-23 are exceptions.
Hopefully we'll find others.
>The
>Shure seems to be of a fairly smooth variety, can be audible but not
>really noticed. Don't know on the NT-4. Anyway, specs don't tell all.
The Sony 957 and 907 have much lower sensitivity specs than the NT-4
so tests are in order before we assume sensitivity isn't playing a
huge role in their performance too..
>
>What you are saying is that the mic sensitivity enters in as well as the
>self noise. That is true, but it's easy to get too focused on that. The
>self noise is usually controlling in terms of how quiet a site you can
>record.
It seems to me that making low noise recordings in quiet locations
always calls upon three factors.
Mic self noise: spec'd as __dB(A);
Moc Sensitivty: spec'd as __mv/Pa;
Mic Premp Effective self noise at current setting: e.g. PIP/MD gain of "23"
Without going into phantom power for now and sticking with PIP/MD/23,
BOTH self noise and sensitivity have to be quite good for sound files
with workable levels of noise.
A test placing all the PIP mics we know of head to head woud be very
interesting. Perhaps thinking about the goal of low noise field
recordings as the result of three factors, there could be some other
mic and pre amp options that we're overlooking. For example, if a
test shows that the Felmicamps FEL 3.5 mic level booster can attain
higher output without introducing as much noise as the MD mic pre,
there might be other devices or even DIY projects that one could use
for higher quality on a budget.
The next step would be phantom mics for MD line or optical in. Many
of the gear discussions I have with students and enthusiasts start
with, "I want to make quality field recordings but I only have $XXX
to spend,.."
>Unless you are comparing large sensitivity differences between
>two mics. Comparing the Shure against the MKH the story is different.
There is also significant difference in mic sensitivity going lower.
I'm pretty sure the NT-4's sensitvity of 12 mv/Pa is much higher
than the ECM-44's, 77's, Crown PZM's the Crown SASS-- this list is
quite long.
>
>> I appreciate Walt's framing of mic self noise in relation to ambient
>> sound levels because in some situations it is totally irrelevant. I
>> can set levels for a cardinal at 15' or a snow blower down the block
>> and play these recordings back without noise becoming a significant
>> part of the experience.
>>
>> However, when recording ambience under quiet conditions- mammals
>> walking through the woods at night, the hush of dusk, the murmurings
>> of a city at 3am on frigid winter morning-- the noise introduced by
>> mic/mic pre combination is a very audible component of the
>> recordings. I'm interested in the details of these spatial events so
>> when I play these recordings, I'm amplifying the original event 50dB
>> or more. In contrast, a frog or bird call played over many recordists
> > speakers might be amplified ~6dB louder during home playback.
>> Mic/pre Noise plays a very different role in these contrasting
>> playback situations. Rob D.
>
>Do not get to thinking all calls recorded were loud. When you factor in
>distance this is not necessarily so. I record barking treefrogs from
>great distances sometimes, for example. Greatest was over a mile. By ear
>it's just a pulse in the quiet background noise that alerts me, the
>telinga does better than my ears, but it's still imbedded in the
>background and often the self noise. Many times I can't get closer,
>though I do try.
Absolutely. Noise becomes a factor surprisingly quickly when I try to
record lower energy natural events at a distance. By "low energy" I
mean with open spaces where several species/events are sharing the
space-- not thunderstorms, geese, peepers,..
>
>One of the reasons why nature recording is misunderstood by music
>recordists is that they hardly have to deal with self noise. They tend
>to place more emphasis on max SPL specs. Their problem is at the other
>end, too loud. At least for rock and such like.
>
>And, yes, ambiance is where in nature recording you appreciate every dB
>lower you can get in the self noise figure.
>
>Walt
>
>
--
Rob Danielson
Film Department
University of Wisconsin-Milwaukee
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