Has anyone made a search?
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This topic was covered and solved in the distant past, long before the demand for iThings glutted the accessory market.
I remember posts containing pictures and links of a Y-cord consisting of a 3.5mm, 4 conductor male plug on one end branching out to two, 2 conductor female jacks on the other end. The wiring was correct in this adapter to enabled the use of any standard headset/mic (these headsets generally have two plugs - one for the mic and one for the earphones.)
Try to use a mic that advertises the elimination of background noise. I do suspect, however, that part of the loud background problem is an aggressive compressor in the Tablet's mic circuitry.