Q&A # 163 - February 16, 2000

Staff

Q I am interested in adding DTS capability to a home theatre system. I have tentatively selected the Sony DVP-S330 DVD player, as it can be found priced below $300 and definitely states it has "DTS Out". I had planned to pair it with a Sony receiver, either the STR-DE635 or the STR-DE835. The 835 literature expressly states that it has a DTS decoder, so I'm sure that would work nicely (but for another $100 beyond the street price for the 635). Where I become confused is with references to "5.1 channel capability". Some of the product literature seems to suggest that if your DVD player can output 5.1 signals and your receiver can input 5.1 signals, that's all you need for receiving Dolby Digital (AC-3), DTS, and any other encoding system that can throughput "5.1" connections. For example, it is clear that the Sony STR-DE635 (because it has its own built-in Dolby Digital decoder) can handle that audio standard. Is that so regardless of which connection is used, i.e., fiber-optic, digital coax, or 5.1 channel RCA jacks? I had intended to connect the DVP-S330 DVD player to either Sony receiver via the optical or coax digital connection, as opposed to using the analog 5.1 channel RCA jacks. Since the Sony STR-DE635 doesn't incorporate its own DTS decoder, I presumed that if I bought it, I would have to settle for Dolby Digital-encoded program material. However, that receiver's owners manual seems to suggest that while a DTS signal cannot be received through the optical or coax digital connector, a DTS signal COULD be delivered to the receiver through the "5.1" analog RCA jacks. However, I'm guessing that while you may get some audio that way, it won't be in DTS. The DTS and DD formats aren't compatible so you can't play it as though it were DD, and what is likely to happen is that the DE635 will likely "backwards convert" the DTS signal to Dolby Pro Logic sound, right? So my questions: 1. DD and DTS-encoded audio signals can be delivered from DVD player to receiver by several alternate means: fiber-optic digital, coax digital, or analog "5.1" jacks. Is it true that delivering DVD audio signals to receivers via the (optic or coax) digital connectors will only produce satisfactory audio if the receiver has its own audio decoder? 2. What sonic features are "lost" if a DVD player with DD and/or DTS audio output is connected to a receiver with DD and/or DTS decoders via the analog "5.1" RCA jacks, as opposed to using the optic or coax digital connectors? 3. In my case, debating whether to save $100 or so by buying a receiver with a DD but no DTS decoder, what ways, if any, exist to retrieve a DVD's DTS-encoded audio and deliver impressive audio? I'm assuming that the Dolby Digital decoder will not accept DTS-encoded audio signals, and I'm assuming that if the receiver accepts the DTS-encoded audio at all, perhaps by using the analog "5.1" RCA jack connection, the resulting audio will be converted to Dolby Pro Logic. In other words, it appears that to properly hear and appreciate DTS-encoded program material: (a) it must be played on a DVD displaying the "DTS Out" logo, (b) it must be played by receiver with its own DTS decoder, and (c) that will only work if the DVD player and receiver are connected by fiber-optic or coax digital connectors; and will NOT work if delivered through their "5.1" analog RCA connectors. Thanks very much for tackling a very confusing issue to someone who cut his audio teeth building Heath and Dyna kits, and loved Acoustic Research (AR) bookshelf speaker systems.

A DVD players will output DD as a digital bitstream through the coaxial or Toslink optical digital jacks. That signal has to be conveyed to your receiver with the appropriate cable to the digital input on your receiver, where it will be decoded if the receiver has DD decoding built-in. The 5.1 analog output jacks on the DVD player will output decoded DD as well, and those signals are conveyed to the receiver using coaxial cables, and connected to the set of 5.1 analog jacks, if your receiver has them. For DTS, it is different. Only the digital signal is available from the DVD player, and only on those players that specify DTS-out (pretty much all new players now). The 5.1 analog output jacks on the player don't convey decoded DTS, at least not the current players. So, for DTS, you need an external DTS decoder or the DTS decoder in your receiver. DD and DTS require DACs that will decode those specific signals. A DD DAC, whether it is in your DVD player, external decoder, or in your receiver, will not decode DTS. If you do not have a DTS decoder anywhere in your system, you need to use the two-channel analog outputs from your DVD player going to analog input jacks on your receiver, where the audio will be decoded into Pro Logic.

Q A few years ago, I set up my family room with a 60" big screen TV and a Yamaha RX-V490. I am disappointed with the quality of the sound from most movies and from most all of my CDs. Is this a quality receiver? Should I be looking at perhaps the RX-V 795A? I want the quality of sound that you get in model home theaters.

A Model home theaters vary in quality, but they are usually very good. I would suggest going to the Yamaha RX-V995.

Q Back in Q&A 136, you stated that, for a non-DTS rated DVD Output player, "it is unlikely your player will recognize DTS DVD's. However, it will play DTS CDs". How is it that a non-DTS Output player can properly handle DTS-encoded CDs but not DTS-encoded DVDs? Did legal roadblocks for DTS only impact DVDs?

A DTS CDs use 48 kHz 20 bit signals coded in PCM (conventional CDs use 44.1 kHz 16 bit PCM), so your player will send the signal along to a DTS decoder, such as in your receiver. Any CD player (including a DVD player with a CD in the drawer) with a digital output jack will send the DTS bitstream out. However, for DVDs, DTS is restricted from using a conventional PCM track (but it's also 48 kHz 20 bit). It requires a specific flag that only DTS-out DVD players know how to recognize. So, yes, the legal issues only affect the DVDs.

Q The owner's manual for the Sony STR-D635 contains the following puzzling quote: "When making digital audio connections to a DVD player, connect to either the coaxial OR optical digital jacks, and not both. It is recommended to make digital audio connections to the coaxial jack". 1. After parting with $29 for a Toslink optical cable, I found the above quote! What reason would Sony have for preferring a coaxial digital connection over a fiber-optic one? 2. If I elect to get a coax cable, would this be anything other than a high-quality video cable with RCA plugs on each end?

A Your Toslink cable is fine. In fact, they are beneficial from the standpoint of having one less ground loop to worry about. With coaxial, there is also the issue of impedance, and that is not a problem with optical cables. We are experimenting now with testing jitter and comparing Toslink to coax, since the RCA jacks on transports and receivers may not always be 75 Ohms, nor are all coax cables 75 Ohms.

Q I am finally putting together what I consider a good stereo system. I have a Rotel CD player (970BX), a Yamaha Receiver, and Paradigm speakers. I'm not much into Surround Sound so it's set up for just listening to music. I've been seeing some stuff on the net about Digital-to-Analogue converters and now I'm wondering what one can do for my sound.

A DACs can indeed improve the sound, but not necessarily. It will depend on the quality of the outboard DAC, but also the cables and connections. We have a new DAC that upconverts to 96 kHz, so we are very interested as to what this can do for an inexpensive CD player that has a digital output but not a very good DAC inside. More on this as we proceed with testing.

Q I recently was given a DVD player as a gift. I'd like to play it on my TV but the TV only has a single coaxial input. I can't run the DVD player through my VCR because the VCR thinks I'm trying to make an illegal copy of the DVD and the signal keeps fading in and out annoyingly as a result. Is there any piece of inexpensive equipment I can buy so that I can watch my DVD on my old TV?

A I have actually seen a few TVs with only a coaxial input for the video and no inputs for audio. What I would suggest is using the coaxial video output from your DVD player going to the coaxial input on the TV, and using the audio outputs from the DVD player going to your VCR or directly to your receiver.

Q I have a Denon AVC-A1D (THX Ultra) which I believe is the same as the Denon 5700, and the manual state a minimum 6 Ohms impedance for the speakers. But due to the lack of research I have bought a set of M&K LCR-750THX Select speakers for the front sound stage and M&K 550 THX surrounds, all of which seem to be 4 Ohms. I would appreciate your views on what problems I might encounter with this setup if any. I don't run the system at very high volume levels, and the amp doesn't seem to get very hot, but I was wondering would there be any loss in sound quality?

A As long as you don't play the system really loud, you should not have any problems. The fact your receiver is working OK and not getting hot is a good sign you are doing the right thing. It should not affect the sound quality at all, when using it like you are now.

Q I've been looking around at "HDTV Ready" wide-screen TVs from both Toshiba and Mitsubishi. As you know, when watching standard 4:3 television, these TVs place gray bars on the sides of the image to fill out the screen. How big of a concern is the problem of burn-in? The Mitsubishi website says that you shouldn't watch more the 15% of 4:3 television weekly. Since virtually all programming is still 4:3, that's kind of difficult. The thought of stretching the image to fill the screen is really not a solution as far as I'm concerned. The Mitsubishi site did say "black bars". Are they maybe referring to last years model? Do the gray bars resolve the problem? I think it will be a long time before 85% of the programming is in 16:9.

A Burn-in can be a problem if you watch movies that have black bars, and the movie image is bright and contrasty. The gray bars put some image onto the screen, and thus, those areas are "burned-in" about as much as the rest of the screen. Regardless of whether your TV has black bars or gray bars, you should watch your movies with not so much brightness and contrast as they tend to come out of the box with their default settings. It is not only better for your TV, but better for your eyes. In other words, turn the brightness and contrast down, no matter what kind of TV image you are watching.

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