During the Mythos Phase, if I draw the encounter named "Dissonant Voices",
Revelation – Put Dissonant Voices into play in your threat area.
You cannot play assets or events.
Forced – At the end of the round: Discard Dissonant Voices.
can I play "Ward of Protection" to cancel it?
Fast. Play when you draw a non-weakness treachery card.
Cancel that card’s revelation effect. Then, take 1 horror.
I am not at the Investigator Phase, so normally I can't play a card. But the card is labeled "Fast" so it doesn't cost an action, that's why I am asking.
It would be fine - that is exactly when Ward of Protection is meant to be used. It's further complicated by the fact that Ward of Protection is an Event, which Dissonant Voices prevents from being played. However, that would come into play only after the DV's Revelation Effect, which is what WoP is cancelling. Conclusion: Ward triumphs, Voices are silenced before they begin.