HD Advisor, Class of '92

Posted Fri Feb 4, 2011 at 11:15 AM PST by

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Answers by Joshua Zyber

Dolby Digital 5.1 Audio from a Laserdisc Player

Q: Is there any other way to get Dolby Digital AC-3 audio from my CLD-99 Pioneer Elite Laserdisc player other than connecting its RF output to some compatible AC-3 RF input? What about using the CLD-99's coaxial or optical digital audio outputs? Until a couple of months ago, I had a Pioneer VSX-906DS receiver as my audio amplifier. I used to connect the CLD-99's coax digital audio output to the 906DS's coax audio input. (It says "AC3/PCM" on top of that input. This receiver was made around 1996/1997.) I had full Dolby AC-3 multi-channel audio playing. A couple of months ago, I got a brand new Marantz SR 6004, which supports every available audio codec. Everything else works ok, except the AC-3 audio from my CLD-99, connected to the new receiver through the same old coax digital audio output. The SR6004 only recognizes the audio coming from the CLD-99 as Left & Right PCM channels. I hope you may shed some light on this issue. Since I still have an LD collection over 700 titles large, if left with no other choice, I'll have to use a dual-receiver setup!

A: This question feels like a blast from the past. The short answer is that it's possible to get Laserdisc Dolby Digital 5.1 to your current receiver. Unfortunately, the long answer is that it will be both a hassle and likely expensive.

Dolby Digital audio (also known as "AC-3") was introduced to the Laserdisc format very late in its life, starting in 1995. (The last American discs were released in 2000.) Laserdiscs themselves were limited to two digital audio channels plus two analog audio channels. The vast majority of Laserdiscs contain a stereo encoding of the movie's soundtrack in uncompressed PCM format that fills both digital channels. In order to ensure backwards compatibility with older equipment, this remained the case even on discs that offered Dolby Digital. To get around this, the AC-3 5.1 track was encoded in RF modulated form onto one of the disc's analog audio channels. Therefore, a disc could have the PCM soundtrack on the digital channels, AC-3 on one of the analog channels, and one more analog channel that might be used for either an audio commentary or a mono version of the soundtrack.

To get Dolby Digital 5.1 off a Laserdisc, you need to start with a Laserdisc player that specifically has an AC-3 RF output. (Your CLD-99 qualifies.) The AC-3 track can only be transmitted through that AC-3 RF output. It cannot be transmitted through a normal coaxial digital or Toslink optical connection. The RF output will also only transmit the AC-3 track, not any other audio format.

The AC-3 signal must then be fed into an RF demodulator that will convert it to a standard S/PDIF digital format that your receiver can decode. In the late '90s, some receivers were manufactured with an RF demodulation feature built-in. This would be the "AC3" input on your Pioneer VSX-906DS. Connect the AC-3 output on the LD player to the corresponding input on the receiver, and then the receiver will both demodulate and decode the Dolby Digital 5.1 soundtrack.

After the death of the Laserdisc format, receiver manufacturers stopped including the RF demodulation feature. It's no longer needed in the DVD or Blu-ray era. Your newer Marantz receiver will not be able to demodulate the analog AC-3 signal on its own, and therefore will not be able to decode the DD 5.1 track.

In order to continue listening to Laserdisc Dolby Digital 5.1 on your new receiver, you'll need to add an external RF demodulator device. These were marketed in the late '90s, because not every Dolby Digital compatible receiver at the time had the demodulation function built-in by default. RF demodulators are generally small, simple components. You plug the LD player's AC-3 RF output into the demodulator, and the demodulator will convert the signal to a standard S/PDIF form (via either coax digital or Toslink optical outputs) that your receiver will accept and decode. The more elaborate models might allow you to switch between the LD player's AC-3 feed and a regular digital connection so that you don't have to use up an extra digital input on your receiver. You can find a list of common RF demodulator models and the features they offer on the Thad Labs site.

(Be careful not to confuse an RF demodulator with an RF modulator, which is a completely different device.)

Back in the day, RF demodulators used to sell for around $200. Today, you'll have to hit up eBay and hope to find a decent deal on a working unit.

For what it's worth, DTS on Laserdisc is much easier. DTS discs forego any pretense of backwards compatibility and simply store the DTS track on the disc's two digital channels in place of the normal PCM stereo option. You can transmit this through the player's coax or Toslink outputs and feed it directly into your receiver, the same as it works on DVD.

I'll be honest, I often counsel new Laserdisc owners not to bother with Dolby Digital at all. Because it was introduced so late in the format's life, only a small selection of discs even offer the option. Frankly, it's hardly worth the effort. However, since you already have a substantial collection of discs and were already accustomed to listening to the 5.1 tracks when available, I'll leave it to you to decide whether to hunt down and pay for an RF demodulator or not.

4:3 Aspect Ratio on HD Broadcast

Q: A few friends of mine had an argument about movies shown on an HD channel as a 4:3 picture with bars on the side (pillarbox). The argument was simple: I always believed that even though the film is in standard format shown on an HD channel, it is still HD unless the transfer is not in high definition. My friends are under the impression that because it is not 16:9, it is not an HD picture. 'Casablanca' and 'Wizard of Oz' on Blu-ray are HD pictures but in the 4:3 aspect ratio. If I am right about broadcast HD, how can I convince my friends that it is an HD picture even if it is 4:3?

A: Your friends are confusing aspect ratio with resolution. A high definition picture can be presented in any aspect ratio, not just 16:9. A huge number of movies are available on Blu-ray letterboxed to a 2.35:1 aspect ratio with black bars at the top and bottom of the image. These are still high definition, even if they don't fill the HDTV screen.

Likewise, classic movies (such as 'Casablanca' and 'The Wizard of Oz', which you cited) that were photographed at the "Academy Standard" aspect ratio of 1.37:1 will be pillarboxed into the center of the frame with black bars on the sides. These are also still high definition. The active portion of the image that contains the movie picture is much higher resolution than the comparable DVD releases or standard-definition TV broadcasts. You can point your friends to my Why Don't the Black Bars Go Away? article for more detail on this, including plenty of pictures to illustrate the concept.

With that said, it's worth noting that not everything broadcast on an "HD" television station is necessarily high definition. Many channels routinely air standard-definition content that's been upconverted to the higher resolution. Sometimes this might be pillarboxed, and sometimes not. (Often, 4:3 movies are stretched to fill the screen.) Rather than try to judge based only on aspect ratio (which can be misleading), you should look instead for how much detail is available in the image. The difference in detail between true HD and upconverted SD on a broadcast channel is usually easy to see if you pay attention to it.

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!

Audio Settings on PS3 Slim

Q: I have a PS3 (Slim model) hooked up to my A/V receiver (Yamaha RX-V565) via HDMI 1.3 cable connection. I am trying to get the PS3 to decode the bitstream tracks from my Blu-rays. It sounds trivial, but I want to see my Yamaha receiver display the Dolby Digital or the DTS-HD Master Audio track on the front panel instead of just seeing PCM all the time. I have gone to the PS3 menu and selected the audio settings option. From there, I selected the connected media (HDMI) and all the available sound options (i.e. DD, DDPlus, D True HD, DTS, and DTS HD Master Audio). But yet in spite of doing all the above, my Yamaha continues to display PCM. I also have a Panasonic Blu-ray connected to the Yamaha and it displays the audio selection properly. Even after speaking to the customer support center (who were unable to further help me), I am back to Square One. What have I done wrong? What don't I get? I need your help.

JZ: I only have the 40 GB version of the original ("fat") PS3, not the newer Slim model. The fat PS3 cannot transmit the native bitstreams for the lossless audio formats, but the Slim model can. There should be a "bitstream" audio selection somewhere in the setup menus. I'll have to leave it to some of our other PS3 Slim owners reading this to direct you to where exactly in the menu that's located.

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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