TVs with 5.1 Passthrough from HDMI to SPDIF - Page 4

Probably the tv mfr. There are some that will pass 5.1 via HDMI but information is hard to find and confirm. I just run everything thru my avr and send just the video to the tv. Televison for us is OTA only so we just run optical out from the tv to the avr and get very nice, discrete 5.1 from the ATSC tuner.

Hi,

I am a new forum member after having consulted this forum for many years on various audio/video issues.

This particular thread has been very informative, as I have recently "upgraded" to a flat-panel HD television and blu-ray player, but continue to use an older (i.e. ca. year 2000) surround sound amplifier with a single co-axial and single optical SPDIF input.

I can CONFIRM that - out of the box - my new (2012 model) LG 47LM5800 television will not pass-through any surround sound signal coming in through an HDMI port. All surround sound signals (Dolby Digital AC3 / DTS) are either mixed down or stripped to PCM linear (not sure which).

HOWEVER, I can ALSO confirm that the service menu "hack" floating around on the internet for other LG televisions does allow the television to be set to passthrough a Dolby Digital surround sound signal from all HDMI inputs.

For instance, I have an LG blu-ray player hooked to my TV via an HDMI cord. The digital optical output of the TV is going to my surround sound amplifier. Prior to the service menu modification, the amplifier would only report it was receiving a linear PCM signal regardless of what type of audio track the blu-ray player was actually set to.

Once the service menu setting was changed to passthough Dolby Digital AC3, the Dolby Digital logo lights up on the amplifier's display whenever the blu-ray player is playing a disc with a 5.1 Dolby Digital audio track (i.e. a DVD or a blu-ray with non DD-HD track). Various speaker icons on the amplifier's display also light up depending on whether or not the Dolby Digital signal is 2.0, 2.1, 5.1 or whatever.

Use of the THX audio test found on a Lucasfilm Star Wars DVD confirms discreete DD5.1 audio is being passed through the TV to each speaker.

When I insert a regular audio CD into the blu-ray player, the DD logo disappears on my amplifier and it shows it's receiving linear PCM audio. Dolby Digital signals from my cable-company's PVR are also recognized by the amplifier according the multi-channel speaker information they contain.

The television will NOT pass-through DTS surround sound signals, however. When it receives a DTS singal the optical output is just mixed-down or stripped to become 2.0 linear PCM.

The LG TV also routes stereo analogue audio (from the component and composite inputs) through the digital output - which means audio from my Nintendo Wii console hooked directly to the TV gets routed to my amplifier (nice!). It also seems to preserve the Dolby Pro-Logic II surround signal being output from my Wii console - as I can hear seemingly discreete audio effects in the rear speakers. This would need more testing to confirm.

Editing the service menu was fairly easy. This link was helpful:
http://openlgtv.org.ru/wiki/index.php/Access_hidden_service_menus_/_modes

This PDF document - although not for my particular model, was similar enough to also be helpful:
http://*******.com/b8dvekz

You go into the service menu option "AC3 EDID D/L" and choose "START", then all HDMI and RGB inputs will change their status from "OK/(PCM)" to "OK/(AC3)". Exit the service menu, shut down and and turn the TV on again. That's it.

I was able to use a cheap RCA universal remote to enter service mode as described in the first link above.

NOW, I have one question: when the LG TV recieves a non Dolby Digital signal (i.e DTS or other multi channel digital), it passes it through as linear PCM. My question would be - is ANY surround information preserved in this linear PCM mixdown, or is it all stripped away to a stereo left/right 2.0 signal? I am HOPEFUL that the TV is at least smart enough to create a PCM stereo signal containing some surround information matrixed into a Dolby Pro-Logic signal. However, I realise it's probably - disappointingly - just stripping all the surround info out (or mixing it down to a simple Stereo left/right signal.

When my amplifier recieves one of these "mixed down" linear PCM signals from my TV, I do hear some activity from its back speakers. But I'm not sure if what's being sent from the TV is a true Dolby Pro-Logic signal or if, instead, the Dolby Pro-Logic II circuit in my amp is just trying to create a simulated surround sound signal from a basic two channel stereo signal (as this is what I've read Pro-Logic will attempt to do when it doesn't receive a true Pro-Logic matrixed signal).

Thanks.

If your particular model TV has the capability, you should see an option under "DOWNMIX" (or something like that) for either stereo or surround. How your receiver handles such a signal depends on many factors, including the brand, model, and year of manufacture. Many modern receivers can be set to automatically engage the Dolby Pro-Logic II circuit when they encounter a two-channel signal. Your receiver's manual should give you some idea of how it handles such signals.

The AC3 "hack" for some LG tv's has been around for awhile but it is a very dangerous thing to do. Depending on the firmware version, the hack may not always work and the ability to brick your tv with the wrong push of a button is very real. And if you mess up your tv, it is very difficult, if not impossible, to return it to factory. This is also something that is not covered under any warranty. There are features on the tv's that are not enabled depending on the model because a lot of times, the same boards are used in various models. However, with firmware updates, accessing those features from within the same model may change slightly due to the firmware differences, and what works on one, may not work on another. Service Menu modifications are not recommended.

I generally agree with your opinion. I would never touch any other setting in the service menu, but in this case it seems like a fairly straighforward and inoccuous change. Plus, it seems that by presseing the RESET option under the AC3 settings in the service menu, you can revert things to the original "PCM only" default.

Furthermore, it seems to work - my amplifier is receiving, via SPDIF, a DD5.1 signal passed through the TV from the blu-ray player's HDMI output.

I'm guessing that LG just disabled the DD5.1 passthrough due to HDMI liscencing / copyright restriction as mentioned earlier in this thread. I have no evidence to back that up though.

I've been using the pass-through audio for about four days now without any problem. I will, of course, report if there is any problem here on the forum.

It worked for you so that's good. All I'm saying is that we never know exactly what is in the different firmware versions or what an update will do to previous settings, and even something as obvious as Reset, might not do what you think it's going to do. I've seen people accidentally press the wrong button or have the remote stick (resulting in multiple "clicks") and instantly turn their tv into a very expensive bookend.

Another interesting observation. In checking exactly what forms of surround sound my LG 47LM5800 TV will pass through from its inputs to its optical output, I've found that any audio going into the TV with Dolby Pro Logic II encoded into it will pass through the TV unharmed and can correctly be decoded by the amplifier.

My test source was a video on YouTube which demonstrates Dolby Digital Pro Logic II surround sound by sending signals to each speaker in turn.

I first viewed this video through the YouTube app on my Nintendo Wii (which is plugged into my TV with analog RCA connections). I then viewed the same video through the YouTube app in my Blu-Ray player (which is hooked to the TV via HDMI cable).

The audio of both sources passed through the LG TV and was output via the TV's optical SPDIF to my JVC receiver (with the Pro Logic II decoder active on the receiver).

In both cases, each speaker of my surrond sound setup played a test sound at the appropriate time with little to no bleed or crosstalk between the speakers.

So, the TV does not "ruin" or strip out out a pro-logic encoded signal from digital or analogue signals fed into it.

It will, unfortunately, nicely kill a standard DTS surround sound signal - turning it into regualar 2.0 LPCM and outputting that via SPDIF.

Because of this, it's too bad very few (if any) of the audio tracks on blu-ray discs include a legacy Pro-Logic II surround sound matrix encoding within their front speaker channels. It's an older format, but it could be useful. In my case for instance, since the only type of digital surround sound signal my LG TV will pass through to my amp is Dolby Digital AC3 5.1, I am snookered if a blu-ray disc does not offer this type of audio track (i.e a DTS-MASTER disc). In this case, I must watch the movie using either PCM 2.0 mixdown done by the blu-ray player or the TV.

So I either end up with simple stereo audio (front right / left speakers only), or, by engaging the Pro-Logic II function on my receiver, I can turn this 2.0 signal into a "fake" surround sound, where the Pro-Logic circuit, not finding any real Pro-Logic encoding in the signal, uses other cues in the audio to create a simulated surround sound. If the studios still included a Pro Logic II signal in the two front speaker channels, I would at least get an older, but still useful form of "real" surround sound.

As a side note: From the YouTube audio tests, I was impressed with just how "discreet sounding" the old Dolby Pro Logic II surround sound could be. Despite the surround sound information being all mixed up within a stereo analog signal, it really works! I was also very surprised that Pro Logic II information could survive whatever audio compression scheme YouTube uses for its videos - but it did work well!

@ral-clan: why and how would the TV strip Prologic from matrixed 2 channel input...I think your player either defaults to downmixing discreete surround formats to prologic or you can select "downmix" by hand...

with my experience with LG TVs, it seems they indeed do not pass DTS through...granted, it can't decode DTS from its in-built media player, but why can't it pass through is a mystery...

As I think you've all figured out by now, Dolby Digital 5.1 (and DTS core) are not subject to copy forward restrictions any more than LPCM is. What I haven't seen discussed is that most TV's EDIDs will prevent a source from sending DTS and many will prevent sending Dolby Digital 5.1. That is why you see so few TVs that can pass either lossy multichannel format.

Dolby Digital is the easier of the two since ATSC requires decoding of it and therefore it is built into the decoding chipset. DTS is still rare in a TV. And, of course, many TVs are 2 channel only sets and that is what the source is told which means the source is only allowed to send 2 channel audio. So while HDMI permits it, the EDID in HDMI prevents it for many sets.
Edited by alk3997 - 1/18/13 at 7:37am

ral-clan - I believe Dolby Surround encoding will pass through a TV just fine. It is just a two channel signal that a TV has no reason to reject. Apply PLII processing in your AVR and you should get the same output you'd get if you attached the source directly to your receiver.

In post#97 above, you mention the presence of real ProLogic information in a signal vs the PLII decoder producing surround from basic stereo content on its own. I don't believe there is such a distinction. PLII encoding is not added data. It's a way of constructing the stereo signal so that a decoder can produce a specific surround output. If you tell your player to downmix a DTS track using surround encoding, it should produce the same output that you'd hear if the track had been put on the disc that way.

I suggest you use one of your AVR's digital inputs for the BD player in order to get DTS rather than the surround encoded stereo version output by the TV.
Edited by BIslander - 1/18/13 at 7:43am

Well, I was testing to see if ProLogic surround sound survived going through the A/D converter inside the TV - or being resampled from the blu-ray Player's HDMI connection to PCM.

I wish this were the case. If my TV could accept a DTS or AC3 surround sound signal and at least output a ProLogic II encoded PCM 2.0 signal, I could live with that. Alas, I'm pretty sure the LG TV just "scrunches" the surround sound signal being fed to it to a plain left/right stereo PCM signal.

While I agree that that is the best solution, it shouldn't have to be this way. The TV should pass through DTS and AC3 unaltered, but LG imposes an artificial "mixdown" barrier on the passing through of digital surround sound signals for some reason.

Since my AVR is an older one, with only one one optical input, I prefer feeding all my video sources to the TV and then having the optical out from the TV feed the single optical input on the AVR. That way I can get sound from all the devices hooked to my TV through my AVR (the cable box / game console / dvd player and blu ray player). If I hook the blu-ray player directly to the AVR, I am limited to TV's internal speakers for the other devices.

Get an optical switch. Or, if your AVR also has a coax input, use it for the BD player. However, if you'd rather live with matrixed 2 channel audio from BDs, then set your player to decode and output stereo with Surround Encoding. As you've already determined, the TV will pass that through just fine. It's not even possible for the TV to do the sort of scrunching you fear when the player sends a stereo signal.

This is not an LG issue. Most TVs work the same way. TVs are stereo devices. They are not audio processors and they'd cost more if that sort of functionality were added. An AVR is the place to handle audio processing.

But ral-can claims that his player is not capable of doing the mixdown...

I don't see that claim in his posts. Did I miss it somewhere? Plus, i don't recall ever seeing a player lacking that capability.

Hi, my Blu-Ray player is the LG BP620. A nice player, especially for the price, but I've been through every audio setting I can find in it and I don't see an option to mix down a digital surround source to a matrixed 2.0 LPCM.

There is a "PCM Multi-Ch" option, but from my understanding, this requires an HDMI connection to a (very modern) AV Receiver.

I currently have my Blu-Ray player set to "bitstream" which from what I understand, is a raw, untouched datastream straight to my TV's optical input.

The options under the Blu-Ray player's Audio menu are:

- PCM Stereo
- PCM Multi-Ch
- DTS Re-Encode
- BitStream

p29-30 of the manual. Set the output to PCM Stereo and DTS Neo:6 to Cinema or Music. Neo:6 is DTS' version of PLIIx.

Your TV has an optical input? That would be highly unusual. (I don't see an optical input listed in the technical specs, btw Just HDMI.) There's no point to digital audio inputs on TVs because they only play stereo and feeding them bitstreams that they can't handle, such as DTS, would produce no sound and create needless customer support headaches.

If you use an HDMI connection, then the handshake makes sure the source device sends audio the TV can handle. That's not possible with optical, which is a one way transmission. If you are actually using the HDMI input, the bitstream setting will be ignored. The TV will tell the player to decode and downmix to stereo. The player will use DTS Neo:6 when downmixing if you select the Cinema or Music options.)
Edited by BIslander - 1/19/13 at 11:17pm

"If you tell your player to downmix a DTS track using surround encoding, it should produce the same output that you'd hear if the track had been put on the disc that way.

I wish this were the case. If my TV could accept a DTS or AC3 surround sound signal and at least output a ProLogic II encoded PCM 2.0 signal, I could live with that. Alas, I'm pretty sure the LG TV just "scrunches" the surround sound signal being fed to it to a plain left/right stereo PCM signal."

Yes, I took it somewhat out from context...because he continues to talk about his TV striping the matrix encoding (which I can't believe is the case, he just didn't use the proper option in the player) and i thought he continued to talk about the player...DTS Neo does seem to be the right setting....

@ral-cal: you don't get prologic because the TV doesn't do the mixdown from the player's bitstream output, but may be doing it in the player via PCM 2-channel or, surely, via DTS:Neo setting should do the trick...If you selected Multi-channel PCM, then you certainly wouldn't get the mixdown of other channels into prologic...
Edited by mytbyte - 1/20/13 at 5:54am

The TV doesn't decode and downmix DTS tracks. Rather, it uses the HDMI handshake to tell the player to send a format the TV can handle. The player does the downmixing. If you set the player to use Surround Encoding, then you get the kind of downmix the OP is after. It's just a stereo signal as far as the TV is concerned. It plays fine as stereo. But, applying a matrix decoder such as PLII or DTS Neo:6 in a receiver will produce the additional channels.

So, this is a rather simple situation. Set the player to use Surround Encoding (DTS Neo:6 in this case). You can also set the player output to PCM stereo, although when using HDMI that is not necessary because the HDMI handshake will override the other player settings. Use a matrix decoder in the receiver.

However, I would still recommend bypassing all of this. You can get real DTS Surround by using an optical or digital coax connection from the player to the receiver. All it takes is a switch or an optical/coax converter, depending on the OP's AVR.

Thanks for all the input.

Yes, you're right. I mistakenly typed optical when I meant HDMI.

So, my setup is this:

Blu-Ray Player (LG BP620) ----HDMI----> Television (LG 47LW5800) ----SPDIF----> AVR (JVC RX-7520)

The JVC is an older AVR which only has a single optical input and a co-axial input.
It can decode the following surround sound formats: Dolby Digital (5.1 ACR), DTS, Dolby Pro-Logic II (no IIx)

Ah! Interesting! I had no idea my Blu-Ray player could do this...and in fact, I was ignorant of DTS:NEO until I read your post and did some research. Thanks for teaching me something new! But my AVR doesn't have a DTS:Neo decoding option. If I set it to Dolby Pro-Logic II, will it still be able to decode a DTS:Neo signal?

I tried what you suggested above. When the Blu-Ray player is set to "PCM Stereo", unfortunately the DTS:NEO 6 option is greyed out and cannot be turned on or off (I assume this means DTS Neo is disabled). Only when setting the Blu-Ray Player's audio to "PCM MultiChannel" is the DTS option available. So I chose PCM multichannel and switched DTS Neo to "ON". So now the audio output of my Blu-Ray player should contain a matrixed surround sound encoded signal embedded within the left and right front channels?

Another point of confusion: I thought that the "PCM Multichannel" audio setting on my blu-ray player (or any blu-ray player) could only be transferred over HDMI (as optical/co-axial connections don't have the bandwidth for 5.1 discreet digital audio channels). Isn't having a matrixed surround sound signal embedded into the audio of an already discreet digital channel transfer method kind of redundant? I mean, it would make sense if the DTS:Neo 6 option could be enabled when the Blu-Ray player is set to PCM Stereo. But why only allow the user to enable Neo when the Blu-Ray player is already set to PCM Multichannel?

This bit of information makes a whole lot of things make sense, now! So, despite whatever exotic audio setting my blu-ray player might be sent to, the TV will over-ride that and tell the player to "send me an audio format I can understand", right?

If that's the case, it would be helpful if there were some way for me to see which audio format my TV is requesting from the Blu-Ray player, and which type of datastream my blu-ray player is ACTUALLY sending to the TV. Is there a way?

Again, thanks for another new bit of knowledge. I'm new to this EDID thing.
Edited by ral-clan - 1/20/13 at 6:59pm

Okay, I just read the LG BP620 manual's section on DTS Neo:6. It says...

To me, it sounds like the manual is saying that when this setting is enabled, the blu-ray player will create a fake surround sound soundstage from a non-surround stereo source.

This isn't what I was suggesting at all in my messages above. I was just wondering (wishful thinking, really) if it was possible that a blu-ray player could take a 5.1 (or whatever) surround sound source (lets say a Dolby TRUE-HD source) from a movie, and do an "on the fly" encoding to a matrixed Dolby Pro-Logic II or DTS Nero:6 matrixed stereo signal so that people who had older AVRs, or TVs that would not pass a DTS signal through to the AVR, could still get some sort of surround sound (i.e. they would set their blu-ray player to output Linear PCM Stereo, the blu-ray player would do a real-time conversion of the TRUE-HD track to Stereo PCM containing matrixed surround sound encoding - either Pro-Logic II or DTS Neo:6 - which the AVR would decode (or re-assemble) into a soundstage that at least resembled the discreet channels of the original TRUE-HD source.

I realize the best solution is just to hook the darn blu-ray player directly to my old AVR, but I find it fun to think about other scenarios like the one above (it would also help in my situation as it would require less cabling and no switch boxes).

A lot of this has to do with how your TV and player function. It's odd that Neo:6 is greyed out when the output is set to stereo. Neo:6 includes rear channels for 7.1 systems. So, maybe your player can only do matrix encoding to expand 5.1 sources, not stereo. That would be unusual, but might be the case.

PLII should work even with Neo:6 encoding, although it may not be optimal. Remember, these are really just matrix processors that use the PCM itself to produce other channels. Identical sounds in L/R get sent to the center. Out of phase content gets used to generate the surrounds.

Since you have a second digital input on your AVR, why not simply use it to get genuine DTS?

The blu-ray player has SPIF output only.

The second digital input on my AVR is co-axial, and is currently being used by my DVD/HDD player/recorder. It's the only component in my setup that has a co-axial output connector, anyway. Might seem silly to keep it around when I have a blu-ray player and cable company PVR, but it's unlocked to play DVDs from other regions, will handle PAL DVDs and also the recording option is nice when I want to offload or archive material from my PVR. So it still has its uses.

Everything else in my setup uses optical. If I wanted to use my TV or blu-ray player with the co-axial input on my AVR, it would require a SPDIF to co-axial converter.

Yes. Optical-coax converters don't cost much at monoprice.com. it sounds like your DVD recorder is an occasional use box and you can simply swap cables when you need to use it.

There was an optical to co-axial converter on Amazon.ca for only $12.99 with good reviews (marked down from $27), so I ordered that.

http://www.amazon.ca/gp/product/B0002GV876/ref=oh_details_o01_s00_i00

I hope I don't experience any audio latency with the conversion.

My Samsung PN51E550 only sometimes passes Dolby Digital 5.1 via optical out on the TV. For my cable box, I had to do the "power down, hit menu button" trick to change HDMI audio to pass through for it to work. I haven't figured out Sony blue ray or Apple TV yet though (my TV only passes 2.0 PCM for those HDMI input sources).