The DDO may, for example, be provided by equipment which adheres to the SMPTE[3] Audio to Video Synchronization Standard.
This change can be accomplished by causing either the write or read address to jump forward or backward, however, this jump causes some audio samples to repeat or be lost resulting in an unwanted and annoying pop, click, gap, distortion and/or noise in the audio signal.
Using variable speed reading prevents pops, clicks, gaps, distortion and noise from being introduced into the audio, but does create unwanted and annoying pitch errors.
Audio synchronizers that use variable speed reading are generally preferred in professional applications.
Pitch errors in lower performance devices are uncompensated and kept to a level generally not perceived by the average viewer, by limiting the amount of change of reading speed.
Recent development in video processing devices permit those devices to sense when a large video delay change will need to be made beforehand and allow that change information to be communicated to the audio synchronizer.
Further developments permit handshaking between the video processing device and the audio synchronizer to control when the video delay change is made to optimize the timing of the tracking audio delay change thereby further reducing the risk of generating noticeable audio artifacts and at the same time reducing the risk of missynchronization due to rapid video delay changes.