I have two configurations, one LG TV (2018 model 55SK9000PUA) connected to a Sonos Beam (Gen 2) using HDMI ARC and another LG TV (2019 model 43UM7300PUA) connected to a Sonos Ray using optical. When the TVs Digital Sound Out is set to Auto (Bitstream) it struggles with dialog sync; the severity varies between programming. If I set the Digital Sound Out to PCM there is no problem. The sync issue is more difficult with the Beam connected by HDMI ARC than the Ray connected by optical (why?). In the former case, setting the AV Sync Adjustment (on the TV) to 3 seems to provide pretty good correction.
The audio quality of PCM vs Bitstream in the Ray configuration does not seem to make any difference. Even when set to PCM the Ray (with Sonos One surround speakers) produces surround sound for relevant content. This seems to conflict with reports on the internet that PCM is only two channel; can someone clarity that in this context?
Bitstream in the Beam configuration produces a fuller sound than PCM. Unfortunately that is also the configuration that seems to struggle more with the dialog sync. As noted above, the TV’s AV Sync Adjustment at about 3 seems to provide good correction, although it isn’t perfectly consistent across all source content. Would the dialog sync be less of any issue on a newer model TV? Note I have tried the TV Dialog Sync setting for the Beam but it doesn’t seem to make as much difference as the setting on the TV.