Yamaha DTXpress/DTXplorer/DTXtreme

Most decent MIDI cables have a tiny circuit built-in.
The idea is that when connecting PCs and external
equipment, you can experience "ground loops" caused by
devices being grounding at different points. This can
affect the reference voltage used in MIDI data
transmission and can also damage equipment if ground
loop currents occur. The opto-isolator balances out
all these effects. Cheaper cables that don't have this
circuit may not work in every case and sometimes not
at all.
Hope this makes sense!

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