There’s a lot of confusion about how different dynamic levels are produced on woodwind instruments. How do you think it’s done?
If you said something like “use more or less air,” you are on the right track, kind of. But how do you put more or less air into the instrument?
If you said something like “blow harder or softer,” you are asking for trouble. Adjusting volume by increasing and decreasing breath support causes all kinds of nasty problems, especially sluggish response, unfocused tone, and saggy pitch at softer dynamic levels.
So what method is left to adjust the volume of air entering the instrument, and the corresponding loudness or softness (weirdly, also called “volume”)? Surprise, it’s your embouchure. Take a look in the mirror at your flute aperture, or look at the opening in your oboe or bassoon reed, or the opening between the tip of your clarinet or saxophone reed and the tip of the mouthpiece. By manipulating the size of this opening, you can control the volume of air passing into the instrument, while keeping your breath support powerful and steady.
The opening isn’t large to begin with, so bear in mind that the adjustments needed are incredibly small. But your lip muscles are well-suited to very small, subtle, expressive movements—certainly more so than your larger breath support muscles.
If you are an advanced player, you are probably doing this already, maybe without realizing it. But if you are struggling with dynamics-related problems, like unstable pitch during crescendos and diminuendos, or the inability to maintain tone at pianissimo, you might want to reexamine your technique.
Try this: play a note in a comfortable range at an easy mezzo-forte, with powerful breath support. Without letting up on the breath support, apply just the slightest squeeze with your embouchure. (For me, the sensation is that my lips don’t really even move, they just firm up a little.) Gradually increase the squeeze—don’t forget to keep the support strong—and see what happens.
Try it again, this time starting with the lips squeezing, and see what happens as you allow the embouchure to become more and more relaxed. This maxes out when the reed is almost completely free to vibrate at its widest amplitude, or when the flute aperture gets too large to maintain focus in the tone. (At this point you may be able to get more volume by straining harder with your breath support muscles, but notice what happens to your pitch and/or tone!)
Like so much of woodwind playing, the real key here is breath support. If you remember to keep it steady, then creating dynamic changes from the embouchure is really quite intuitive and produces much better results.
Incidentally, this is why recorders, pennywhistles, and other “fipple” flutes really have only one dynamic level; the opening can’t be manipulated effectively because it is rigid. Blowing harder or softer does change the volume but at unacceptable cost to intonation. (This is probably a major reason the transverse flute essentially replaced the recorder in Western music—it could play with dynamic contrast.)