built in MIDI library ties up TX pin?

i've built midi in/out circuit pc900v optocoupler , lets me send midi arduino uno.
the basic midisimplesynth example sketch receives midi , plays correct frequency square wave out pin 10.

question: why echo midi data coming in rx out tx?
what if wanted use tx? ties can't use anymore , believe can't use serial monitor anymore either.

is there way stop this?

i'm answering own question. ended using
midi.turnthruoff();
now can use serial.println() without having data showing on serial monitor.
i realised need set serial monitor  31250.

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