How to disguise a voice for broadcast

A client requires that an interviewee’s voice be disguised in post production for a radio podcast.

What effects do you recommend?

Is it possible to make the pitch effect monotone by removing modulation?
Does time stretch affect pitch?

I would recommend using a combination of pitch and EQ. Don’t go too far though as even though you don’t want the voice recognisable you’ll still want the audio to be decipherable.

I would recommend pitching it down rather than up as up would end up making it seem comedy rather than serious. Pitch it down a little at a time until you’re happy then you can play with EQ to disguise it further but again remember it has to sound audible still even if not recognisable so again don’t go too far.

I would use pitch shifter effect so you get a consistent sound.

Time stretch will also affect the pitch becoming higher of lower depending on whether you shorten or lengthen the duration.

Great suggestions @markdenholm.

Pitch shifting down can always be reversed so bear that in mind if disguising of the voice is critical. iZotope Vocalsynth 2 will more than mask a voice but, like Mark mentions, don’t go too far with the effects!