Q&A # 175 - April 27, 2000

Staff

Q When testing the frequency and volume responses to your subwoofers, how do you set the subs as a baseline? As an example, are they calibrated to a set volume such as with the AVIA calibration disc at 85 dB and then measured from that point? The reason I'm asking is that I have a Velodyne VA1012X and note that in my room with sub calibrated to 85 dB, it goes to 90 dB at 35 Hz and 80 dB at 25 Hz. I am trying to determine if I would be better served with a Paradigm PW2200 or similar sub as opposed to what I already have. My main concern is that I don't "feel" the explosions like others mention and I'm wondering if it is because the sub doesn't output loud enough or move enough air at the lower frequencies.

A The baseline is usually 90 dB at 20 Hz or 25 Hz, and then the other frequencies are measured, leaving the controls on the subwoofer where they are. This includes the crossover (low-pass) at its highest setting. The measurement results will include not only the output of the subwoofer but the effects that the room have, which usually means a couple of peaks and valleys. There is no way to get around that unless an anechoic chamber is available. The VA1012 is a good subwoofer, but if you want more intensity, a larger sub is in order. I would suggest something with a 15" or 18" driver and plenty of amplifier power.

Q Some DVDs do not indicate a PCM recording but say that they have a 5.1 DD track and a separate Dolby Stereo track Will the PCM track light up only when there is a non-compressed PCM bitstream feeding it? If all the tracks are DD-encoded, then why not just supply the 5.1 track and let the DVD player downmix it to two-channel stereo?

A Many of the Sony DVD titles contain an uncompressed PCM track. It is usually on Audio 1 with the 5.1 track being on Audio 2. You ask why not just provide the 5.1 and let the decoder downmix. Because you are throwing away information by compressing it (downmixing it). I have found that the two-channel PCM track is MUCH better than the compressed Dolby Digital track on music DVDs. I am also able to upsample the PCM track to 24/96, getting a further improvement. You cannot upsample a Dolby Digital signal, because too much has been thrown away already for the upsampling to work properly. It is sometimes hard to tell because DVDs are so poorly labeled. You can look at web sites like http://www.dvdexpress.com and http://www.dvdempire.com to see what tracks are listed.

Q I am considering the Dwin TransScanner. Will a progressive DVD player offer a better picture than a normal DVD player going through the Transcanner? If so, do I just stick with the DVD player I already have? If not, will Dwin have a software upgrade or something that will allow a progressive player to be used with the Transcanner?

A The Dwin TranScanner cannot accept a progressive signal. A progressive DVD player only outputs 480p, so, depending on screen size and aspect ratio, you will need to feed the TV 720p (16x9) or 768p (4:3).

Q I'm looking into buying a receiver to start building my home theater one piece at a time, but I've heard a lot of confusing terminology out there, some that I understand and some that I don't. What is S-Video switching? I have a DVD player in which I'm running composite video, but I'm also looking into buying a new TV, and I heard that component video inputs (RGB) are better than S-Video. Any help would be very greatly appreciated.

A When a receiver says that it has S-Video switching, it means that you can plug in various sources like DSS, DVD, and LD into the receiver via S-Video cables. Then, you can run just one S-Video cable from the receiver's S-Video output jack to your TV. When you select a specific source like DVD, it will route the video coming from the DVD player to the TV. The biggest jump in performance comes when you go from Composite to S-Video. There is an improvement when you go from S-Video to component, but it's not as easy to see. It becomes easier, the bigger the display you have. You get deeper saturated colors that contain less noise in them. The NTSC decoder is also bypassed. Some of the new receivers have component video switching, and some TVs now have component video inputs. But, as I mentioned, you will notice the largest improvement in using S-Video rather than composite video.

Q Are movies that are encoded in Dolby Surround for VHS always transmitted over cable television in Dolby Surround? I recently purchased a DD/DTS surround sound system, and I am certain that everything is connected properly. I do not have a TV cable box. The coaxial cable carrying the cable TV signal is connected directly into my 36" Sony Vega stereo television. I have watched several movies on non-premium cable channels, and the sound always seems to be hit or miss. As I understand it, Dolby Surround has to be encoded in a movie's two channel audio track to produce true Dolby Surround through a Pro Logic receiver. It seems like some of the movies which are encoded in Dolby Surround for VHS may be transmitted on cable TV in stereo rather than Dolby Surround. Please respond with any thoughts.

A It is possible for a cable company to broadcast a movie that is encoded in Dolby Surround (this means the surround sound is encoded in the two channels of the stereo sound). There are also numerous TV programs that use Dolby Surround, including "The Simpsons" and "The X-Files". Now whether or not your cable provider is doing that may a different story. So to answer your first question, no, not all movies that are encoded in Dolby Surround are transmitted that way by the cable companies. Your best bet is to call your local company and find out. Of course the people you speak with might not be able to answer that question either. Part of the problem is that phase relationships between the two channels in the stereo sound can get messed up in along their way to your TV. When the phase is out of alignment, Pro Logic can't decode them into surround sound. This is one of the many benefits of digital 5.1. The bits reach your home unchanged, and they decode into surround sound perfectly.

Q You stated in one of your Q&A responses, "In order for a DVD player to read a CD-R disc, it needs a second laser." I don't think this is correct. I have a second generation Panasonic player (A310), which I believe only has a single laser. I am able to play, without any problems, CDs burned from a Toshiba CD Recorder, even CD-RWs. In fact, I have never had a problem with CD-R playback in any machine (my car player, an ancient Sony Discman, etc.) I believe the most important aspect in making problem free CD-Rs for music playback is correct software (Adaptec Toast and Jam for the Macintosh are excellent) and good quality blank media.

A For a DVD player to read a CD-R, it needs a second laser or a method to change the wavelength of the laser. A CD-R uses a dye that does not reflect a DVD laser beam. A laser in a CD player is not the same that is in a DVD player, and this is why your car has no problems reading a CD-ROM. Toshiba has not released a DVD player yet that can read a CD-R. However, they do offer some DVD-ROMs that can read CD-Rs.

Q Which type of TVs are capable of handling the signal from a progressive scan DVD?

A You need a TV that can scan at a higher frequency. Consumer TVs scan at 15.75 kHz. A progressive scan DVD player requires a TV that scans at 31.5 kHz. Many new DTVs can accept a progressive DVD signal, but some will then upconvert that (480i) to 1080i. Toshiba makes MANY TVs that can do this. The TW40X81 is one we recently reviewed that plays progressive DVD, and it is also one of the most affordable DTVs on the market.

Q I bought a second hand Parasound HCA 2200 Ultra High Current power amplifier and connected it to my Yamaha RX-V 2095 driving the main front channels. I have an NHT speaker system, a pair of 2.5i in front, Audio Centre one, and surround zeros for the surrounds. I am really happy with the complete system on theater applications, but I am having a slight humming sound (similar to the humming sound coming from a fluorescent lamp transformer) coming from the front main speaker while using the system on two channel setup. The humming sound is more audible when it is quiet at night and when there is no music or audio signal being received by the power amp. If I get a dedicated AC power line for the Parasound, will the humming sound disappear?

A This sounds like a ground loop problem, or perhaps the interconnects from your Yamaha to the Parasound are too close to the AC power cords. Try moving the interconnects around. Also try disconnecting things one at a time to see when the humming disappears. When you find it, that is the connection to work on to solve your problem.

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