It does not have much to do with testosterone. The fastest way is to do it is a hell lot of induced gag reflexes. This opens the complete Vocal chord from down below to neck. As in inserting two fingers deep in the throat to induce vomiting. You should do it when there is little or no food in stomach. You can drink water before doing this then the result would be even better. Within weeks Your voice pitch, depth will change. The more You do, the heavier your voice becomes. Question-- However, on the contrary being a singer I would like to retain my natural pitch which generally goes below with aging..  Also chatting Omkar in my young years had really helped my voice by then. Omkar cures many vani dosha. But it should be chanted correctly and it's better to learn it from experts. Answer -- Still induced gag reflex would work better than Omkar Chanting for all these.