A unidirectional microphone is sensitive to sounds from only one direction. The sound intensity for a particular frequency is plotted for angles radially from 0 to 360°.

I've just been given a Shure SM91 Unidirectional microphone complete with an in-line ILP-1 preamp :)
What's this type of mic used for in location recording? My first though was piano (cos it's a flat mic I suppose). Any hints, tips would be much appreciated.
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