The SEMA-1 aims to extend the capability of the camera system by adding a microphone input which is very important for videography. It allows, apart from the ME51S, different types of microphones with all their nice magnets to be used with an Olympus camera. Here it is attached to the OM-D:
It comes with an extension cable for the mic as well as a clip for when you want to use it clipped onto your shirt and tethered to the camera and moving it around.
Ultimately the best application for it would be a wireless solution so that the speaker need not be near the camera. While there is no manual volume control with the OMD it can be set to low, standard, and high recording volumes… I’ve settled on low with high wind reduction for now but Id probably need to tweak it for a setting with and one without the SEMA-1.
That’s it for now; I found this for 1,800Php, not really certain if this was overpriced, but that equates to like 45USD.