28 HD Advisors Later

Posted Fri Sep 18, 2009 at 12:00 PM PDT by

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Answers by Joshua Zyber

HD Audio Decoding

Q: I use a PS3 for my Blu-ray needs. This player has what some believe to be a handicap in not being able to bitstream the HD audio codecs to a receiver. Is there a difference in decoding capabilities and/or quality in different components? Will my PS3 decode the DTS-HD Master Audio signal as well as my Onkyo 709 receiver? Would I get better sound from the same media with a standalone player that bitstreams to the receiver, and lets the receiver do the decoding?

A: This is still an area of anxiety for many Blu-ray (and specifically PS3) owners, mainly because allowing the disc player to decode the audio internally prevents a Dolby TrueHD or DTS-HD MA logo from lighting up on their receiver's front panel.

The Dolby and DTS compression codecs must go through three stages before sound comes out from the speakers. First, the codec must be decoded to PCM format. Then that PCM must be converted to analog. Finally, the analog signal is amplified out to the speakers. The second step (D-to-A conversion) will have by far the biggest impact on overall sound quality. The quality of DAC components is one of the biggest distinguishing features between entry-level and high-end hardware.

When using a PS3 connected by HDMI, your D-to-A conversion still takes place in your receiver, not the player. So you're still relying on the receiver to the heavy lifting. All the PS3 does is the decoding.

At least in theory, the decoding stage is a pretty straightforward process. If we think of the lossless Dolby TrueHD and DTS-HD Master Audio formats as being like ZIP compression files, then decoding the formats is like unzipping those files. If everything is working properly, you'll get a 100% perfect copy of the original source. If something isn't working properly, the file will be corrupted. Generally, this means that the movie soundtrack will be unplayable or horribly distorted, and you'll know it right away.

As such, it really shouldn't really matter whether you do your format decoding in the disc player or in the receiver. Assuming that the hardware is working correctly, one component won't decode better than another. Either they work or they don't.

However, the transmission process of sending the signal from the player to the receiver may be an area of concern. If you decode the format to PCM at the disc player, the transmission of PCM from one device to another could be susceptible to jitter. On the other hand, the undecoded compression formats have clocking mechanisms that make jitter much less likely when transmitted in bitstream form.

There is much debate in audio circles about whether human ears can really hear the effects of jitter. Of course, members the audiophile crowd insist that their golden ears can discern even the most microscopic timing variations between the arrival of one bit and the next. Scientific double-blind testing usually reveals otherwise, unless the jitter is particularly egregious. But that's probably an argument for another day.

The long and short of it is that, barring extraordinary circumstances, decoding the audio inside a disc player should be just as good as doing it in the receiver. But if seeing a Dolby or DTS logo on your receiver's front panel makes you feel reassured that everything is working properly, by all means seek out a player that can send the native bitstreams.

I'll be honest, I set my standalone player to bitstream its audio, even though it has the necessary internal decoders. I like seeing those TrueHD and Master Audio indicators on my receiver's front panel. However, if my only Blu-ray player were a PS3, I doubt that I would go out of my way to purchase another player just for that feature.

TV Calibration

Q: My HDTV has about 6 or 7 different settings to fiddle with: contrast, color temp, etc. Can you give me a rundown on what numbers settings should be for the best picture? I have the Philips Ambilight 42".

A: Unfortunately, it's not as simple as one person telling you what numbers to use. TV calibration settings will vary from set-to-set depending on the brand and model, manufacturing tolerances from one unit to another, and the conditions of your viewing environment. Even if you search online and find someone with your same model, any settings they recommend should really just be used as a starting point. Certain tips, such as which processing functions to turn on or off to make the picture better or worse, may be universal. But the specific numbers for where to set your Brightness, Contrast, Color, etc. will be specific to your TV and room.

Ideally, you should hire a professional calibrator to fine-tune your set for its best performance using color analyzers and other professional equipment for precision measurement. If that's out of your budget, at the very least you should purchase a calibration disc like 'Digital Video Essentials' and follow its instructions for adjusting your TV's user-accessible controls.

Service Menu Adjustments

Q: I just purchased my final component to my home theater, a Panasonic TC-P46G10. I'm quite sure I'll be satisfied with it. According to all the reviews, it performs very well and has many great features, of which they all say that THX mode is the best. However, one review of the panel says that, "a calibration that accessed the service menu could increase light output in THX mode, but we don't perform such calibrations as part of our TV reviews." Is finding how to access the service menu and then changing the correct settings worth pursuing? Will it void any of my warranty?

A: Your TV's service menu is intended to be accessed only by qualified professional calibrators and technicians. That's why it's hidden from public view, and can only be entered through a secret combination of buttons on the remote and/or front panel. Although there are many sources online that may provide the service menu access instructions for your set, entering this menu yourself will void your warranty.

As a general rule, I don't recommend going into the service menu unless you know what you're doing. There are many settings in there that, if changed incorrectly, can seriously distort or even disable entirely your video image. Most of them will not be labeled with clear descriptions of what they are or how to adjust them. You don't want to accidentally change a setting without knowing how to change it back (or even what to change it back to).

With that said, I know that there are many hobbyists who will do this anyway, some for curiosity and some who are genuinely knowledgeable enough to make service menu adjustments on their own. Frankly, I've done it myself on some TVs I've owned. For anyone brave (or foolish) enough to do this, I strongly recommend carefully reading the instructions for how to change the settings in your set's service menu. What happens when you press which keys on your remote? Is it the Volume key, the Channel key, or something else that advances a particular setting? Learn all this in advance so that you don't mistakenly hit a button without knowing what it will do.

Also, when entering the service menu, the absolute first thing you must do is write down the TV's default settings for each and every option in the menu, no matter how many there are or how long it takes to do. If you change something (either intentionally or by accident) and it makes your picture worse, you will need to know what it should be reset back to.

Really, it's probably best if you just stay out of there and leave those adjustments to professional technicians.

Homework Assignment: You Be the Advisor

Some questions that the HD Advisor receives 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!

Subwoofer Placement

Q: My HT room is 4x6 meters. I'm currently using 2 subwoofers, both front firing -- a 10" sub at the front and a 12" sub at the back. Currently, the front sub is at the left side corner facing the room while the back sub is at the center of the back wall facing the left side wall. Is this the right placement?

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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