Q&A # 231 - May 22, 2001

Staff

Q The following components make-up the audio portion of my home theater system:

Front speakers: Definitive Tech BP-8B
Subwoofer: Sunfire Mk II
Receiver: Pioneer Elite VSX-07TX

The sub is fed directly from the sub pre-out of the receiver. My question is this: Should the front mains be configured as "Large" or "Small" and what would be the crossover range setting on the sub?

A This model has two 5 1/2" woofers, so configure them as "Large" and set your low-pass crossover in the subwoofer to 50 Hz.

Q I purchased a Yamaha receiver capable of decoding DTS and DD, but is there any way to upgrade to DTS-ES or DD-ES without buying a new receiver?

A The correct terminology is THX-EX and DTS-ES. Both are 6.1 formats, with 5.1 of them being discrete (like DD and DTS), and the seventh channel (center rear) being a matrix derivation from the rear channels (matrixed like Pro Logic). Just as a further reminder, DTS Discrete 6.1 is not matrixed for the seventh channel (center rear). Rather, that center rear channel is discrete just like the other 5.1 channels. DTS Neo:6 and Pro Logic II are matrixed 5.1 channels derived from two stereo channels, just as Pro Logic is, but they produce stereo in the rear.

OK, now that we have the terminology straight, all you need to derive that center rear channel from your 5.1 system is to take the pre-outs from the rear left/right and pass them into an old Pro Logic receiver. Leave all your speaker connections from the DD receiver as is. Connect the center channel output from that old receiver to the rear center speaker, and you are in business. If you want to be a purist, replace the rear left right speaker connections that were connected to your DD receiver with the front left/right speaker outputs from the Pro Logic receiver. This way, info to the rear center won't be duplicated in the rear left/right.

Q I was wondering if you could help me? I have a number of components that I'm trying to connect to obtain the best home theater sound. However it just doesn't seem to be working right. When I watch programs in Dolby Surround (or any surround sound broadcast), I get hardly any sound from my rear speakers. I believe I do not have it hooked up correctly. Is there a guide I can obtain to hook up components of different manufacturers?

A Broadcast TV programs have the problem of maintaining proper phase relationships between the two stereo channels that the rear channel is derived from when decoded. As the program passes from broadcaster to satellite to your TV, the phase can get out of alignment, and this results in poor decoding. Secondly, I have noticed that the stereo signal in some broadcasts seems to be partially blended, meaning that there is less separation between the channels. Again, this will affect Pro Logic decoding in a detrimental way. This is one problem that Dolby Digital does not have. In the meantime, we just have to put up with the fact that conventional broadcast programs in Pro Logic or Surround Sound, will not decode very well.

Q Last November, I purchased a Sony WEGA KV27FV16 color TV. I was hoping to keep the TV around for at least another 3 to 4 years, until the cost of HD products comes down to earth. Would you be kind enough to recommend an appropriate DVD player? My understanding is that my TV would not take advantage of progressive scan capability. My preference is not to spend a lot of money now (I know cost is relative) because the technology is rapidly evolving. I'd like to keep it below $300. Perhaps at that price range, it doesn't make much difference. In which case, I'll go with a low end Sony. Or does the quality of the TV merit a higher performance unit? I have some crazy idea that support for CD R/W is an important feature. I'm thinking that if I ever get around to creating CDs on my PC, I might be able to use the DVD player to listen to them. Sony doesn't support this. Do you have any inside scoop that they will shortly? Or am I placing too much importance on this feature?

A For $300, you can now get DVD players that output progressive component video. CD-RW playing capability is also becoming more common. It is really just all in the chips, and they are very inexpensive. The Apex AD-800 DVD Player does all of the above, for $229. We are testing it in our second Benchmark Event, in two weeks.

Q I have seen some initial description of using two additional ceiling speakers (in the mid-room area) to augment a 7.1 setup (5.1 with two additional speakers from synthesized signals), and then possibly two more ceiling speakers to give a 9.1 setup. I understand that this "9.1" arrangement might have gained more attention if commercial theater owners hadn't rebelled against the added cost. Many writers (THX enthusiasts?) have supported the use of dipoles for the side surrounds, and perhaps direct radiating speakers for the rear surrounds. What type of speakers are suggested for the ceiling pair in the middle of the room? (I happen to have a pair of speakers in such a location and was wondering if I could make use of them.)

A I'm not all that crazy about in-walls in general, but if done well, you can get pretty acceptable results. Ceiling speakers have yet to win me over for anything other than background music. If you were going to use ceiling speakers for side channels, I would go with dipoles with each radiating "pole" facing forward and backward respectively. The problem with ceiling speakers isn't in the speakers themselves, but because the speaker must be pointing down. This pretty much guarantees that you're not going to get very accurate reproduction unless they're more or less on top of you.  Also, the closer you get horizontally, the more they dominate the balance, which causes the balance to shift towards the closer speaker. Dipoles used ala THX will generate virtually no direct sound, because of the cancellation of the out-of-phase radiation, and therefore will not suffer the listener such a plight so long as the listener remains in the null. They also can't lock down a definite position, but that's somewhat a matter of taste.

A more conventional speaker, or for that matter, an in-wall speaker, can be mounted a few feet above the listeners' heads, so that the main direction of the transducers is aimed over the listeners. The benefit of such an arrangement, aside from offering the potential for directionality, is that listeners who sit closer to the speakers, and therefore more under the speakers, are more off-axis for that speaker and more on-axis for the speaker that's farther away. It's not a perfect fix, as the frequency response will deviate a little, and the time-alignment is only really dead on for one spot anyway, but it makes the shift of balance more stable, gradual, and less distracting.

Q I'm suffering from a bout of insomnia and having a time delayed discussion on an audio forum (the Audio Asylum to be exact) on PCM vs. DSD (Direct Stream Digital, used by Sony in SACD). Taking for example DSD vs Redbook CD: 64 samples of DSD occur in the time of one Redbook PCM sample. Bit Score: DSD 64, PCM 16 (huge advantage for DSD). At medium Res (24bit/88.2KHz for easy math): 32 samples of DSD occur in the time of one PCM sample. Bit Score: DSD 32, PCM 24 (approaching parity). At high Res (24bit/176.4KHz): 16 samples of DSD occur in the time of one PCM sample. Bit Score: DSD 16, PCM 24 (PCM wins this one).  Is there any merit to this line of thought, or is this just the ramblings of a person that can't sleep?


A The absolute number of samples is not necessarily the criterion to judge quality. For instance, if there isn't any content above 20 kHz, it's very likely that the higher data rate required for 24 bit, say 176.4 kHz sampling, will mean no greater performance when constructing the waveform, than if it were running at 88.2 kHz, or what have you, because of the very simple Nyquist theorem. If you look at MLP characteristics, you can see that you can increase compression rates by simply low-pass filtering the analog signal before A/D conversion, or for that matter, after it, so long as it is done before encoding. And, if you look at upsampling, or for that matter, oversampling, they both result in a higher bit rate when it gets to the D/A section, but the actual resolution is identical, and the higher sample rate in both cases exists EXCLUSIVELY for the sake of applying digital filters which must operate within the constraints of the Nyquist theorem.

It kind of runs along the argument that one 5.1 format is superior to another because the data rate required to pass along the compressed audio data is higher, ignoring the fact that they use entirely different compression algorithms.

What DSD does do pretty well is allow very simple DACs to be used. Essentially, you feed the data stream through a low-pass filter and maybe some analog amps and you're done!

Q How would you best describe the term "lobing" when applied to speakers? Is it the "interference" of one driver's sound with another's?

A Yes. I would only add that the interference is caused by some sort of delay between the radiation of each driver, due to a combination of location in relation to each other, the direction of the listener as it relates to those locations, and phase shifts caused by the crossover network, all of which contribute to the end result. But, yeah, dead on dude!

Q I have a 38" Sony WEGA TV set, a Sony Trilogic HiFi VCR and a connection to Sky Satellite TV Service. I intend to buy a S-VHS recorder  to record the satellite programs with a better quality than VHS. The problem is that the TV has S-Video inputs, but the satellite receiver (Philips) has no S-Video outputs. Will I get better recordings than the ones I get today even if I connect the satellite receiver to the S-VHS recorder using the standard (red, white, yellow RCA) connectors, and the S-VHS recorder to the TV with S-Video connectors?

A Yes, you will still get better quality with the S-VHS recorder than using a regular VHS recorder, because satellite TV has resolution similar to the S-VHS recorder (higher resolution than VHS). The high resolution images will pass through the RCA cable (composite video) alright, but it will have less color clarity than if you used S-Video all the way.

� Copyright 2001 Secrets of Home Theater & High Fidelity
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