Posted Fri May 7, 2010 at 11:30 AM PDT by Joshua Zyber
Editor's Note: Each Friday, High-Def Digest's own HD Advisor will answer a new round of questions from our readers. If you have home theater questions you need answered, send an email to [email protected]
Answers by Joshua Zyber
HD Audio Confusion Revisited
Q: Okay, you now got me REALLY confused about audio codecs. My understanding was that the "core" audio on DTS-HD Master Audio and the Dolby Digital fallback track for Dolby TrueHD were there if BOTH the following circumstances were met: The player has no internal audio decoding AND the receiver is incompatable with the HD formats.
Maybe it's a placebo effect on me, but with my setup, I have a PS3 hooked up with Toslink to my receiver, and the PS3 set to bitstream the audio. I am pretty sure that there is a noticeable difference between the HD audio and the lossy ones when both are encoded on the same disc. (Although some of this may be due to loudness, there definitely seems to be more bass and clarity in the lower and upper ranges). My understanding based on what I have read and in your previous articles is that audio and video have to go through a DAC somewhere in the chain, and the PS3 has internal audio decoding. So my understanding has always been that a PS3 decoding the HD audio and passing it in Dolby Digital or DTS over Toslink to my receiver should produce the same sound as passing it over HDMI to a newer receiver and letting the receiver do the decoding. In the end, it has to be converted to analogue anyways to be heard. Last I checked, no one is running fiber from their receivers to their speakers, nor do our ears understand 1s and 0s.
However, your last article where you tried to explain HD audio, it made it sound like I am not getting HD audio at all, but the PS3 automatically plays either Dolby Digital or DTS core. So, to sum up, here is my previous understanding:
Player with No internal audio decoding + No HD audio receiver = Lossy audio.
Player with No internal audio decoding + HD audio receiver connected via HDMI = HD audio.
Player with Internal Audio decoding + No HD audio receiver = HD Audio.
Player with Internal Audio decoding + HD audio receiver connected via Toslink, coax, HDMI, or analogue = HD audio.
However, based on your last article, it sounds like the following is true:
Any player + HD Audio receiver connected via HDMI = HD Audio.
Any player + any other receiver setup = Lossy Audio.
Could you please clear this up once and for all?
A: To start, I recommend that you read through my old Blu-ray Audio Explained article. Take a look at that and see if it clears up some of your confusion. To address your specific question, if you have a Toslink cable connected from your PS3 to your receiver, you are not getting HD audio. (At least, not in 5.1.) If you've set the PS3 to "bitstream," the player will fall back to the DTS "core" or the backup Dolby Digital track on the disc. A Toslink cable simply cannot transmit the native bitstreams for any of the HD audio codecs.
If you set the PS3 to decode the audio formats to PCM internally, the most a Toslink cable can carry is 2 channels of PCM. In that case, you'll get a lossless quality, but downmixed to 2.0 format.
The following are the only ways to get 5.1 HD audio in full lossless quality:
To bitstream the soundtrack from player to receiver, you must have a Blu-ray player that offers HD audio bitstreaming. (The PS3 Slim has this function, but the original PS3 does not.) This must be connected by HDMI to a receiver that has the ability to decode those HD audio formats (Dolby TrueHD or DTS-HD Master Audio). There are no other connection options for this.
To internally decode the HD audio at the player, you must first have a player with the necessary HD audio decoders. (All versions of the PS3 can do this.) The player must be connected either by HDMI or by multi-channel analog. In this case, it is not necessary for the receiver to have HD audio decoders. But it must have either HDMI or multi-channel analog inputs, obviously.
You will never get 5.1 HD audio over a Toslink cable. It can't be done. The player will always fall back to the lossy core or backup track. Any difference you may believe you've heard can be chalked up to either a volume difference and/or placebo effect. Unfortunately, the technology just isn't there to deliver the full lossless signal over that cable type.
Digital-to-Analog conversion is indeed a very important part of your final audio quality. This step always takes place after the decoding is done. These are separate processes. If you use any type of digital audio cable (be it Toslink or HDMI), you default to using the DAC components in your receiver, regardless of where you perform the decoding. If you used multi-channel analog connections, you'd be relying on the DACs in the Blu-ray player. Since the PS3 doesn't have multi-channel analog outputs, you'll always be using the receiver's DACs.
Those DACs, while crucial, remain at the mercy of the decoded signal fed to them. They can't turn a lossy signal into lossless quality.
To use your chart:
Player with No internal audio decoding + No HD audio receiver = Lossy audio. - Correct.
Player with No internal audio decoding + HD audio receiver connected via HDMI = HD audio. - Only true if the player offers HD audio bitstreaming. In most cases, this goes hand-in-hand with HD audio decoding. There are few players that offer the HD audio bitstream option without also being able to decode.
Player with Internal Audio decoding + No HD audio receiver = HD Audio. - Only if connected by HDMI or multi-channel analog.
Player with Internal Audio decoding + HD audio receiver connected via Toslink, coax, HDMI, or analogue = HD audio. - Incorrect. This answer is identical to the one above. If decoding the audio within the Blu-ray player, you must be connected by HDMI or multi-channel analog.
With all that said, do you now wish you hadn't asked?
"Direct" vs. "Mixed" Audio
Q: The latest update for the Playstation 3 added a new option for outputting Blu-ray audio. You can now select whether you want "direct" or "mixed" sound. Direct simply outputs the audio track as-is to the receiver, and mixed will combine button and menu sounds into the audio stream. My question is how this might affect quality. I would imagine that with lossless tracks, the output would remain unchanged except when a sound needs to be combined, since the recompressing to a lossless format doesn't actually lose any data. At least this would be ideal, but I wonder if the sound is constantly running through some actual audio processing and being changed whether a sound is being played or not in this mode. I would definitely think that lossy formats would need to be decompressed then recompressed to combine sounds, affecting quality since the compression does lose information. I'm just using "direct" for now, but I think I will probably run into some menu based extra feature that doesn't work right in this mode.
A: The first and probably most important thing to note here is that the player should only be live-mixing these button or menu sounds into the audio signal while the disc's menus are on screen. This function may also be needed to incorporate the Secondary Audio track while "Bonus View" picture-in-picture supplements are being watched. However, the player should not be tampering with the movie soundtrack itself during the course of regular (non-supplemented) playback. With that in mind, this question is somewhat academic. To my mind, lossless fidelity isn't particularly necessary for menu audio or supplemental content like commentaries and PiP features.
To answer your question, in order to live-mix in additional sound elements like this, the player must first decode the soundtrack on the disc to PCM, then add in the new sounds. Depending on the player's abilities and how you have it set up, the machine may then output the resulting combined track as PCM, or re-compress it to one of the Dolby or DTS formats. Most Blu-ray players re-compress only to lossy Dolby Digital or DTS, thus causing a degradation of audio quality. Unfortunately, I don't have a PS3 Slim. (I only have the original model that can't bitstream HD audio in any case.) Therefore, I can't speak for how the Slim handles this.
My recommendation is to leave the player in "Direct" mode by default, and only turn on Secondary Audio ("Mixed" mode) when you specifically need it. That's the safest option.
Are All Blu-rays HD?
Q: Is every Blu-ray disc always recorded in HD? With more and more movies being re-released on Blu-ray, does this mean that you will automatically get a full HD version on Blu-ray, significantly better than the equivalent movie released on DVD? How can you tell by looking at the disc cover?
A: To the best of my knowledge, all Blu-rays released to date have been authored with the primary content on the disc (the movie/TV show/concert, etc.) encoded at some HD resolution. However, many discs contain bonus features that may be encoded in standard definition.
But that doesn't tell the whole story. Note that I specifically said that the content is encoded at an HD resolution. That doesn't necessarily mean that it originated from a high definition source. Although fortunately a minority, some movies and programs may start out in standard definition format, which the studios then upconvert to HD before pressing onto the discs. These offer little advantage over watching a DVD and letting your disc player or HDTV upconvert the picture.
Take the upcoming release of '9 Songs', for example. That movie was shot with standard definition video cameras. As a result, the Blu-ray will be upconverted from SD. This is also a very common problem on many anime titles available on Blu-ray.
If there is any benefit to watching such content on a Blu-ray rather than a DVD, these discs do (usually) still offer an upgrade in sound quality to a lossless format.
Unfortunately, the studios rarely label such discs with sufficient information to let you know what you're buying. You'll have to check disc reviews on sites such as ours to get the full scoop.
The HD Advisor knows many things, but he doesn't know everything. Some questions are best answered with a consensus of opinions from our readers. If you can help to answer the following question, please post your response in our forum thread linked at the end of this article. Your advice and opinions matter too!
Q: I have a 40 GB PS3 and have had it since some time in 2009. My firmware has been updated and currently shows 3.21. I have been trying to play various Blu-ray movies (both older and new releases) and been having a lot of problems during playback. Sometimes the movie just pauses for no reason and suddenly jumps to the next chapter. Sometimes it will pause, then speed up and then play, and other times it just pauses and won't continue to play. I take the disc out and try to clean the disc with a lint-free cloth and the problem still exists. There were a few times when I took the disc out of the player and inserted it back in I got an error that said, "Invalid disc."
Check back soon for another round of answers. Keep those questions coming.
Joshua Zyber's opinions are his own and do not necessarily reflect those of this site, its owners or employees.
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