You are lucky that your stage fright is only right before and as you begin to speak. It is natural and normal for many speakers to feel some adrenaline symptoms right before a speech, including a trembling voice. They might feel a rapid or pounding heart, maybe some body tension, or perhaps a little cold or warm. First, it is important not to worry about those feelings. No one can see them. They don’t mean anything about how your speech will go. And in your case, as you say, you know they will go away once you get started.

However, here are a few suggestions that may help with your trembling voice, which may very well be evident to others:

1. Warm up your throat. A tense throat is more susceptible to producing a trembling voice once you begin to speak.

If the situation allows before you go up to speak, make a soft humming sound to open your throat and warm up your vocal cords, keeping your throat and vocal cords relaxed and ready to speak. Then a soothing open, deep “aaaahhhh” sound will move you even closer to staying relaxed when you are talking.

2. Translate sound into mental words. Immediately before you start speaking (with your throat open and relaxed), mentally think your speech’s first word or words.

Your throat and vocal cords will be ready for the sound to come through. You will be practically already speaking before you begin to speak to your audience. This way, you can “ramp up” to your first words rather than ask your brain and voice to suddenly “dive in.”

3. Stay loose. Remember, a little adrenaline is not the same as stage fright. Remembering this can counteract a trembling voice.

What you are experiencing may only be a bit of adrenaline, which can be a good thing. However, if you mislabel it as fear when it isn’t, it can add to your difficulties by making you tense up or clamp down trying to fight against those feelings. It is important to stay loose and not tense up against them but to allow them to move through you.

And for you specifically, it is essential to pay attention to relaxing your jaw, neck, shoulders, throat, and vocal cords.

4. Practice ahead. Let your mind get familiar with the words you intend to use.

Whether or not you have those opportunities before the event, practice them in private so that you can use them in the real situation. Practice relaxing and opening your neck and throat as you take an in-breath in preparation to say a word or make a sound that will move through your vocal cords and “ride” on the out-going air. As you breathe in this way, you will probably notice your chest and belly opening and relaxing simultaneously.

Practice this until this is automatic, and you can go to that position quickly. Then practice speaking a few words, or the first few words of your talk, allowing the sound to come up from your belly and chest through your relaxed and open vocal cords.

The more you practice this in private, the more quickly and automatically you will be able to relax and open your throat right before the first words of your actual speech. Then your voice will be smooth, and you can go confidently into your opening lines.

5. Channel your adrenaline. At the time of your presentation, harness your adrenaline to give clarity and power to your message, and any trembling voice will tend to disappear.

Picture a boxer preparing to go into the ring. He is feeling tremendous adrenaline at that moment. He starts dancing around, bouncing up and down, moving his neck and head back and forth to stay loose. He is giving the adrenaline something to do as it builds toward the moment he enters the ring. Then he directs all that adrenaline into his powerful entrance and the beginning of the fight.

You can use the same strategy. If you are out of sight of the audience right before you go on, it’s okay, actually helpful, to move around and stay loose as you direct your adrenaline toward the beginning of your speech. In fact, it can give you more positive energy and emotional conviction to put into your message.

P.S. Be sure of what you are going to say.

It also helps to know exactly what your opening lines are, so you are not dealing with any risk or uncertainty at that moment.

I hope this helps.