QUOTE(kishgia @ Apr 20 2005, 11:38 AM)

Am I right to say that a strong embouchure, which needs some time to develop, is the key to reaching the higher registers? Are there any techniques or points to take note of when playing higher notes on the horn?
Yes, especially the mouth corners which will feel increasingly anchored against the teeth as you progress into the higher range. Imagining dimpling those corners against the lower teeth will help to keep the aperture open as you proceed upwards.
However, there are 3 other factors which are important in accessing those reluctant high notes:
1. Speed of air. The higher you play, the greater the velocity of air needed. Even if you are striving to stay open and not clamp your lips shut, the aperture does automatically become smaller as you ascend, so the increased air speed is necessary, not just to help with attaining those upper register notes but also to prevent loss of tone.
Facit: smaller aperture - faster air -- bigger aperture - slower air. Try thinking of a TGV going through a tunnnel.
2. Direction of air. The higher you blow, the further downward your air column will be aimed. These movements are very subtle so thinking it is enough -- doing it could be too much. When playing the lowest possible note on the horn, the air column will be aiming more or less straight ahead, whereas it will be streaming sharply downwards in the highest register. Somewhere in between those two poles is the right angle for any given note. Try this: buzz an easy middle register note while holding the palm of your hand (fingers pointing to the ceiling) about 10cm in front of your embouchure. Hold your hand so that the air stream is hitting the top of your middle finger. Now buzz higher (e.g. slow arpeggio or interval) and you will probably notice that the air is hitting your finger at a lower point the higher you play. Just being aware of this may help.
3. Shape of tongue. Some players, in trying to achieve what they think is a big tone, can fall into the trap of artificially pulling the tongue downwards as they go higher whereas it should, gently and in a very relaxed manner, arch higher the further up you play. Try whistling the opening of "The Blue Danube" or "Somewhere over the Rainbow" and you will distinctly feel this action. As you proceed into the high range it will feel as though there is a small funnel at the front of your mouth which gets progressively smaller the higher you go.
Psychology: Unfortunately we have to use words like "high" and "low" to communicate with each other but sadly, this can cause us to transfer them into "hard" and "easy." The more you can picture your range like a piano keyboard, all on the same level, the less difference you will feel in the various registers. That's what they are -- different, not harder or easier.
I hope some, or any of this helps.
hornblue