For the volume test, the louder the better right? And since multiple attacks on the one pitch is allowed would it count as cheating if you make one pitch significantly louder than the rest when you're building your device? Or do all the pitches have to be the same volume throughout
Yes, the louder the better. You can make one pitch significantly louder than the rest but it has to be part of the scale you play (which you conveniently get to choose). Also remember you can't make any adjustments after the pitch test (I don't think this really applies for your idea, but just in case).
Could you make a two-part device with an easily tunable component, like a xylophone, and a loud component, like a trumpet? If they're connected, you could have one person at the xylophone and the other at the trumpet. You wouldn't have to adjust anything.
Keep in mind it requires the pitch played for the volume test to be part of your scale, so that might derail your idea anyways.
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