used for 2.5mm TRRS balanced output -professional or portable digital audio player such as FiiO, Astell&Kern products, and 4.4mm TRRRS balanced Cables
used for 4.4mm TRRRS balanced output - professional or portable digital audio player such as Sony , and 4.4mm TRRRS balanced Cables
used for 3.5mm TRS Unbalanced output - cellphones or most of portable digital audio players, and 4.4mm, and TRRRS balanced Cables