| Home | Audio mag. | Stereo Review mag. | High Fidelity mag. | AE/AA mag.
Departments | Features | ADs | Equipment | Music/Recordings | History |
|
DMX: Info, Pros, Cons Dear Editor: In one of his last "Behind the Scenes" columns for Audio, entitled "Classical Derailed" (May), the late Bert Whyte sang the praises of a listening source for classical music called Digital Music Express (DMX), owned by International Cablecasting Technologies (ICT). Could you please give me a mailing address or phone number for ICT so that I can learn more about this system and its availability in my area? --Rossney E. Smyth Chester, N.J. The Editor-in-Chief's Reply: Contact ICT at 11400 West Olympic Blvd., Suite 1100, Los Angeles, Cal. 90064. You can call ICT at (310) 444-1744. -E.P. Dear Editor: I read Bert Whyte's "Classical Derailed" with great interest. Readers may be interested to know that DMX is offering a new service this year. The problem with the standard DMX system is that it is tied to cable. The new service is available via DBS as well as cable. DMX for Business, as its name implies, is initially being offered to businesses needing background music, but it is my understanding that it will eventually be available to audio buffs. The system broadcasts 61 stereo pairs of audio channels (90 by early 1995, and 120 by year's end) via a single transponder on the new Telstar 402 satellite, on its Ku Band side. Required to receive the DBS broadcasts are a satellite dish (2 to 3 feet in diameter), an LNB, and a satellite receiver (made by ComStream). The method used for encoding the broadcasts is the two-channel version of Dolby AC-3. The receiver uses a "smart card" for system security. Telstar 402 was a good choice for the satellite, as customers may use the same dish and LNB (with a standard receiver) to receive all four PBS networks. The prospect is an exciting one for audiophiles, but I would miss hearing the added fare that only an excellent radio station can offer (news, interviews with artists, etc.). I hope, as systems like DMX and its descendants mature, programmers for the same will add the human element again-minus the commercials. Bard-Alan Finlan, San Marcos, Cal. Dear Editor: I enjoyed Bert Whyte's column about the joys of DMX, as well as John Gatski's article on "Digital Radio" (September). I'm one of the lucky ones who has DMX available through a cable system. However, in spite of its superb quality, freedom from commercials, and very reasonable price, I have elected to pass over DMX and continue to listen to the local classical music station. KING-FM has a big advantage that DMX lacks--a schedule. With DMX, you have no idea of what's coming up (or, for that matter, what you just missed), and the company has no intention of ever telling you. What you get from DMX, for all practical purposes, is sonic wallpaper. Although it would be duck soup, technically, to allow you to scroll through coming attractions, the company has assured me that this will never happen. Do you think I'm being overly critical? Ask yourself how much television would be worth if you had no way of knowing what was to be broadcast or when, if all you knew was that the program would be a drama, a sports event, whatever. How much would you pay for a concert ticket if you knew only that it would be for chamber music? The concert could start at any time, there would be no program, and the group would not be known in advance. I think I know why DMX has this policy. The company doesn't want anyone recording the broadcast. Unfortunately, this doesn't help the listeners. I have to choose how I will spend my time; listening to un known music is not going to be one of the ways. Norm Strong, Seattle, Wash. The Editor-in-Chief's Reply: I agree with you to some extent, though I find my own music listening via radio to be of the back ground music type. However, it seems to me that the concert is constantly going, as opposed to one that starts at a certain time, a time that always seems to be inconvenient to me. While I don't have a printed program, there is one, being played by a first-rate pick-up group, as it were. As far as I can see, the "no-recording" policy isn't really DMX's but rather that of the record industry, which might well have crushed the fledgling effort otherwise. In the end, then, isn't the quality of this service enough reason to buy it? While you must make your own decision, it appears to me that the service will be commercially viable. -E.P. Pesky Power Lines Dear Editor: I sincerely enjoyed Edward M. Long's article "That Mysterious Source: The A.C. Power Line" (June). It was very informative and did spur my interest in how power affects the quality of my audio system. However, I was wondering if you are considering a follow-up article giving specific suggestions for those who wish to improve the power supplied to their audio system. Or if you are considering a "round up" article, similar to the home/car directories, itemizing the various types and pieces of equipment available to handle the a.c. power problem (with specifications, manufacturers' addresses, etc.) and exploring the differences between power-line "conditioners" (equipment that maintains an a.c. voltage) and power-line "filters" (equipment that merely filters r.f.i./e.m.i.). Are home computer conditioners good enough for high-end audio equipment? I do have one specific question. I have received information from one manufacturer of power-line filters, and test results show that their filters begin to attenuate r.f.i./e.m.i. at 10 kHz at 15 dB, whereas other power-line filters begin to attenuate at 60 kHz at 3 dB. Can you elaborate on the relationship between frequency and the amount of attenuation? Bryan X. Sherrod, Pleasant Hill, Cal. Author's Reply: Thanks for your kind words about my article. I appreciate it greatly when readers write and tell me that I have stimulated their interest. I'll answer your specific question first: It would appear that the manufacturer you mention is serious enough about suppressing r.f.i./e.m.i. that they use more expensive, larger value components (chokes and/or capacitors) to do a better-than-average job. If their power-line filter attenuates 15 dB at 10 kHz, then it certainly will do a good job at higher frequencies. A filter that attenuates only 3 dB at 60 kHz will have a very steep slope to suppress r.f. energy one octave higher at 600 kHz, which is near the low end of the AM radio band. My guess would be that a power-line filter will not have this kind of steep slope filter. It would be interesting to look at the wide range of a.c. power-line interface de vices that are available and list their attributes. There are many such devices, from simple, inexpensive surge suppressors to complex, expensive a.c. line conditioners. The simplest device does offer some ad vantage over just plugging your system into an a.c. wall outlet. An a.c. power-line conditioner that offers a truly isolated inter face, large power capability, and uninterrupted power can be very expensive. For a life-support system, this is an absolute necessity; for an audio system, it might be fun to play soothing music during a local disaster that knocks out everyone's a.c. power. A good compromise, for audio systems that don't need uninterrupted a.c. power, is a device like the Panamax Max 1000 surge protector and line conditioner, which I reported on in the June 1993 issue. If there seems to be enough interest, I am sure that our esteemed editor will consider a round-up article. -E.M.L. Dear Editor: I read with much interest Edward M. Long's article in which he discussed the effect of a.c. power lines on audio equipment performance. I would greatly appreciate it if he would recommend to me any articles that deal with methods to insure proper PC quality, beyond what he mentioned in his article. I am interested not only in how I can improve my existing installation but also what specs I can give my electrical contractor for new construction. Alex Wallau, Vice-President, ABC TV Network Group New York, N.Y. Author's Reply: The best information about a.c. power-line problems is the Handbook of Power Signatures by Alexander McEachem, published by Basic Measuring Instruments, 335 Lakeside Dr., Foster City, Cal. 94404. The phone number is (415) 570 5355, and the FAX number is (415) 574 2176. This handbook is very technical and shows many problem waveforms along with possible reasons for them. I hope you will find it helpful.-E.M.L. Praise for Sony's Portable DAT Dear Editor: I have owned a Sony TCD-D7 portable DAT recorder ("Equipment Profile," June) for about three months now, and I am very impressed with its performance. The unit is tough! I connected it to my old truck's stereo system via a cassette adaptor (same type as used for portable CD players), and it sits on the seat beside me. Several times when I made fast stops, the TCD-D7 slid off the seat and bounced on the floor, with out stopping or even muting! One time I made a fast left turn; the unit fell on the floor, skidded across, and slammed into the right door-and didn't skip a note! Another extremely useful feature is the switchable "AVLS." Sony touts it as keeping volume at safe levels when listening with earphones, but its real use is to reduce dynamic range for listening in a car or noisy truck. I have found, to my dismay, that I usually can't listen to uncompressed music in the truck with the windows down; the music is either too soft or blasting me out! This happens with pop hits from 45-rpm records! I'd hate to think what classical music would do if not compressed. The TCD-D7 has output volumes from 1 to 20; the compressor kicks in at about level 6. The higher you set the volume, the more compression there is. By the time you get up to 14, the music has no dynamic range at all. Any higher, and the bass tends to modulate the treble. At about 9, the music sounds like that from a typical FM station. The unit has a switchable auto level control for recording music and for recording from the mike input. I don't use the feature, since I want to get full dynamic range on the tape, but I guess it would be useful for recording conferences (if you wanted to use such a good recorder for that). Another useful feature is the removable battery holder. It's possible to take the holder out, change the batteries, and re place it while driving on country roads, al though you do have to slow down some. The only gripe I have is that the unit does not have a standard optical or digital input. [Special cables, at $60 to $80, are required. -I.B.] Finally, I don't see why anyone would buy a digital recording medium that uses data compression. Any failure in the recording medium over time could cause the loss of too much data for reconstruction by the logic system. DAT uses the most data to record the music and thus should be most able to compensate for dropouts or other problems. I once creased and crumpled the tape in a DAT cassette (by mistake), and the machine still played it! I would recommend the Sony unit to anyone who wants digital quality sound on the road. The tapes are cheap, and they play for a long time. P. V Brown, Woodbine, Md. Equipment Help Wanted Dear Editor: I've owned an FME open-reel tape recorder, Model 47A (see illustration), since 1969. I'm trying to find parts and/or another unit, whether it's working or not. I would appreciate hearing from any individual or organization that collects these 1950s recorders. Kevin Wheeler, 3907 Sunbeam Ave. Chattanooga, Tenn. 37411 Dear Editor: My SAE amplifier, Model 2400L, only functions on one channel. Local repair shops have tested the amp but are unable to repair it because I no longer have a schematic, nor a parts list. Since SAE is out of business, the shops are unable to get any further information. Also, my SAE tuner, the Mark VIII, has non-operational LEDs, making it very difficult to determine the stations. This is excellent equipment that I have enjoyed for many years. I am disappointed that I have not been able to repair the units and would appreciate any suggestions. Bruce Raiffe, P.O. Box 821 Edison, N.J. 08818. (Audio magazine, 11/1994) = = = = |
Prev. | Next |