My oboe students frequently have this problem:
|These notes don’t respond well||These notes are sharp and thin-sounding|
(Okay, sometimes I also have this problem.)
The solution, in most cases, is quite simple.
Step 1: Use the correct voicing. For oboe it should be low and open, like blowing very warm air. This is usually the result:
|These notes respond beautifully||These notes are flat and tubby-sounding|
Step 2: Use powerful abdominal breath support. Voilà:
|These notes respond beautifully||These notes are in tune and full-sounding|
I find that once voicing and breath support are balanced against each other, a good oboe with a good reed is one of the easiest woodwinds to play in tune, and responds easily in all registers.
This is, generally speaking, true of all of the woodwinds: solid breath support plus a stable voicing appropriate to the instrument are the recipe for reliable, in-tune notes from low to high.