Problems with LG Toslink Output

[TurtlePaul]

I posted in the thread about in-room measurements and it is noted that when I pass sound through my LG TV (technically a monitor) 48GQ900-B, the sound gets all messed up. Rather than just look at the in-room measurements I decided to measure from the DAC output straight into my PC to see what is happening electronically.

Here is the frequency response of my MiniDSP 2x4 HD with no filters send via USB input (in red) and the Toslink from the monitor (in green).

I tried to make sure this wasn't the MiniDSP (red), so I also tested with a JDS Labs Atom+ DAC (blue).

The frequency response characteristics do not depend on volume level, so it isn't some sort of limiter. It almost looks like a weird de-emphasis filter, but who has pre-emphasis CDs anymore and why would the DACs this my PC needs de-emphasis?

I was expecting the roll-off to be a 6 db/octave filter, but now I see that it is some strange modulating roll-off response. Anyone have thoughts on what this could be? I have emailed LG support.

 

[Doenerkunde]

The frequency response somehow reminds me of cinematic target curves.

X Cinema target curve:

Dolby Atmos Music target curve:

Interesting topic btw. I have given up on my Sony TVs optical out for musical enjoyment. Sounds thin and lifeless, like all "attack" is sucked out. Someday I might get a DAC with HDMI because of it.

 

[Chazz6]

So that LG monitor has a terrible Toslink output, while its USB output is fine. And then we learn that Sony TV Toslink outputs sound terrible.

Don't blame Toslink in general. I have a device (Denon LinkHS2) that receives digital audio over wifi and sends it out via coax or Toslink. Coax picks up a hum; Toslink is clean.

 

[TurtlePaul]

So that LG monitor has a terrible Toslink output, while its USB output is fine. And then we learn that Sony TV Toslink outputs sound terrible.

Don't blame Toslink in general. I have a device (Denon LinkHS2) that receives digital audio over wifi and sends it out via coax or Toslink. Coax picks up a hum; Toslink is clean.

To be clear, the TV does not have USB output - my DAC has USB and Toslink input and the USB is connected directly to the PC while the Toslink detours through the monitor via Displayport from the PC.

I am just flabbergasted that I can't get a PC to send the monitor a 2-channel 24/96 input and get the same 24/96 bit output.

 

[Chazz6]

I am just flabbergasted that I can't get a PC to send the monitor a 2-channel 24/96 input and get the same 24/96 bit output.

We who inflate ourselves as serious listeners depend on our "serious" audio equipment. We never expect good audio from a home theater box, nor when we got to an old-fashioned movie theater.

 

[TurtlePaul]

To the mods: sorry for posting this in the speaker review subforum. I meant to post in General Audio Discussion.

So I have tested the LG OLED Monitor (which is essentially a TV) with two separate Displayport sources as inputs and two separate DACs as outputs. I also tested my PC Displayport into an ASUS VG27AQL1A monitor which has an analog sound output. The ASUS measured +/- 0.2 dB 20 hz-20 khz. Next I will test the faulty LG monitor's analog headphone out. I wonder if the weird filter response was meant to be only applied to the physical speakers (that likely break-up at those higher frequencies)?

 

[TurtlePaul]

So I have learned a bunch more things:

- I think that the monitor's optical output may be using a filter which was intended to fix the TV internal speakers.

- The monitors headphone output supports DTS Headphone X which has funky headphone filters - DTS Headphone X is weird because it seems to simulate SBIR and floor bounce defects but I am sure it also has crossfeed.

- When turning off the DTS Headphone filters I get a clean electronic response on the headphone out, suggesting that the input from the Displayport is clean and not being filtered by the PC (the yellow line)

- The response is weird from the Toslink connection regardless if I test at 24/96 or 16/48, so it isn't an issue of data rate overloading the Toslink (note I made volume changes on the MiniDSP between the measurements, the digital level didn't change)

- The monitors internal speakers sound really really bad (response omited, but has a huge response hole)