A speech analysis‐synthesis system was used to manipulate variance of fundamental frequency and a mechanical rate changer was used to manipulate speech rate. The synthesized and altered voices were tested for realism. Synthesized voices were mistaken for normal 50% to 58% of the time and rate‐changed voices were mistaken for normal 78% of the time. Additional studies were conducted to test the effects of these acoustical manipulations on the adjective ratings judges made of speakers. Variance of intonation was increased and decreased by 50% for eight speakers. There was a significant trend for increased intonation to cause voices to be rated more “benevolent” by judges and decreased intonation to cause them to be rated less “benevolent.” In two additional studies, rate was decreased and increased by varying amounts. Slowing the voices caused them to be rated less “competent.” Speeding the voices caused them to be rated less “benevolent.” Results were more consistent over speakers for rate manipulations than for intonation manipulations.