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Surround sound with VHS

Old 07-04-02, 01:59 AM
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Surround sound with VHS

I have a Panasonic 5.1 HT. I was just wondering how you get a VHS tape to have surround sound. I have tried using the super surround feature, but there seems to be alot of static on my rear surrounds. Is there a certain way you set up your speakers to emulater surround sound?
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Old 07-04-02, 03:44 AM
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I believe the tape has to have a surround sound track on it to give you surround sound.

Do the tapes you've tried this with say Dolby Pro Logic or Dolby Surround on them? Or just stereo?

-David
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Old 07-04-02, 03:53 AM
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The main thing you need is a hi-fi VCR, connected to your Dolby Pro-Logic-capable receiver with left and right RCA cables. Any pre-recorded video tape with the Dolby Surround logo on it (which is virtually all of them these days) will decode in surround. Also, using the VCR's tuner to watch TV with, any TV show broadcast in surround will also be decoded in surround.
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Old 07-04-02, 10:24 AM
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Thanks, guys. I just tried it with the Dolby Pro Logic option, and it works pretty good.

Much to learn, I still have.
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Old 07-04-02, 12:10 PM
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It's really good on some movies, most notably the VHS of MIB, I thought. Be warned though, that as the video quality diminishes, so does the audio! What may not sound bad through the TV may come out fairly bad through the receiver.
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Old 07-04-02, 12:57 PM
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Prologic can do weird things to tapes that are stereo only, so keep that in mind, too. I once watched a tape on my old prologic system and the dialog came out of the rear channel. Weird.

But yeah, when the tape's good, it sounds all right.
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Old 07-04-02, 05:02 PM
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Here is a liitle primer on how pro-logic is encoded and decoded. It is a 5 channel format that was designed to give an approximation of theater style surround but be able to be encoded on the analog two track (stereo) audio portion of a VCR tape. The 5 tracks, as most people know, are left, center, right, left surround and right surround. Your stereo VCR has just the two: left and right. The method that Dolby came up with has the left and right channel information recorded as they normally would.

The center channel information is sent to both left and right simultaneously. The main reason for this is in mixing the final soundtrack for the movie, the center channel is almost always given just as much consideration as left and right. If this information is not provided for someone who does not have surround sound, a whole lot of the audio information would be missed. The left and right surround is actually what is referred to as a split mono signal. It is technically one channel of information that is sent to two speakers. The signal is recorded equally on both sides (left and right), just like the center channel, except it is done at a very miniscule delay. This delay in the time domain we are talking about here is referred to as phasing. Phasing for audio applications is measured on a 1-360 degree scale like a circle. When a signal is out of phase 180 degrees with itself it cancels itself out. Hence when you listen to a pro-logic sound track in stereo the left, center and right information is there but the surround is not.

When this two channel audio hits your receiver the pro-logic decoder sorts it out and sends it on its appropiately merry way. When it sees left channel information only it goes to the left channel. Same with the right. When it sees identical information on both channels (but in phase with itself), it goes to the center channel. And when it sees identical information on both sides but out of phase with itself, it goes to the left and right surround.

As far as how much information is in each channel, that is up to the people making the movie. Which is why there is often a dramatic difference in what is on each channel from movie to movie.

As you can imagine, knowing the encoding process now, timing problems that can happen with audio on videocassette, from stretching of the tape to alignment issues at the heads of the VCR, will cause wierd things to happen audio-wise over time.

Last edited by macsax; 07-04-02 at 05:09 PM.
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Old 07-04-02, 07:39 PM
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Originally posted by macsax
Here is a liitle primer on how pro-logic is encoded and decoded. It is a 5 channel format that was designed to give an approximation of theater style surround but be able to be encoded on the analog two track (stereo) audio portion of a VCR tape. The 5 tracks, as most people know, are left, center, right, left surround and right surround.
This is wrong. Dolby Pro-Logic is a four-channel format, not five. The rear channel is a single, monophonic channel. In most set-ups, it's sent to two speakers, but the signal going to each speaker is the same.
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Old 07-05-02, 06:28 AM
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Wow! I appreciate all the info, guys. I only bought my Home Theater a few weeks ago, and I haven't bought VHS tapes for several years, so I didn't even know such a thing as Pro Logic existed on a VHS tape. Looking through my old tapes, I now see that about half of them have the Dolby Surround logo on it. Kewl.
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Old 07-05-02, 04:29 PM
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I see your living up to your name Mr. Salty. If you would have bothered to read the entire post you would have seen that I explained that. Don't be so hasty with critical judgement. What makes it a five channel format is in the end you have five channels of amplification.

Last edited by macsax; 07-05-02 at 04:32 PM.
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Old 07-05-02, 05:09 PM
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Originally posted by macsax
I see your living up to your name Mr. Salty. If you would have bothered to read the entire post you would have seen that I explained that. Don't be so hasty with critical judgement. What makes it a five channel format is in the end you have five channels of amplification.
I'm sorry, but where in my post did I write anything that would justify you getting personal? Cool your jets a little.

The fact remains that calling Pro-Logic a five-channel format is still wrong, even though your description of the process was correct. Look at the back of the case of a Pro-Logic-encoded DVD. It will read Dolby 4.0.
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Old 07-05-02, 05:23 PM
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Originally posted by macsax
The left and right surround is actually what is referred to as a split mono signal. It is technically one channel of information that is sent to two speakers. The signal is recorded equally on both sides (left and right), just like the center channel, except it is done at a very miniscule delay. This delay in the time domain we are talking about here is referred to as phasing.
That isn't true at all. Dolby Pro-Logic has a straight mono surround channel without phasing. What you have described is THX Cinema Re-EQ processing. This is available only on THX-certified receivers. A standard Dolby Pro-Logic decoder does not add a time delay between the right surround and left surround channels.

Edit to add: Actually, now that I think of it, you may be talking about Dolby Pro-Logic 2, which is again not the same thing as standard Dolby Pro-Logic, and has only started showing up on surround receivers in the past year or so.

Last edited by Josh Z; 07-05-02 at 05:25 PM.
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Old 07-06-02, 01:41 AM
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Josh...please don't mis-understand the description. The phasing process is how the mono rear channel information is encoded onto the two-channel format. In the decoding process on the receiver end the phase is corrected before playback.
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Old 07-07-02, 04:00 AM
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Sorry things jumped the track a bit here Quadinaros. For clarification purposes, Pro-Logic is a 4 channel mix encoded to 2 channel stereo, then decoded and most commonly sent to five output channels.

To take the rear channel encoding point home, here it is straight from the horse's mouth. From an article titled:Dolby Surround Pro Logic Decoder Principles of Operation by Roger Dressler, on the Dolby website at www.dolby.com

The L and R inputs go straight to the Lt and Rt outputs without modification. The C input is divided equally to Lt and Rt with a 3 dB level reduction (to maintain constant acoustic power in the mix). The S input is also divided equally between Lt and Rt, but it first undergoes three additional processing steps:


* Frequency bandlimiting from 100 Hz to 7 kHz.
* Encoding with a modified form of Dolby B-type noise reduction.
* Plus and minus 90-degree phase shifts are applied to create a 180 degree phase differential between the signal components feeding Lt and Rt.
I originally received my information from a Dolby representative several years ago and the above listed article goes into even more detail. If you are interested, it is very informative. There is also a wealth of other knowledge on Dolby technologies. So if you are a gadget geek or a techie it is worth checking out if you haven't already

I apologize for any initial confusion.

-Shawn
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Old 07-07-02, 01:16 PM
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I think I got it. I've tested a few of my tapes with this and it works pretty well. Thanks again for all the feedback.
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Old 07-08-02, 11:09 AM
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Originally posted by macsax
Sorry things jumped the track a bit here Quadinaros. For clarification purposes, Pro-Logic is a 4 channel mix encoded to 2 channel stereo, then decoded and most commonly sent to five output channels.
I think the simple problem is the misuse of terminology. "Speakers" and "channels" are not synonymous, since a channel is unique stream of data, and a speaker is a physical item you can hang on your wall. Pro-Logic does not have 5 channels, although the soundtrack is typically sent to 5 speakers.

I think we're all on the same page here.

Last edited by DigIt; 07-08-02 at 11:11 AM.
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