Abstract: A system of controlling performance in an interactive voice response system includes a voice device driver, a voice segment stored in a file in a directory in a standard operating system format; a buffer for storing the voice segment prior to sending to the voice device driver and a plurality of voice channels for output of the voice segment. A sequence of voice blocks is requested to be sent to a buffer, the sequence being one of a plurality of sequences making up a voice segment. The number of voice blocks sent from the file to the buffer is determined. The play period of the sequence and the next underrun time when the sequence will finish playing based on the initiate request time and the play period are calculated. Also calculated is the margin period between the calculated next underrun time and the actual time after a further sequence of voice data blocks is sent to the buffer in response to a device driver request for a further sequence of voice data blocks.