Q&A # 97 - January 5, 1999

Staff

Q A great christmas present from one of my kids, which I have enjoyably, very, very enjoyably read cover to cover, states the following: [this is a paraphrase] "forget "surround modes" i.e., stadium, hall, etc., etc. Use Pro Logic, DD, or DTS for movies and no mode at all for music; they "degrade sound quality". I though the majority of 16 bit CDs were in surround sound???!!!?? AND NOW THE SECOND OPINION PLEASE.

A All stereo CDs, whether they are 16 bit, 24 bit, or whatever, and in fact, all two channel stereo sound sources, will decode through Pro Logic, into surround sound. In phase, and identical, signals from the two channels are directed to the center, and out of phase, but identical, signals are directed to the rear. The rest goes to the front left/right. Whether or not the process degrades the sound quality compared to leaving it in two channel stereo is really a matter of preference. Personally, I don't use surround modes when listening to single instrument (like piano) or small ensemble (string quartets) music CDs, but occasionally, with popular music or with orchestras, Pro Logic and Enhanced Pro Logic surround modes can be interesting. I never use hall or stadium-type modes with CDs because I think they sound very artificial. For movies, the various modes are quite useful, and they can even boost the surround sound experience with DD and DTS. For DD and DTS music discs, you should always use the 5.1 surround sound in all the channels rather than any mode that downconverts it to two channel stereo (assuming you have the appropriate sound system), since downconverting will degrade the sound. Some DVD movies have two channel stereo that is recorded in only two channels of the Dolby Digital track. With these, it is necessary to use the receiver's Pro Logic mode if you want surround sound. Otherwise, you can watch these movies in two channel stereo and it won't be a downconversion process or a Pro Logic processed sound.

Q With reference to a November Q&A, I believe that the standards established for DVD require that all 96 kHz-24 bit data be converted to 48 kHz-16 bits before being output to the digital outputs-either coaxial or Toslink. Buying those out-board 96/24 DACs may not be cost effective. This is confirmed in the Sony 300 and Toshiba 2108 DVD manuals. MSB Technology also confirms this and says they can do a modification on DVD players that will output the 96 kHz-24 bit digital data.

There is a rumor that some of the Pioneer DVD players that can be easily modified for "All-Code" DVDs and the elimination of the Macrovision may also be capable of 96/24 digital output either directly or with some easy modification.

A Because of copyright issues, DVD players are supposed to only output the decoded 96/24 sound as analog signals through the stereo two channel jacks on the rear of the player. You can also select 48 kHz digital out, but this has been downconverted from 96 kHz. On some players, there may be a method for getting the 96/24 digital out, but the details are sketchy right now. The 96/24 DADs that I have listened to sound terrific, but I am just going to wait until high performance players and transports are available with 96/24 digital outs rather than mess around with the transport's electronics to try and bypass the restrictions. It will come by itself sooner or later.

Q I'm a hifi newbie and I want to know how important is the THD rating for the receiver. Despite what the specs said 0.02% or 0.7% THD at 100 Watts rms, if someone puts out a couple receivers varying between 0.005% and 0.7% and then blind fold you to test listening to the same CD music, can you/we tell the difference? What's the difference anyway? I don't have the equipment, so I can't test it myself.

A THD specs for receivers are mostly a marketing tool. Unfortunately, it has caused the sound to be worse in some situations, because the use of negative feedback can lower the specification figure. If you look at the specs for high performance amplifiers, the THD will often be in the tenths of one percent rather than in the hundreths or thousandths of one percent. The overuse of negative feedback, while lowering THD, causes other problems, and the result is a sound that is too sibilant (the letter S sounds hissy or mushy), and also, odd ordered harmonics can be introduced, which sound very harsh. The answer to your question is that the amplifier with the 0.7% THD might very well sound better than the one that specifies 0.005%! So, just use your ears to judge the sound, rather than the spec sheet. I have noticed that the most recent mass market receivers use discrete components in the amplifiers, rather than so many chips, and the THD specs are higher than they used to be, so this indicates they are beefing up the amplifiers and using less negative feedback. The resulting sound will be better than it has been in the past.

Q Is it true that keeping the contrast setting low will extend the useful life of a television?

A It is more a function of the overall brightness than just the contrast, and yes, keeping the level down will extend the life of the picture tube. However, it is more important for the benefit to your eyes than simply to benefit the TV. What I do, for computer monitor as well as my TV, is to set the brightness and contrast low. You have to turn them both down in order to get a balanced picture, rather than just one of them. On my TV, I have to turn the color adjustment up somewhat to compensate for the low brightness and contrast. Also, lowering the sharpness control, for me, gives an image that is easy to watch over a long period (several games on the weekend, or a long movie). Additionally, I use a small lamp that shines to the side and rear of the TV on the wall (about 50 watts turned half way down with a rheostat). This lets my eyes adjust to the overall lighting in the viewing area rather than just to the image on the television screen. The eye is like a camera's automatic exposure system. If the viewing area in the room is dark except for the picture on the TV, your pupils will open up to get an overall exposure in the room, and the TV image will be too bright on your retina. This will cause eye fatigue. I keep the blinds on the windows drawn, so that I can get a viewable TV image with low brightness and contrast, and also to reduce reflections from the CRT face. Since the lamp is on the side and aimed behind the TV, it does not cause any reflections from the face of the TV. Most people turn the brightness and contrast up too high on their TVs, and it is very fatiguing. You will get a better picture too, since you won't be overdriving the phosphors on the CRT face.

Q I have just purchased the Yamaha DSP-A1 for my home theater. There is an Impedance Selector for 8 Ohm and 4 Ohm speakers at the back of the amplifier. My main speakers are Monitor Audio 703 PMC (8 Ohm) with Monitor Audio CC700 (6 Ohm) as Center speaker, a pair of Energy RVSS (6 Ohm) for rear effect and a pair of JBL (8 Ohm) for front effect. Would you please tell me which position for the impedance should I set it to? Also, please explain to me the bad effects if I have switched to a position that does not fit my speakers?

A In the case of the DSP-A1, which uses a different (better) amplifier design than in their other models, and for your particular speakers, I would say that the 8 Ohm setting is fine. If you were using all 6 Ohm speakers, and obviously, for all 4 Ohm speakers, it should be the 4 Ohm setting. For the more modest receivers, I would recommend using the 4 Ohm setting for a mix of 6 Ohm and 8 Ohm speakers. If you used the "wrong" setting, you would find that the amplifier overheats, and it would sound mushy and harsh at high volume. The 4 Ohm setting limits the voltage on the output transistors, thereby limiting the amount of current that can flow, and this will reduce the chances of clipping.

Q I was wondering if you would be able to answer a question concerning my turntable. Whenever I play a record, the midrange drivers in my speakers move an inordinate amount even at low volumes. This does not occur when playing a CD even at a much higher level. I am afraid about damaging my speakers due to the excessive excursion. What is causing this and how can I fix the problem?

My System: Linn LP 12 Lingo, Ekos arm, Dynavector IVX, Linto phono stage, Resolution Audio Quark speakers for mid and upper range (small UK brand), separately enclosed bass speaker. CJ DF2 CD player; CJ PV12, active cross-overs - CJ 55 on midrange / treble, Trilogy tube amp for separate bass speaker.

A You are experiencing turntable rumble, and the drivers are moving due to very low frequencies, perhaps at 5 Hz - 10 Hz. You should insert a rumble filter in between your preamplifier and power amplifiers, and perhaps you can do it by modifying or adjusting your active crossovers. It should be used to remove everything below about 20 Hz.

Q I will soon be making the upgrade from receiver to separates and am not quite sure how to proceed. The folks at Bag End tell me that for my sub to operate optimally, I need to send a full range signal from the processor to the sub. If I use 3 interconnects from the L,C,R pre-outs to the line level inputs on the sub and another 3 interconnects from the sub's high pass outputs (95 Hz) to an amplifier, it could potentially be expensive and may produce other complications such as noise. If I wish to use the subwoofer out option, many processors will not permit me to send a full range signal to the sub, since they will use their low-pass filter. I am not sure how the Bag End was configured in your review.

My current speakers are PSB Century 400s (60 Hz -20 kHz) in front, Stratus C6 (45 Hz -21 kHz) center, and Sonance TR3000s (40 Hz -20 kHz) mounted in the ceiling as surrounds. I am very happy with the choices I have made so far with your advice, and would like to continue to make informed choices (and seamless integration) as I move to separates. Processors under consideration at present include the Sony TA-E9000ES, the Acurus ACT-3 and the B&K Reference 20, although I am obviously open to suggestions.

A I would recommend just using the subwoofer output from the processor. There will be resulting phase shift, and the Bag End does not use a conventional low pass crossover, nor does it have adjustable low pass frequencies, so you might have to use the phase switch or move the subwoofer to a different location. Hopefully, in one of the next generations of receivers and processors, we will be able to select the low pass to the subwoofer and high pass to the other channels with digital processing (choice of 40 Hz to 100 Hz or so, with several settings along this range). By using digital processing to do it, phase shift can be avoided.

Q Now that I have a good home theater system, I have found that I am disappointed in the movies. The old ones have better stories, but they are black and white with no surround sound. Even the modern ones are often boring. Do you think I am just getting accustomed to having a theater in my home?

A Well, I think that it is a combination of things. Films have become very expensive to make, and many movies are really just fast food cinema. Special effects and digital graphics have become the central theme rather than stories about people. It's rather irritating to spend $7.50 for a ticket and then be disappointed. We should demand more for the prices we are paying at the theater. Actually, I decided to try my hand at it and will be producing a motion picture. I have not finalized the script, but it may be one written by someone else, or even one based on my own book. You can see an idea I have in mind at http://www.sdinfo.com/dngoht/downgallows1.html, where I placed an introduction for a possible plot. I am negotiating with potential production companies now.

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