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MIDI LOOPER

*drum-in* and *hihat-in* are simple inputs connected to the corresponding instruments.
*drum-out* and *hihat-out* are simple outputs connected to the speakers which output drum or hi-hat sounds.
A bar of music is considered to be 4 time units in this puzzle. When a drum or hihat input is received, it should trigger the corresponding speaker in that time unit and also trigger it again in future bars of music.