The description for the Disturbing Voice talent states "... gains +10 bonus to all Intimidate or Interrogation tests when he employs this talent..."

Does this mean that the Explorer can choose when they want to activate this power or it is assumed to be always activate, a partmanent change in the character?

I think "employ" means that after you buy it, it is a permanent change.

Given the other part of the description, I'm leaning towards an always-on effect as well. I'd allow a Disguise check to try and muffle the effect though.

Macharias the Mendicant said:

In Dark Heresy: Ascension there is a paragon talent called "Voice of the Omnissiah" which replaces Disturbing Voice and a few other talents. It allows the effect of Disturbing Voice to be turned on and off. It is a Dark Heresy book though and it would have to be an elite advance if available at all.

Svarte Hanske said:

I belive "employ" in this case indicates that you are actively using the talent. While the changes to the vocal systems are indeed permanent, the effect can be turned on or off. Or, if we want a real, official answer, ask Sam.

-=Brother Praetus=-

But why should there be a negative effect at all if one can just turn it on and off?

Svarte Hanske said:

Because the whole of the description was not included and I did not bother to double check it prior to my post. It's still conceivable that it can be turned off; but given the rest of the write I would have to revise my above post on the matter.

I have to remember to stick to my personal rule of no posting responses when sleep deprived.

-=Brother Praetus=-

As much as I might want to be able to "switch it off" when it would be inconvenent, I think I'm leaning towards a permanent effect/change with the Explorer having maybe some minimal control over how obvious the Disturbing Voice is. I suppose it is difficult to rationalize the inclusion of a negative impact for a power you can just switch off...

I suppose that when you are not "employing" the full power of your Disturbing Voice, you might be able to try to conceal or mask it. (I think a Disguise test is a good call for that. I'll run it by my GM.) Then again, the negative effects are not that severe. They seem to suggest that when interacting with most people (in a non-menacing manner), there is no penalty at all. Only when interacting with those who are predisposed to be frightened by the unusual voice does the Explorer suffer penalties. (My understanding of this is that a character with Disturbing Voice speaking to your average Imperial Guadsman or Arbites enforcer would not suffer any penalties at all.)

So, I guess you can't switch it off, but neither does it apply in all circumstances? (seems about right to me, actually.)