Great idea Rob. Download both the new/updated Eb and Bb charts and the backing trqck.
Your son will play his part from the Eb chart and you’ll play your part from the Bb chart.
there’s no need to transpose anything, it’ll all work out as long as you’re reading from the updated charts and hplaying to the updtaed backing track.
the previous backing track will be in a different key so won’t work.
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