throw (one's) voice
To cause one's voice to sound as if it were coming from a distant location or some other person or thing. He was able to throw his voice so well that he'd convince you he was right behind you. She threw her voice to make it sound like the large stuffed bear was talking.
Farlex Dictionary of Idioms. © 2015 Farlex, Inc, all rights reserved.
throw one's voice
to project one's voice so that it seems to be coming from some other place. The ventriloquist threw his voice. Jane can throw her voice, so I thought she was standing behind me.
McGraw-Hill Dictionary of American Idioms and Phrasal Verbs. © 2002 by The McGraw-Hill Companies, Inc.