A Mini Windjammer is simple lined fur cover to fit over the microphone directly or its foam gag. They are used on and off of camcorders to provide a cheap and effective protection against wind noise.
Standard & Special Mini Windjammers
Wind-noise is an inherent problem with all microphones. You can hear it as a low rumble, a loud fluttering or, if the noise overloads any part of the sound chain, serious distortion. Some microphone designs are more susceptible than others but it is always essential touse a wind-noise reduction system - a wind-gag - whenever there is any amount of wind or air movement.
With a light breeze a microphone wind-gag doesn't have a lot to do. The low-frequency wind-noise may be only 2 or 3dBs and so that's all the wind-noise reduction any gag can give you. However when the wind is blowing a gale and creating, perhaps, 30dB of noise you will need a device that can give you at least 30dB wind-noise reduction. A simple foam shield which can give 10-20dB reduction will work perfectly well if the leaves are barely moving on the trees but you need a Mini-Windjammer (which can give 30-40dB) if it's gusty - and if the branches are whipping about you'll be glad if it's a 30mm "long" fur version.
Of course, if you put anything over a microphone it will have some effect on the sound too. Rycote's designs minimise this as far as possible but the effect is inevitable. It is also constant - the slight reduction of high frequencies is there whether or not the wind blows. So there is a trade-off between how effective a wind-gag is and how much it sound is lost.
If the air is quite still and you are not moving don't cover your microphone at all. Enjoy the maximum clarity f sound. Above a wind speed of about 5mph - its very dependent upon your microphone - try a foam shield to keep the low frequency wind-noise away and cause very little loss of the high frequencies. Above about 10mph, and always when its gusty, since its those moments that cause the worst distortion, you will need a Mini-Windjammer. The 30mm "long" fur version gives the maximum reduction in wind-noise.