In a recent blog post, Nick Morgan advises to pitch your voice lower when presenting. When we are nervous, we tighten our vocal chords, which results in a high "shrieky" voice that radiates lack of confidence.
I see many people do this even in smaller meetings, and especially some women are dropping their voice pitch dramatically to come across stronger in a male/testosterone-loaded world. In many cases this sounds very artificial.
Part of the exercise of lowering your voice is probably not related to your voice at all, it gives you something to focus on that simply calms you down. When you are in your mental low voice mode, you feel more confident.
I would treat lowering your pitch as a last resort, and hopefully other stress reduction techniques (including having tremendous confidence in your story) enable you to keep your own natural voice.
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