I am an intermediate player of both trumpet and sax - something like 5th grade in the ABRSM system. I played trumpet first (20 years off and on) and sax later (10 years off an on). I have tended to play one or the other at any one time but played the 'off' instrument occasionally enough to double if necessary with a couple of weeks practice.
When I first started playing sax, I noticed that I would drop to trumpet fingering (but in other hand) occasionally when sight reading under pressure in the Bb to C# range where the fingerings sort of overlap:
trumpet Bb = 1 = sax B
trumpet B = 2 = sax C
trumpet C = open = sax C#
That corrected itself as I played more sax and less trumpet. However, for the first time, I am regularly playing both instruments. And I am now having the opposite problem of my brain doing the sax fingering when I am playing trumpet, again particularly when sight reading.
Does anyone who doubles on these have any suggestions on how to fix this? Obviously I need to practice both instruments.
But I am wondering if people who play both do their practice separately or together. That is, would I be better off just playing one instrument for a week then doing the other the following week? Or should I try and play both instruments fairly constantly in the hope that my brain will eventually use other cues to attach the correct fingering to each instrument.
Also, any suggestions on particular drills I could use? For example, are scales or pieces of music better for fixing this?