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Q&A # 177 - May 12, 2000

Staff

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Q I recently read your article detailing the LFE channel in Dolby Digital and found it one of the more understandable articles about the subject that I have seen. I have a question about proper channel sound level calibration. I have both AVIA and Video Essentials (VE) and note a rather significant variation between the two when setting speaker levels to 75 dB. Why is this? Also, what would be the proper levels to set the channels to using VE (75 dB mains and ? for the sub)? I have a Velodyne VA 1012X sub and frankly have never been able to experience the oomph with it that I find in the theater. I have found that with the sub firing lengthwise into my rectangular room, I notice more "feel" when I'm in the doorway at the other end as opposed to right next to the unit. Unfortunately my room is set up to where the entertainment center and the seating areas are along the long walls facing each other. I'm wondering if the short distance is somehow not allowing the wave form to actually fully form and thus it won't make any difference what type or size of subwoofer I have. I would appreciate any insight you could offer into my situation.

A Thank you for your kind comments about the essay. We always appreciate feedback. You are correct in that , as I mentioned in the footnotes, the calibration sounds of AVIA and VE are different in level. Similar to the pink-noise used in cinemas, the test sounds on the AVIA disc are recorded 20 dB below the maximum allowable signal level. The pink noise on the VE DVD is produced lower in level. Unfortunately they were less participatory, so I don't have their specifics. My best educated guess is that unlike AVIA, their pink noise is recorded at 30 dB below peak. Neither one is right or wrong. It simply means that if one wants to locate the position of the volume knob that corresponds to the 'reference' level I brushed on in the essay, different setup levels would be used. Playing the AVIA pink noise at 85 dB and the VE signals at 75 dB should result in pretty much the same position of your volume knob. (And a very loud position that will be! Please be careful with your hearing.) Note that regardless of which DVD you use, the level that you balance your speakers at is of little importance. What is important is that they are all balanced to one another. To answer your second question about your subwoofer level, again the actual level you use is not important: Your only goal is to make that deep rumble equal in level to the pink noise from a main speaker. AVIA and VE approach this differently (I may do an addendum to the essay explaining why), but without going into that, your basic goal and consequently your subwoofer setting, will be pretty much the same when you balance it using either. Lastly, subwoofer placement is alas one of experimentation. I say 'alas' because the darn things are so heavy. Even with thousands of dollars worth of RTA and MLSS equipment, someone still has to move the big brutes around to find the perfect spot. Experiment aggressively. Try every possible position in your room. You will probably get better bass with the sub farther away from you than nearby, and I suggest starting by putting the sub near that doorway where you got such a good sound.

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Q In an effort to accommodate my wife, I'm looking for in ceiling surround speakers for my theater. They have to be of audiophile quality, as my system is Proceed/Krell/Vienna Acoustics. I have a pair of B&W 7se's in my dining room walls and love them, but would like to have a less 'directional' speaker to enhance the surround effect. Any recommendations? Also, how do you feel about an in-wall sub?

A There are many companies who make in-wall speakers. Here is a link http://www.speakerspecialist.com/inwall.htm. Personally, I don't like the idea of an in-wall subwoofer, because the location of the sub is important, and you won't know how well your choice of location is until you install it, and then it will be too late if you don't like the results. Also, the best subs are the really big ones (18") with more than a thousand watts of power. Something like that just won't go in the wall.

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Q We located the Radio Shack RF Modulator that some of your readers asked about a while back. It lets you plug your stereo audio and video signals from your DVD player into it, and it will then modulate the movie (video and sound) onto either channel 3 or 4, and outputs the signal to the antenna input on your old TV. That way, if you have an older TV with no external audio/video inputs, you can watch DVD movies. You should just use the video portion though, if you have a stereo receiver or digital surround receiver. Keep in mind this is just a temporary measure. It will result in loss of the superb video quality that your DVD player has, and the image will look like a conventional TV program, maybe worse. Get a new TV with S-Video inputs when you can do so. The Radio Shack modulator is item # 15-1244 and is $30. I use the Radio Shack RF modulator when traveling with my portable DVD player. This lets me plug it into most hotel TVs, as they don't usually have line-level inputs.  I thought I'd throw this in as another use of the RF mod. Now if they could make one a little smaller, with rounded edges, that'd be nice.

A Thanks for the info.

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Q I want to place banana plugs onto my speaker wire, and wanted to use the best method. Someone had told me that soldering (with silver solder) is the best way to prevent oxidation and loss of sound quality, but recently a salesman at a stereo store told me that crimping gets better surface contact and there is last chance of a faulty soldering job. So which is better, soldering banana plugs onto speaker wire or crimping them on?

A If you want the best connection, and don't mind making it rather permanent, solder the connections. However, it is very important that the solder joint is properly made. A good one looks very shiny, while a bad one looks dull. The problem with crimping is that the surfaces eventually oxidize and deteriorate the connection.

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Q I have a VCR tape of some things around the house with my kids. How can I edit music onto the tape without losing the video. I do not want the audio of the kids. I just want the audio from a CD that I have. Is this possible for me to do?

A Yes, and this is called "Dubbing". Most VCRs have this feature. However, I would suggest experimenting with a tape of something you don't want to keep. This way, your final procedure with the tape of your children will work right the first time.

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Q I am going to purchase a DVD player and have narrowed it down to the Toshiba SD-1200 and the SD-3109 (which I have been told is to be replaced by the SD-2200). My question is that since the 1200 has only a Toslink connection, while the 3109 has both Toslink and coaxial, is there a big difference between Toslink and coaxial?

A The two types of connection appear to function very similarly in quality, from what I can tell. Toslink (optical) cables are a little more expensive, but they work nicely when you have ground loop problems. Also, Toslink does not have an impedance problem, while coaxial can have such a problem if it is not 75 Ohms. Since receivers all have both Toslink and coaxial inputs these days, the 1200 should be fine, other than any features you might prefer to have on the 3109.

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Q You commented on the advantage/need of mega watts for subwoofers (this was in response to a Mirage 'digital' Subwoofer-1000watts). I understand some of the physics behind the need for power at these low frequencies, but I am curious about the utilization of all those watts. Specifically, I have two Passive Snell 550THX subs powered from a Parasound 1206THX amp. When I set the Gain control at the THX level, the sound is boomy and too loud. So, like many others, I utilize some of the test/set-up CDs & DVDs to balance the outputs of the subs and the other speakers. In so doing, the gain comes down about half way. Now the test tones at either 75 dB or 85 dB reference levels are balanced. So what happened to those Watts? I also have an older M&K MX-200 sub and sure enough I am turning the gain control half way down as well. So once again what happens to all the unused Watts? When the subs are turned all the way up, I can generate some pretty high SPL, but this is just for giggles & grins, because it sounds way too boomy. Not that it is crucial, but the Pre/Pro is a DSP A-1. What am I missing here? Is the gain control really just altering the manner in which the amp responds to an input signal . . . for lack of a better word, making it less sensitive, or more linear in response . . . sorta like the difference between the "9-o'clock setting on one preamp vs. the 9 o'clock setting on a different preamp? This is something I have noticed on higher quality preamps compared to the mid price preamps or receivers. This brings me to the dilemma of purchasing a Parasound 3500 amp at a great price . . . 350 watts @ 8 ohms and 500 watts @ 4 ohms. I was thinking I would use this beefy amp for the subwoofer, and reconfigure the 1206 for upcoming 7.1 setups. Is this over kill, and am I going off the deep end, falling victim to the Tooltime malady of more power, more power? Do I need to be saved from myself and told to relax a bit?

A Well, you might need to relax a bit, but you are on the right track with wanting plenty of power for your subwoofer. The boomy sound you are experiencing is more a factor of the driver's performance rather than the absolute amount of watts it is drawing. Especially if you configure it with the THX setting, this sends frequencies up around 90 Hz to the sub, and most sub drivers sound a little boomy at this frequency. As to the use of the watts, the power amplifier is capable of delivering x amount of them, but, depending on the volume setting, all of those watts are not required. It is like preparing dinner. There is plenty of food available for the cooking, but you don't cook more than you are going to eat. The unused watts don't go anywhere. They are simply not produced in the first place if the volume setting is low.

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Q I recently purchased a Toshiba 3109 DVD that also features HDCD decoding. I've noticed that some of the CDs in my library carry a label to the effect that they are recorded in "high definition 20-bit audio." However, when I put them in the new DVD player, the HDCD indicator doesn't light. It may be my imagination, but I seem to notice more of a quality difference between the old player and new on the disks that the Toshiba does recognize as HDCD. My question: is there a difference between HDCD and this mystery high definition 20-bit format? I assumed until now that they were one and the same.

A They are not one and the same. HDCD (High Definition Compatible Digital) is a technique used by Pacific Microsonics to get a 20 bit sound from a 16 bit CD. They record the sound at 20 bits and very high sampling rates, then downmix it to 16 bit/44.1 standard CD format, but include some codes that bring the sound closer to what it would be if it were being reproduced from a 20 bit CD. The other CDs you are referring to are marketing hype. Digital recordings these days are made with 24 bit/96 kHz recorders, or better. The CD producers are just telling you that the original recording tape is higher resolution than the final product, and this is likely better than if they had recorded it at 16/44.1 to begin with. Only CDs that specifically are encoded for HDCD will light up that HDCD LED on your player, and they will have an HDCD label on the CD jacket when you buy it.


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