Electroencephalography and magnetoencephalography studies have shown that auditory cortical responses to self-produced speech are attenuated when compared with responses to tape-recorded speech, but that this attenuation disappears if auditory feedback is altered. These results suggest that auditory feedback during speaking is processed by comparing the feedback with its internal prediction. The present study used magnetoencephalography to investigate the precision of this matching process. Auditory responses to speech feedback were recorded under altered feedback conditions. During speech production, the M100 amplitude was maximally reduced to the participants' own unaltered voice feedback, relative to pitch-shifted and alien speech feedback. This suggests that the feedback comparison process may be very precise, allowing the auditory system to distinguish between internal and external sources of auditory information.