You may need to also specify a length of time for which to record. e.g., rt:aud,rec,1500 to record for 1500ms from trial onset. Or rt:aud,rec,-1000 say to record for 1000ms beyond the moment the RT occurs. Otherwise if the trial continues automatically at the point of the RT, then there is nothing to record. Let me know if that doesn't cover it.

See also: www.empirisoft.com/directrt/help/directrt_samples_of12_voice_rts_.htm