The SES-A-V-SYNC is a L/R In-Out audio-video synchronization corrector. Another way to describe it is it is a compact device that corrects audio delays between audio and video. When distributing video over long distances through multiple devices like distribution amplifiers and set top boxes there can sometimes be a noticeable video processing delay which results in audio being played before the video. This also happens when the audio from sources is sent to audio amplifiers over analog lines while the video is send to the display over HDMI or digital lines. The SES-A-V-SYNC can be manually adjusted so the audio delay can be set from 0-300ms in set increments so you can perfectly synchronize your audio and video. The SES-A-V-SYNC is also sometimes referred to as a "Lip-Sync-Corrector".