I have used a cheap jessops mic, a rode shotgun and a sennhieser radio mic with my gs400 and all worked very well. The gs400 has a mic and earphone socket which is unusual, often they are combined, there maybe a setting in the menu system for switching the jack socket from 1 to the other. This is certainly the case with the gs140 where the AV and headphones share a socket

Just a thought.

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Edius Pro 4 Broadcast, Edius DVX, ADVC300 -- PremPro 2.0, Matrox RT X100