When you watch TV, you are probably irritated when the picture and sound are out of sync but research has shown lip-sync error negatively impacts our perception of the characters too. Nothing could be worse in home cinema. Lip-sync error is usually caused by digital video processing delaying video allowing audio to arrive "before" the image. HD and 4K image size has increased the video processing delays aggravating the problem as have the flat screen technologies (LED, LCD, DLP etc.) common to all modern TV's and video projectors. Felston's DD740 digital audio delay can select between four s/pdif audio inputs (2 optical and 2 digital coax) and delay audio up to 680 ms in 1 ms steps (or 1/3 ms in fine mode) via its hand held remote while you focus on an undisturbed (no menus) image of lip movement and use its plus and minus buttons to zero in on perfect sync. In addition it performs optical/coax conversion and has two outputs (optical and coax digital) for input to your AV receiver or soundbar. In addition to the plus and minus buttons it includes a numeric pad for quick input of delay values and features 36 preset registers for instant recall and it also remembers the last delay setting on each input. These are features no AV receiver offers. Installation suggestion: Instead of taking digital audio (usually optical) out of your TV to the DD740 we recommend taking it directly from your sources (DVR, BluRay, etc.) and bypassing the TV. You will still use HDMI for video to the TV but some TV's delay the audio a fixed amount to offset their screen delay. That inherent video delay which can be used to offset the rare cases when audio arrives delayed won't be available if you allow the TV to add a delay. Even if your TV allows you to set its delay to zero there is still an advantage to taking audio directly to the DD740 since you will have Dolby Digital 5.1 available which in most cases a TV's HDMI inputs won't support.