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Blu-Ray Players - Optical and COAX out PCM Conversion HDCP - Downsample?

formdissolve

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The question: When converting HDCP material such as a Blu-Ray disc internally to PCM, are players required by HDCP standards to downsample 24-bit Dolby or DTS converted material to 16-bit before outputting PCM over the Optical or Coax outputs?

Why it matters: In the past, I've noticed truncated bit rate conversions to be harsh and edgy and would prefer the PCM conversion to be full 24-bit.

Note: I have a 2 channel setup and do not use an AVR or HDMI pre, etc.

This is a broad question that I've researched for awhile but have no conclusive answer. I did run across a document for a Sony UBP-X800 that I can't find anymore that stated something like "Due to HDCP protocols, copyright digital PCM data is converted to 16-bit when output over COAX output." (I am digging around to try to find that document). In the end, I'm fairly certain (but not sure) that my LG OLED converts signals to 16-bit 48kHz but I don't have a DAC that displays bit rate to verify.

History into the question: The main reason I ask is that my Panasonic DP-UB820 has an annoying audio sync issue when outputting the audio via the HDMI2 port or the Analog output (analog is the main reason I bought this player, other than Dolby Vision). This happens for all 4K discs, Blu-Ray, and DVD discs, but NOT Netflix or Amazon. I tried dozens of different options, settings, etc on the player, and tried them with 3 different TVs to no avail. This thread is not about diagnosing that issue.

The ONLY way I get perfect audio sync is when I output video and audio via HDMI 1. The audio through the TV speakers and through the TV's optical out is in perfect sync. On my Sony UBP-X800, I use the second HDMI port for PCM converted audio to an HDMI extractor, then from the extractor I output full range COAX to my DAC.

Most DACs that show sample rate AND bit rate are expensive. I wonder if I can hook my RME audio interface into it and see what the bit rate is in software..

I will be running some more tests this weekend to verify. Sorry for the long-winded post!
 
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Pluto

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OK, a few random thoughts on your predicament in no particular order. I'm fairly sure that the license agreement requires the digital output of HDCP content to be no higher than 16/48. This should be largely satisfactory (i.e. neither harsh nor edgy) provided the appropriate dither is being applied when downsampling to 16/48. AFAIK there is no direct way you can answer this question without detailed specifications of the devices used to unscramble & convert the data, and in-depth knowledge of the modes in which these devices are being used. However, you can create your own Blu-ray disc containing various test signals of known provenance, pass them through the process as far as you are able (obviously, you will not be able to replicate the copy protected environment) but I would take a bet that the 16/48 conversion will be applied nonetheless and subsequent inspection will reveal how well the sample rate conversion (if any) and bit reduction is being performed.

I can help you with analysis of files if you are able to capture the output. Take a look at this good page on the topic. Likewise, you may well find the products shown here to be of great interest. Have fun!
 
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formdissolve

formdissolve

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Thanks Pluto. I also am 99% sure the signal is 16/48, especially coming from the LG OLED optical out. I did try to play a 24-bit 88.2kHz file from my Sony through HDMI (which it supports) and all I got was hiss and aliasing noise from the TV optical out. That didn't surprise me, because I'd be more shocked if the TV supported anything over 48kHz. Ditto that for 24/96.

I used to own an Essence HDACC-II that I used for audio extracting/DAC but I ended up going a different direction and now am not looking to spend a ton of money.. but those HDFury options aren't terribly overpriced!

OK, a few random thoughts on your predicament in no particular order. I'm fairly sure that the license agreement requires the digital output of HDCP content to be no higher than 16/48. This should be largely satisfactory (i.e. neither harsh nor edgy) provided the appropriate dither is being applied when downsampling to 16/48. AFAIK there is no direct way you can answer this question without detailed specifications of the devices used to unscramble & convert the data, and in-depth knowledge of the modes in which these devices are being used. However, you can create your own Blu-ray disc containing various test signals of known provenance, pass them through the process as far as you are able (obviously, you will not be able to replicate the copy protected environment) but I would take a bet that the 16/48 conversion will be applied nonetheless and subsequent inspection will reveal how well the sample rate conversion (if any) and bit reduction is being performed.

I can help you with analysis of files if you are able to capture the output. Take a look at this good page on the topic. Likewise, you may well find the products shown here to be of great interest. Have fun!
 
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formdissolve

formdissolve

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I ended up digging into this a bit. I hooked up the optical out from the Panasonic to my RME BabyFace FS and used DigiCheck to verify that it is sending 16-bit for DRM HDCP audio from blu rays, and 24-bit for any non-drm flacs I played. Unfortunately, DigiCheck doesn't seem to show the actual sample rate of an incoming signal, so I wasn't able to confirm if it was sending the right sample rate. Unfortunately still, the audio is out of sync when using optical from the Panasonic, so I can't use that.

I then checked the optical out from my LG OLED and it was showing 18-bit which is strange for sure. Audio IS in sync, so I have to use this. I do notice some harshness from dithering effects but am forced to use this for now.

At this point, I'll probably just deal with the dithering effects. My other option is to sell both of my players and buy an Oppo 203 which is 1) Way too expensive on the used market, and 2) It won't have much support in the future (3 years or so I'm guessing they'll phase it out) in terms of firmware updates and any repair service if needed. That said, my 103 was perfect for 7 years + with no issues before I sold it, so I could give it a shot..

I could go the HDMI extractor route. The issue there is that the Sony UBP-X800 (that I use for region free blu ray playback) doesn't have an option to send stereo through HDMI and requires the receiver/extractor to have a stereo EDID. Some of the cheap switchers have that and force 24/48 max on stereo, but I've had issues with cheap ones sending clean video, especially HDR. The HD Fury ones look nice, but they can't convert multi-channel to stereo EDID since they rely on the source to do that.

Essence also has that HDMI extractor for $300 which is an option, but at that point I'd rather sell my players and go the Oppo route. Also, it only has 1 HDMI input, so that's not useful for the 2-3 I need.

I could also just get a home theater pre and use that, but they usually don't sound that great and are way too bulky for my setup.

The last option would be to get a Sony UBP-X800M2 region free, but my current X800 has issues with 4K discs and also with the M2 you have to MANUALLY turn on Dolby Vision to play a disc with DV. Turning it on forces the output of EVERYTHING to be DV, so an HDR only disc would look terrible. I guess it's not a huge deal since I only have about 6 DV discs, but in the future it would be crappy to constantly switch back and forth.. this seems like the easiest and cheapest route however.

Takeaways: I do have options, but all require spending a bunch of money all in the name of mitigating DRM dithering effects. Maybe my Panasonic player is broken in that it doesn't have proper audio sync from the analog out, the hdmi 2 port/the optical out when using PCM conversion, but it's beyond the return period and the warranty and don't want to deal with any of that. I'll just have to suck the teet of the DRM gods and deal with poor dithering from my TV for now. I miss the old Oppo standard blu-ray days when I had zero issues, but I guess 4K disc-based playback is still KIND of new (4 years), so I should be used to dealing with issues..
 
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Pluto

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Random thoughts....

do your TVs not have an option for adjusting audio sync with respect to the pictures?

I do notice some harshness from dithering effects
I am skeptical on this one. 99.999% of content contains sufficient noise to dither itself a hundred times over* so the usual caveats about making certain you are not deluding yourself, apply. If you really are experiencing added harshness, it is far more likely to be attributable to poor sample rate conversion than a bit-reduction issue.

It really does appear that you are getting yourself stuck up a gum tree of over-complication. I would stop, think, and devise a solution predicated on simplicity, not the addition of more and more kit to fiddle with the stream(s) in ways that may be somewhat uncertain. That's the world of HDMI DRM unfortunately.

FWIW my approach is never to use original DVD/Blu-ray directly but copy them (thereby stripping all DRM) and play them off a local server. By that method you know what's going in and what should be coming out.

*are you aware just how little noise is actually required to successfully dither a 16bit stream?
 
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formdissolve

formdissolve

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Pluto, I'm well aware of how OCD and mental this all sounds :rolleyes: - I'm very sensitive to lip-sync issues so I guess I notice it more than some others who have watched at my place. I'm going to be hosting monthly film screenings soon so I just want things to be as perfect as possible.

The first thing I did awhile ago was spend a few hours adjusting the TV's audio-sync delay and also the Panasonic's outside of that and it was never as right as it could be (and sometimes got worse as the movie went on), so I tend to avoid those.

As for the dithering/sample rate conversion, maybe it's something else I'm hearing on loud passages of a film and NOT actually any conversion (or just crappy soundtracks from older movies or something). However, I'm guessing the combination of converting a 7.1/5.1 DTS/Dolby soundtrack to PCM 16/48 stereo, then going through whatever the LG TV's processing is back to 2 channel 16-bit/48kHz is causing some oddities for my ears.

At this point, I'm just going to stick with the option with best audio-sync and deal with it.

(I was also going to start ripping some discs to a server once I get my NAS set up).

Random thoughts....

do your TVs not have an option for adjusting audio sync with respect to the pictures?


I am skeptical on this one. 99.999% of content contains sufficient noise to dither itself a hundred times over* so the usual caveats about making certain you are not deluding yourself, apply. If you really are experiencing added harshness, it is far more likely to be attributable to poor sample rate conversion than a bit-reduction issue.

FWIW my approach is never to use original DVD/Blu-ray directly but copy them (thereby stripping all DRM) and play them off a local server. By that method you know what's going in and what should be coming out.

*are you aware just how little noise is actually required to successfully dither a 16bit stream?
 

Pluto

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I'm well aware of how OCD and mental this all sounds
Compared to some around here, it's relatively rational!

I do know from a career spent looking at lip-sync (amongst other things :eek:) that it's a soul-destroying task insofar as the longer you look at it the harder it becomes to discern. Have you a decent test chart with matching sound to use? Secondly, for reasons I cannot fathom, audio sync does sometimes slip within a long film. This can generally be corrected by STOPping the playback (not PAUSE) and restarting. I do not understand the mechanism to explain why this happens but I suspect that there are variations in processing time that are not always correctly compensated (i.e. a pure black screen takes less time to process than complex action) and these variations eventually build-up to an objectionable level.

If your audio issues are predominantly around loud passages, I would be inclined to explore good old-fashioned overload (or overflow in the digital domain). Certainly the folding-down of a 5+.1 soundtrack to 2.0 is not a straightforward task before you even begin to think about DRM issues. FWIW dither artefacts tend to be more noticeable at very low levels than high. If you are able, prepare some audio at -40dB below normal and be prepared to crank it up on playback. This should reveal whether or not dither is the culprit. I'm inclined to think the issue lies within the fold-down from many tracks to 2.0. Perhaps you ought to consider a method of getting 7.1 (or whatever) out and providing yourself with the means (some sort of mixer) of controlling the fold-down.
 

Nick Laslett

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I do know from a career spent looking at lip-sync (amongst other things :eek:) that it's a soul-destroying task insofar as the longer you look at it the harder it becomes to discern. Have you a decent test chart with matching sound to use? .

I now use the slow-motion filming option on my iPhone to make delay adjustments. It seems to work.
 
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