I've deleted the duplicate post in the DIY forum.
The M3 and NT3 are both
norminal cardioids. The M3 has a 0.5-inch capsule and built-in bass roll off while the NT3
has a 0.75-inch capsule and a flatter LF response. Other than that the two share broadly
I'm not clear on what you're trying to achieve, but for
outdoor location work a cardioid (or even a hypercardioid) is rarely adequate. Dynamic
mics are often perceived as being less sensitive to ambient sounds than electrets and
cardioids, but even that effect usually isn't sufficient for good separation in location
applications. Attenuation of sound sources 90 degrees off axis is only about 6dB with a
cardioid which isn't usually anything like enough.
The industry norm for this
kind of work is a short 'shotgun', or 'rifle' mic -- actually a hypercardioid with an
interference tube on the front. This provides far superior rejection of off-axis sound
sources for mid and high frequencies, and when used with a decent dose of high-pass
filtering, the hypercardioid's pattern and tail don't cuase too much of a problem at LF
However, the interference tube only works properly when the off-axis
sound is completely uncorrelated with the on-axis sound, so it works well outdoors or in
large open spaces, but not very well in smaller rooms.
standard go-to mic for location work is Sennheiser's MKH416 (or the newwer MKH60), but
Rode have a pretty good version of it called the NTG3 which is a lot more affordable.http://www.rodemic.com/mics/ntg-3
The other common approach
to minimise unwanted external noise is to use a close-miking technique, usually with omni
lavalier mics. The inverse square law of sound transmission means that the closer you can
get to the wanted sound, the much weaker the unwanted ambient sounds will be.
Technical Editor, Sound On Sound