It's normal for a soundbar to go into standby when it doesn't receive an input but it usually has a pretty long delay.
The optical audio output is digital data so it isn't actually lower during quiet passages. It is always on when the TV is on except maybe when you change channels and inputs.
You could try changing the audio output type in the TV menu but I suspect that won't help.
If the JBL is under warranty I would have it taken care of since it could get worse.
Thank you for your quick response!!
It is clear to me that digital output doesn't distinquish between quiet or loud so it looks that it is a problem with the soundbar. I will have it checked, but first of all i will try another audio output mode of the TV (like you suggested).
Meanwhile I have presented the case to JBL support and they will get back to me.
You were right, optical output cannot be changed in volume. I also tried to change the audio output but that did not give a better result.
After contacting JBL support today, they advised me to use the HDMI / ARC option (so buying the supporting HDMI 1.4 cable) because this should avoid the problem of the "unwanted mute". Lets see what happens after the arrival the cable... to be continued....
The final report on the LG - JBL issue: the new HDMI 1.4. has arrived and was installed (between LG TV ARC port and JBL soundbar ARC port). NOTHING happened, silence was the end result.
I called LG support: conclusion of the 'expert' was that ther is an incompatibility problem between LG and JBL. So much for the "standard" HDMI ARC....
According to the 'expert' buying a LG Soundbar would solve the problem; yeah, SURE.. I believe him but that ain't going to happen!! Just spend a little fortune on the (in my opinion) excellent JBL soundbar.
Another call with JBL support: Some older TV's (of different brands) just don't seem to work according to the ARC standard. I must have had bad luck in this case.
Advise: either try to deal with the sudden unwanted short shutdown of the JBL (using the optical connection) and wait until its time for a new TV (with working ARC) OR.. try to simulate the problem with another TV (with optical connection) and - in case the same shutdown problem occurs - return the JBL soundbar (under guarantee) to be checked and repaired.
Generally speaking I am rather disappointed with the way manufacturers seem to interpret the "ARC standard"...
HDMI, in general, has been a royal pain. eARC which is forthcoming is supposed to be better.
There are standards but they are often not met. Even the cable can make a difference although mostly it's the longer lengths that can drive you crazy.
Check out the soundbar with another optical source (TV, computer, Disc player, or cable box). My guess is that the soundbar is faulty.