Blow soft warm air…same thing i found on soprano and it should sound sweet not shrill.( the soprano)
Each one though has its own chalenge. So for me soprano was to make it sound mellow amd sweet instead of shrill. They take less blowing tha. The bigger recorders I found. So the tenor has the difficulty (for me) to hold it without getting tired, to sound good of course and to position fingers rightly. That’s the mature of the beast. Alto is the happy medium I’d say not to small or shrill and Mot too large BUT…The first note is an f not a C …so that changes quite a lot= another chalenge!
Hole spacing is nesecarry obviously for the tuning to be right. Perhaps you should look into the ones with button?
But anyway you do get used to it.
For low C make sure all holes are covered properly and use soft warm air ( like trying to steam up a window.)
Kind regards
Martin
All music is an inspired creation.
All creation is made and held by sound and music.
It all has one source and with our music we merely mirror his beauty.
Martin