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Re: Wind sensitivity

Subject: Re: Wind sensitivity
From: "Mike Rooke" picnet2
Date: Mon Sep 26, 2011 12:54 pm ((PDT))
Thanks David, I use a pair of Rode Blimps normally but will switch to Rycote 
after talking with Rycote UK. 

Out of interest, heres the dynamics compared to Shure WL183's (MX391 boundary 
mics) for Environmental noise, I was hoping the recorder recording the dynamics 
would last a bit longer for the dawn chrous but it wasn't the case. The Korg 
MR2's 6 hour limit is rather annoying in this regard. Hence most of the 
comparison is noise followed by the bird calls at the end captured with the D50 
/ Shure capsules. The array configurations are different, parallel dynamics 
facing forwards vs boundary omni's. The amount of traffic din increases as the 
daily grind starts.


--- In  "Avocet" <> wrote:
> > I've seen the occasional reference here to some microphones being 
> > more sensitive to wind than others, and assumed it was because of 
> > something about their shape making them catch the wind more. But 
> > surely once they're inside some sort of wind cover, they're all 
> > equal in that regard?
> Mike,
> It is the outside shape of a blimp or sock or whatever windgag which 
> creats most wind turbulence. A false fur surface produces much less 
> turbulence and at a lower frequency than a smooth surface such as 
> stretched cloth or foam.
> That's only a partial solution as the mic is still going to be hit by 
> turbulence from the mic mount, stand, hand or the body of the person 
> holding it. The killer frequencies are around 1 Hz to 20Hz which don't 
> sound as audio, but these freqencies can easily modulate or chop up a 
> recording making it unuseable. You can't filter this out later. You 
> won't find anything about sub-audio in the mic specs.
> Any directional mic has an omni sound pressure function combined with
> a fig-8 velocity function. It is the sensitivity to the velocity of 
> the sound which makes them highly susceptable to both air and mic 
> movement. It doesn't matter what gizmos are inside the mic body, there 
> is still a velocity component to its sensitivity. If that velocity 
> component has a sub-audio frequency response it can be a serious 
> problem.
> Any mic input stage needs a high pass filter, and for field recording 
> it is useful to switch in a "bass cut" response. This is typically 6dB 
> per octave and a bass cut is well worth using to avoid any input stage 
> overloading. The bass can be equallised back in on replay with no 
> quality loss.
> Putting an inner puffgag or soft shield inside a blimp where there is 
> no wind has the effect of adding an acoustic HPF which raises the 
> overload point of the mic itself. However, if you do frequency 
> response tests it will make a difference to the mic axial and and 
> directional responses. However, that's better than an oveload.
> A well designed "yeti" sock over a blimp will act as a HPF/bass cut as 
> well as streamlining the blimp as above. However while this may 
> prevent the mic itself overloading, and the bigger the blimp the 
> better, the unquoted response region around 1 to 20KHz may well have 
> high sensitivities in some directions. You won't find this on any 
> polar diagram, neither will you find an off-axis frequency response 
> which is often very different from the axial response.
> To sum up, use the biggest diameter blimp and a strong bass cut on the 
> input to avoid wind overloads. You should still hear wind on the 
> surroundings like grass, shrubs or trees or yourself, or even off the 
> ground, and as long as these dot overload your recording at low 
> frequencies, they are part of the environment you are recording.
> David
> David Brinicombe
> North Devon, UK
> Cogito cogito ergo cogito sum - Ambrose Bierce

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