From: Rob Danielson <>
> Thanks for taking time to make the pictures and pose good questions.
> Its fascinating to consider sources for the banding and other things
> going on. Neither of us has time to really get to the bottom of it,
> but here are some of my thoughts you can read over when you get rhe
> chance.
I thought that was the purpose of the test recording, to critically
evaluate the mic. Otherwise I'd be doing like so many folks, just
enjoying the night sounds in it. All of your options may have some
bearing on what I'm hearing, I'd considered them. My best opinion is
this is not natural sound caused though it contains imbedded natural
sound. It will take much more recording for a clear picture to emerge.
> (1) The approximately 9 bands 5K and band ~12k. Seems like these
> would have to stem from a combination of mic self noise, high
> frequencies from the environment and possibly dithering noise. To my
> ear, the "zizz" I'm hearing above 6K is roughly a 50/50 blend of mic
> noise blending with very subtle sounds. Horizontal sonogram banding
> in this range around this much water under a canopy of leaves is
> expected. Are the mics representing these high frequencies as well
> as we can imagine? Clearly not, but we're asking a lot out of the
> recording system (mic, pre, medium etc). Most of the of the total
> amount of sound energy is concentrated below 160Hz, so most of the
> resulting ~1% file saturation of the original 24/48K recording
> (background ambience only) results from energy from 160 hz and
> below. Its hard to interpret with one color acrossa good part of
> sonogram range, but it looks like the bands above 5 K could be around
> -30dB to -40dB relative to this those at 50Hz. If the ambient
> background sound level is around 25 dB (a workable estimate based on
> a test with a good meter once and the resulting saturations) and the
> difference between the low energy and that above 3k is only 20dB,..
> the environmental sounds or noise, take your pick, are very close to
> the self noise rating of the mic.
>
> (2) The ~7 horizontal bands between 83 and 500Hz. A harmonic tone
> can heard it whenever its really quiet in both mics. In a short
> snippet, it does sounds a lot like a very distant highway-- like
> truck tires. I checked places when a truck comes through valley and
> there's no point that really sounds the same and when the sound
> character is most like this drone, the file saturation is much, much
> greater. Take a look at the "checkered" pockets or amplitude clusters
> in the bands between 80-500.They're thicker (longer) at the lowest
> frequencies and they get continuously shorter each band up where they
> blend into the picture resolution on my screen around 600Hz. This
> pace of the pulsing is quite structured and if its noise from mic
> moisture or even distortion noise, its very unlikely to be so similar
> in both mics. The orange spikes at the bottom have much less of a
> pattern- more like one would associate with noise and the lower
> spikes correspond with higher spikes too. Accounting for these clues
> and the way it sounds, I take these bands between 83 and 500hz as
> mostly a blend of distant low hz energy being reinforced by local
> acoustics. The other part might be overtones produced by way these
> particular mics "bounce" in response to very low level, low frequency
> sounds. All mics have a "bounce" like this in my experience.
>
> What low Hz energies? There's a visitors center with HVAC ~ 1/5 mile
> away, a truck garage/farm behind the dam about 1/5 of mile, a new
> dairy/cheese factory on the hill a half mile away and close edge of
> LaFarge (pop 700) is 1.5 miles away. I'm not discerning any one
> source, but compressors at the dairy/cheese factory is my best guess
> for the harmonic structure. Can you see a 60HzX component? Your
> sonogram app spreads out the range as well as mine can. I know its
> not a truck idling anywhere near because I have heard hours of that
> on other recordings.
You got me, it's not a idling truck for sure, the general sound
characteristic is that of fast moving traffic, like a freeway. But
industrial equipment can do this too. Note that low frequencies travel
well, if it's a sound that was there, it's a long ways off. The sound is
so steady it's not individual vehicles occasionally. Many vehicles, or
steady running industrial. If there is a 60hz component it's not dominant.
I could actually adjust the sonogram software to just look at that area,
but I'm not sure it would help.
At my house, a gas turbine power plant, 5 miles away, is a dominant low
frequency sound, particularly if I use the SASS/MKH-110. Closer to it
the folks get the higher frequencies too.
> The local acoustics, primarily, would be created by the 12-15' high
> limestone river bank on the close side and 4-9' mostly bare clay bank
> on the far side, a stand of small trees along the far bank, a stand
> of pine trees behind the mics and a dense deciduous canopy over the
> river.
I take it the mics were on normal height tripods? The high tripod
approach would give a different picture than I'm hearing.
> No mics are without significant artifacts that can be heard in
> headphones with high amounts of amplification, but I don't think the
> source of the banding stems only from self noise or moisture induced
> problems with the mics. They're certainly not without wrinkles, but
> the "reach" of the Nt1A's, especially after I've done some eq to tone
> down the local resonance and the sound source is on axis with higher
> Hz content, can be shocking. I picked this night to work on because
> the action was thinner and it was very quiet. The mics are high
> ground too. I would not be surprised if the pickerel (we hope) was
> floating in the open water in the wetland 80 to 100 yards away. This
> qualifies as "distant" to me. Rob D.
I think the night was quiet enough. It is revealing some shortcomings of
the mics. If they are to be a "MKH replacement" then they have a very
high standard to meet and should be evaluated with every tool we can lay
our hands on. Right now, on the basis of this one recording I'd say they
are falling short of the standard set by the MKH. But that's highly
subject to revision as more careful field recordings are made. If the
sort of stuff I've found is normal for them, they have a problem, but
it's way too early to say that. Only more recording will sort out their
problems from natural stuff with more precision. I look forward to
hearing more nature recordings with them. The Sound Devices recorder
seems to be a good one for these tests.
As I always do, I primarily listened to these recordings at normal
comfortable listening levels. I don't believe in amplifying much above
that unless I've already got something at regular levels. This stuff is
there strongly at normal levels.
I mentioned headphones because I know how often those using speakers
only have problems picking everything out. I use both, but as I said for
serious picking apart the sound I use headphones.
Walt
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