I was comparatively lucky. I've never had a particularly low voice, and I've always played around with it as a norm, so once I started working on it seriously I got results, though they were admittedly sporadic until this last week due to my brain being screwy with recall ability (I'd do perfect intonation and timbre, then immediately forget everything about how I'd done it; note that this is different from not knowing how I did it in the first place).