HD Advisor: Pop Song 89

Posted Fri Jan 14, 2011 at 12:15 PM PST by

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]

If you've already sent a question and don't see it answered yet, please be patient as we work our way through them. To browse through previously answered questions, visit the main HD Advisor page.

Answers by Joshua Zyber

Anamorphic Lens for 2.35:1 Projection

Q: I have a 1080p projector and have considered adding an anamorphic lens for widescreen "scope" Blu-ray releases, but something confuses me. My projector will completely fill the frame vertically by interpolating extra lines off a Blu-ray disc, which an anamorphic lens would then squash back to a 2.35:1 widescreen picture. Although all 1080 lines are in the squeezed image, is this really any better than just watching the picture with the reduced (fewer than 1080) number of lines, since the extra lines are interpolated anyway? Widescreen pictures look really good now without an anamorphic lens. Is there that much to be gained? I believe it's a different story with DVDs since widescreen pictures are stretched vertically on the disc to occupy more lines, and a real gain in the number of lines in a restored (vertically squeezed) image results. But as I understand it, this isn't the case for BDs.

A: If you haven't already, I recommend that you read my Constant Image Height Tutorial, which gives an overview of what you're describing.

Fundamentally, your understanding of the process is correct. Blu-ray discs are not authored with any sort of anamorphic enhancement, like you see on DVD. All movies on Blu-ray (well, most of them) are encoded at a resolution of 1920x1080 square pixels. Any movie with an aspect ratio of 2.35:1 will be letterboxed within that frame. The active move portion of the image occupies approximately 1920x800 of those pixels. The other 280 rows of pixels make up the black bars.

There are two methods for projecting a letterboxed 2.35:1 movie onto a 2.35:1 screen. The first is to simply zoom the image so that the movie fills the screen and the letterbox bars spill off the top and bottom. In a darkened room, the black bars should barely be visible. If they're at all distracting, some dark fabric above and below the screen is an easy way to absorb that extra light.

The more complex method is to add an anamorphic lens that will stretch the 1920x1080 image output from the projector into a 2.35:1 shape. You will then need to electronically scale the image back to its proper picture geometry by cropping off the black bars entirely and stretching the middle portion in a vertical direction. Many home theater projectors offer this feature nowadays, and it sounds like yours is one of those models. You are absolutely right when you say that any new pixels being added to the picture are all interpolated.

The anamorphic lens method has three advantages. By cropping off the letterbox bars, there's no chance of that extra light spill distracting you or washing out your movie image. More importantly, by redirecting all of the projector's 1920x1080 pixels onto the 2.35:1 screen, you're focusing more light onto a smaller area. This will result in a brighter movie picture, which can be very helpful with large screen sizes where every lumen makes a difference.

The third advantage is that, by packing all of those pixels into the smaller area, you also reduce the size of each, and minimize any visible pixel structure (the "Screen Door Effect") in your picture. This is less of a concern with 1080p projectors than it was with older, lower-resolution models. But it still could be an issue, once again, with those large screen sizes.

The downside to anamorphic lenses is that they are very expensive, and can cause pincushion distortion in your picture geometry (generally mild) at short throw distances. You'll also need to decide whether you want to remove the lens when watching regular 16:9 content, or scale your picture into a pillarbox format. The latter will reduce your picture resolution in that mode. There are some anamorphic lenses that let you switch to a "passthrough" mode without any stretch, but these tend to sacrifice image quality at both aspect ratios in the name of convenience.

In the end, both the zooming method and the anamorphic lens method have their advantages and disadvantages. Neither is necessarily more "correct" than the other. Which one you decide to use will depend on the specific circumstances of your home theater room, your personal priorities, and of course your budget.

PS3 Settings: LPCM vs. Bitstream

Q:If both my A/V receiver (Denon 2808) and Blu-ray player (PS3) can decode HD Audio formats, which is the preference for doing it? I have the older PS3 (not slim), and I've heard that it still dumbs down HD audio formats before sending them if you have PCM set...is this true? I suppose on the Denon, either way I should have "Multi Ch" selected when watching a Blu-ray, correct? I see the PS3 and Denon are similar to your setup, so how do you have yours set up?

A: In a situation where a Blu-ray player can either decode Dolby TrueHD and DTS-HD Master Audio internally or transmit them in native bitstream form, there shouldn't be a lot of difference between these two options. Both would provide you with the full lossless track. Theoretically, the Bitstream option may be less prone to jitter, but whether that makes any audible difference to your ears depends highly on whether you classify yourself as an "audiophile" and buy into that belief system or not. (In other words, Placebo Effect will play a strong role in your perception.)

As a matter of convenience, the internal decoding option will allow you to listen to Secondary Audio content, such as menu sound effects or any soundtrack that accompanies a Bonus View supplement. Secondary Audio must be live-mixed with the movie soundtrack, which can only be done if the player decodes. The Bitstream option will only send the movie soundtrack itself. If you wanted to listen to Bonus View content, you'd have to turn off Bitstream and then turn it back on again when done. This can be a minor nuisance.

With all that said, the original ("fat") PS3 cannot transmit the native bitstreams of either DTS-HD Master Audio or Dolby TrueHD. The console will downgrade to standard DTS 5.1 or Dolby Digital 5.1 when the "Bitstream" option is selected. However, it can decode these formats internally. As such, you should set the console's audio for LPCM output and let it do the decoding. Only the newer PS3 Slim is able to bitstream HD audio.

Homework Assignment: You Be the Advisor

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!

Blu-ray Playback on a PC

Q: I'd like some help with Blu-ray playback on a PC. What's the best Blu-ray playback software, Powerdvd9 or WinDVD 9? For PC HD Audio, what are the best HD sound cards? Are there any obvious downsides to HD Audio over analog from a PC? What are the best setting on a PC for outputting the 1080p picture? My full HD projector receives a signal from my Blu-ray PC at 1080/60 – should I set the PC graphics card to 1080/24?

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.

See what people are saying about this story in our forums area, or check out other recent discussions.

Tags: Joshua Zyber, HD Advisor (all tags)