LG TV optical PCM output distortion (clipping, fuzzy...) to soundbar

Adam Bodorkos

Aug 3, 2015
Hi All,

I'm experiencing a very strange issue with my HDTV (LG 42LB5610) and new soundbar (LG LAS350B). Okay, first the issue itself, and then the circumstances how it shows up:

The issue:
Audio output via optical cable from TV sounds... incorrect. I don't know how to describe it best -- "harsh" treble, "clipping" high frequencies, distortion mostly during spoken S, T, F sounds -- I mean it sounds mostly OK, but the highs are definitely wrong and fuzzy. The audio doesn't cut out abrubtly though (like many people post on different forums), this issue is constant.

The "when and how":
(I think) I have narrowed it down to the following scenario:
Soundbar receives PCM 2/0-0 signal from the TV.

Interestingly, when I plug the optical cable into a Playstation 4 and directly into the soundbar, it always sounds perfect, no matter which audio output format I choose on the PS4 (Linear PCM, DTS Bitstream or Dolby Bitstream). Also, TV channels that have Dolby audio -- if the TV is set to "Auto" audio output, Dolby is used and all is fine, HOWEVER if I change to PCM output, the sound is wrong again... Just like on non-Dolby channels where PCM is output by default.

BUT... this behavior doesn't seem to be 100% consisent. I've been testing all kinds of input-output configurations and on a few occasions, changing back-and-forth, doing I-don't-know-what fixed the PCM issue!!?! I swear I could change to all those inputs that were output wrong before, and they would sound correct. I even noted down the actual settings, but after powering off the TV and soundbar, the next day everything is fuzzy again.
I know it sounds like I haven't tested thoroughly enough, but I have, I just don't know what else to do. There doesn't seem to be a consistent way of avoiding the problem with PCM output.

Has anybody heard of an issue like this? I've tried searching for firmware updates, forum topics about faulty PCM-downmixing and such, without success.

  • Is there a place where I could find known and/or fixed LG TV bugs or customer complaints?
    Has anybody ever heard about issues with digital PCM output?!
    Am I correct that it must be the TV, since the PS4 PCM output is perfect?
It would be great if someone could figure out what is going on! Thank you!

Adam Bodorkos

Aug 3, 2015
UPDATE: I've found an interesting way to temporarily FIX the sound coming from the TV. However, after turning it off and on again, it reverts to being "distorted".

0) Initial settings are: PS4 - Linear PCM output, TV - PCM, and the sound is crackling
1) I change PS4 to output Dolby Bitstream, sound is still bad (since TV converts it and outputs PCM)
2) I change TV output to Auto (basically Dolby in this case), which fixes the sound (Soundbar INFO now shows Dolby as input
3) I change PS4 to output Linear PCM again - and surprisingly, the sound is still good!! (TV now outputs PCM just like at 0) and Soundbar INFO shows PCM)
4) I change TV output back to PCM, and sound is still correct... Note: the settings are exactly the same as they were initially....

At this points, if I switch to non-Dolby channels or USB playback (which both had the crackling) - sound is good as well!

Now if I turn off the TV, crackling is back... If I only turn off the Soundbar, it will stay correct.


Aug 21, 2015
I have a similar but different issue. I have an LG 55UB820V TV which I input from a Pioneer VSX-323 amplifier (from Raspberry Pi/PS4/PS3/ BT Vision), and also link back some audio using a fiber-optic lead for using the TV's on board Spotify and YouTube etc players.

What I have noticed is the sound going back from the TV to the amp via the fiber-optic lead is awful (like you mentioned above), it sounds like it's distorting at any volume. I don't know how to fix this and it's driving me up the wall. When selecting the Optical output in the TV's settings - it offers no options to adjust signal output. Also my amplifier has no options. This distortion does strike me as weird as the signal is digital.
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