Q&A # 274 - February 13, 2002

Staff

Q Is there any big difference between Dolby Digital and DTS sound for DVD movies?

A Dolby Digital uses more compression, but it is also more efficient than DTS. Early on, DTS had a high bit rate, but over the past couple of years, DTS DVDs have used a DTS bit rate only 1/2 the rate that they used to. The bottom line is that there have been no scientific studies that suggest one sounds better than the other. We have been offered the use of a Dolby Digital encoder, but DTS has not responded to our requests for a DTS encoder so that we can perform the scientific tests. In the meantime, don't worry about it. Just enjoy the movie.

Q My receiver does not support Dolby Digital. Is it worth getting a DVD player with built-in decoders if I don't plan to buy another receiver?

A Yes, it sure is worthwhile, because DD and DTS are both far superior to the old matrix surround sound (Pro Logic). You just have to make sure your receiver at least has a set of 5.1 analog input jacks to receive the 5.1 analog outputs of the DVD player.

Q I am considering purchasing a separate surround sound processor (Classe SSP30 or B&K ref 30). I listen to 70% home theater and 30% DVD-Audio/2 channel stereo. My goal is to obtain a clearer sound on surround material as well as clearer dialogue. I am trying to keep the budget for this upgrade to around $3k or less My question to you is this: Will I get a performance upgrade from using one of these products? I am currently using a Yamaha DSP-A1 as my processor.  Is the preamp section in these so-called high end products really that much better than the Yamaha?

A Although the DSP-A1 is a very good product, high-performance dedicated processors will likely be better as a preamp. What I have found is a tighter bass and less harshness. However, we are not talking 10 times better. The last 20% is what you get for the additional money when you purchase a high-performance product. Also, it matters what you mate the processor with, in terms of the resulting sound. You can't just pair any great processor and any great power amp to get a preferred sound. You have to do your homework and go out to dealers to hear them. For example, I currently have a Balanced Audio Technology VK-500 power amplifier and a McIntosh MC-602 power amplifier. Both are terrific, but they sound different from one another. One is not better, just different.

Q I have a pair of Bose speakers, rated at 4 Ohms, some PSB speakers, rated at 6 Ohms, and I am looking at some other speakers, rated at 8 Ohms. What should I do when using all of them with my receiver?

A Use the 4 Ohm setting on your receiver, and adjust the loudness of each pair using a test disc, since 4 Ohms will draw more current than 8 Ohms. Other than that, you should be OK.

Q Could you clarify your answer in Q&A 271 regarding IEEE 1394 and how it is the best way to convert HD signals? I have a Mitsubishi WS-55907 TV (2001 model) and I am (was) looking into buying a HD satellite receiver. I spoke with Mitsubishi and according to them they will offer by mid 2002 a $1,000 upgrade to my model that adds an IEEE 1394. Does that mean the HD satellite receiver needs a IEEE 1394 output as well? Also, will it be possible to have a DVR/HD satellite receiver or will the DVR component affect the HD signal to the T.V.?

A We are editing an article on the various formats right now, and it should be published shortly. The use of one connection over another is a competitive matter. DVI, IEEE 1394 (Firewire) and SDI are all competitors. Firewire allows multiplexing, so that you could have several components output connected to the TV through Firewire, and you select which one you want to watch. DVI can't do that. DVI seems more oriented to copyright protection than customer convenience, and it makes us pretty angry. In any case, you will need the same format output on the satellite box as the TV to use them. So, for DVD, you need a DVI output on the sat box and a DVI input on the TV. Same for Firewire. I think they should have used Toslink optical for digital connections. Two reasons: one is that you can use long cables and maintain bitstream integrity; the second is that there would be no possibilities of ground loops. Although the digital stream itself would not be affected by the ground loop, the analog circuits in the connected components would. Toslink has gigahertz bandwidth too, so it could handle 1080i and even 1080p from a digital scaler. Remember also that DVI and Firewire are specifications, not the mechanical anatomy of the jack. So, both of these formats could be run through Cat5 or Toslink if they wanted to.

Q I have a  question about sub placement. I wanted to place two identical subs besides my two front speakers (I think it would look better than stacking them on top of each other) and I know that placing the subs like that could cancel out some of the out of phase frequencies and so you could actually reduce the SPL placing the subs that way.

My question is that if one of the subs has a variable phase crossover that would enable me to vary the phase from anywhere between 0-180 degrees, couldn't I adjust the phase of that sub so that none of the frequencies from the two subs are canceling each other and I get the SPLs from both the subs to add up?

A Yes, the phase control will help. However, you may not need it. Turn on both subs and run a low frequency test tone through the system. Place an SPL meter (e.g., Radio Shack) in the listening position and vary the phase of the one sub until you get the maximum SPL. The setting may be optimal only at one frequency, so use something around 30 Hz to set them.

Q I recently bought a Sony STR-DE475 receiver for a great price. I previously had a Sony Pro Logic receiver and was in need of an upgrade to DTS and Dolby Digital. I placed the new receiver next to the TV in the same place where the old one was. After a few weeks it began putting a greenish cast on my TV screen on the side closest to the receiver. Is there something in the Sony that is not shielded? Are newer TV's shielded? (My current TV is old  and in need of an upgrade anyway.) Am I going to have to go the cookie sheet route?

A The power supply transformer is alternating current, so it is unlikely to be the culprit. Something is producing a fixed magnetic field inside the receiver chassis. Perhaps the chassis itself is becoming magnetized, assuming it is steel. Either move the receiver a little farther away, or yes, try the steel cookie sheet method.

Q I read the question regarding a component-to-Scart cable in Q&A 258. I just noticed that there is a Neotech cable that should do the trick. Available online at http://www.dvdshop.com.au/accessories.html.

A Thanks for the info.

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