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  1. Member
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    Wasn't sure which forum to post this in so thought I'd try here. I just purchased a great reciever for surround sound that includes prologic II which is great for my VCDs as it does a pretty good job of simulating surround from my stereo audio sources of VCDs. My question is this: When watching regular cable TV channels it seems that you get surround on some programs but others you don't. For instance watching sports events on TNT and TBS the surround is great and you really feel like your at the game, but when watching ESPN it seems like it's not in surround. I get just regular cable (not digital) and my TV says all channels are in stereo. Does the program have to be encoded in Prologic in order to get surround? I thought Prologic II automatically turns any stereo signal into surround, correct me if I'm wrong. Would like to hear from any prologic II users out there. BTW, a reciever with prologic II is a great investment if you have a lot of vcds or svcds. I bought a Panasonic for only $179, includes digital inputs, 3 S-video ins and one S-video out. Best purchase I've made in a while.
    Thanks,
    Tim
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  2. Member Cornucopia's Avatar
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    Timster:

    There are 3 Dolby Surround Matrixed-audio decoder types...
    • 1. Dolby Surround (the original) decodes to L,C,R, and S (1 rear only)
      2. Dolby ProLogic which also decodes to L,C,R, and S (1 rear); uses intelligent steering 4 better separation
      3. Dolby ProLogic II, decodes to L,C,R, and SL and SR; incl. best steering and separation

    There is only ONE Dolby Surround encoder, named oddly-enough "Dolby Surround".

    All Dolby surround-type decoders will decode any stereo signal. ALL. But just because it "decodes" it doesn't mean it does it correctly. A correctly encoded DS track has 2 channels, usually referred to as Lt and Rt. Decoders aren't smart enough that they can completely tell the difference between Lt/Rt and regular L/R. This may sometimes do nice things to regular stereo programming, but it certainly isn't what was intended. To make it clear, ProLogic NEVER actually turns regular stereo into surround, but it can surely GUESS and "synthesize" a type of surround.

    TV is another problem altogether. Broadcast and cablecast TV (analog) comes in on a coax RF cable. The RF signal of each channel includes a Frequency "muxing", if you will, of Video and Audio. It's split up something like this...
    • [Video Luminance-B/W]
      [Audio--Mono or StereoSUM]
      [Color Pilot BurstPhase Waveform]
      [Stereo Pilot Tone]
      [Audio--Stereo Difference]
      [Video Chrominance]

    If the Colorburst is garbled (in NTSC) you get ugly color. If missing, you get Black and White picture. If the stereo pilot tone is missing, you only get mono. If it's there when it's not supposed to, you either still get mono (if the difference signal is silent) or you get weird SH*#t when there is something impinging on that part of the RF spectrum.
    It's also possible that the station/channel is outputting everything to 2 channels, but don't have the correct playback decks or tapes to actually be stereo. Who knows! There are lots of variables here.
    I wonder what you mean by "your tv says all channels are stereo" 'cuz that's not true of just about every cable system. Digital cable has less of these confusing things, cuz there are flags in the data stream that signify the different parameters.

    Clear as mud, right?
    Scott
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    To give you a really short and clear, but much less detailed answer: Dolby Surround (which your Prologic decoder processes to give you center and back channels) has to be encoded in to the audio. Some TV broadcasts have it, some don't. If the show's audio wasn't encoded with surround sound you won't get any. If the signal is noisy (weak/bad TV signal, old worn-out VHS tape, etc.) your decoder might not be able to read surround encoding if it is there.
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    Thank you both for your informative answers. I'm wondering if a sportscast is live, it won't be encoded in dobly surround, and if it's a recorded event it might be? Who knows? As you say, there are a lot of variables. At least I know it's not a problem with my reciever. All my VCDs (MPEG2 via header trick) sound excellent as do just about any movie on TV. They were encoded with TMPGenc which must pass on the encoding information.
    Anyway, it was still a great purchase.
    Tim
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  5. Timster,

    First off go to www.dolby.com and read and read and read.

    Now to elaborate on what Cornucopia said
    Pro-logic's rear channel is mono meaning the same sound comes out of both rear speakers and is done by analog.The only reason it seems that the plane is going from the right front to the right rear is because your eyes and ears are paying attention to your right, the sound of the plane is also coming out of the left rear.

    Now pro-logic II is two rear channels and is done digitally.

    I have done a little research on pro-logic II .

    I started remodeling a room into a home theater and I was sick and then in an accident and by the time I re-coup-ed two newer models of my receiver came out.

    I thought about selling it brand new in the box never opened onkyo 787 so I could buy one with the new pro-logic II but was told it really wasn't worth it unless I was going to be watching a lot of older movies that were in stereo. Don't forget this is made to improve stero sound wether it is from old movie tv/cable or a cd.

    BTW- There is a great article about Pro-Logic II in Sound and vison's January issue. www.soundandvisionmag.com

    Hope this helps
    VCD4ME
    We were all NEWBIES once and the only stupid question is the one that's not asked?
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    Just another quick question on this subject. I tried about 4 different recievers before I settled on the one I have now. It seems that every reciever that has Dolby surround, the recievers will only let you adjust the tone controls of treble and bass when running in stereo mode. Whenever in dolby surround or DTS mode, you are not allowed to have control over bass and treble. Any reason why? It was the same on all 4 models. Do higher end units give you treble- bass control or is this just something about dolby. I must say I don't really need to change it as it sounds fine the way it is but I'm just curious.
    Tim
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  7. Timster wrote
    Whenever in dolby surround or DTS mode, you are not allowed to have control over bass and treble. Any reason why?
    I personally use an external eq and I do know that they say that you should not adjust anything when using any form of surround. I can't really explain the reason but don't forget when you are listening to a thx cerified receiver it is set up to meet standards.

    You should probably see if there is a good explanation online I doubt it will be on www.dolby.com seeing as DTS is a competitor of dolby digital, but there might be. The other thing you can do is go into a high end shop and they may be able to explain it further. There is a new "Home Theater for Dummies" book out you might check that out. If I can read one of my books again and explain it I will

    Hope This helps
    VCD4ME
    We were all NEWBIES once and the only stupid question is the one that's not asked?
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  8. Member Ste's Avatar
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    The Super Bowl was broadcast live, and it was in Dolby Digital.
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  9. To answer the original question, a Prologic amplifier will take _any_ stereo signal and create a more spacious sounding effect. Obviously the effect will be better if it's specifically mixed for Prologic at the source.

    However, a mono signal will sound _very_ mono because it will only come out of the centre channel.

    > my TV says all channels are in stereo

    Well, sort of. It sounds to me like the link between yourself and the TV station is in stereo, so the TV detects the presence of the stereo channel in the broadcast and says "stereo".

    However, it is entirely possible for that stereo channel to have no sound in it (think of a newsreader, for example). That is, the microphone(s) in the stadium are producing only mono sound that is sent to the TV station. Hence for those broadcasts, you'll get no surround effects.

    I've got a Prologic amplifier, and it has a "simulated surround" mode which can take a mono source and do a fairly good job at creating a more spatial stereo sound out. Maybe yours does, too.

    DJK
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  10. Member dcsos's Avatar
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    Pro Logic II is not like the synthetic "hall," "jazz club," and "stadium" DSP modes found on many A/V receivers. It adds no reverb, no tonal colorations, and no delay-induced echoes. Instead, Pro Logic II naturally extracts all of the ambience and directionality that already exists in the recording.
    http://www.dolby.com/ht/co.br.0107.PLIIListenersGuide.html

    Pro Logic II explained above

    also there's an optional MATRIX MODE that might be in your product for SYNTHESIZING SURROUND otherwise look above
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  11. Just another quick question on this subject. I tried about 4 different recievers before I settled on the one I have now. It seems that every reciever that has Dolby surround, the recievers will only let you adjust the tone controls of treble and bass when running in stereo mode. Whenever in dolby surround or DTS mode, you are not allowed to have control over bass and treble. Any reason why? It was the same on all 4 models. Do higher end units give you treble- bass control or is this just something about dolby. I must say I don't really need to change it as it sounds fine the way it is but I'm just curious.
    Tim
    @Timster: There is a reason for the amplifier disallowing any tonal controls, and it's got to do with the price you mention that you paid for it

    Correct decoding of the Dolby Surround signals relies upon the correct phase relationship between different frequencies present in the audio signal and the differences in phase between channels (L & R).

    A graphic equaliser, which adjusts the magnitude of various frequency bands in the signal, has another side-effect of changing the phase of every frequency band that is not set to 0db gain on the equaliser. Roughly speaking, the more equalisation you put on a frequency band, the more out of phase it will become.

    You generally don't hear this phase change, (I've heard the human ear is insensitive to phase information in audio above 5kHz, but I don't know about the lower frequencies - they're probably detected more as a time-shift rather than phase shift). However the Dolby Prologic decoding process is completely screwed up by the loss of that vital phase information.

    So the amplifier CAN'T apply any graphic equalisation to the incoming stereo signal BEFORE the Prologic decoding process. If your amplifier was more expensive, it could apply the graphic equalisation to the signal AFTER the Prologic decoding - but a separate equalisation circuit is required for each decoded channel (ie up to 5) rather than just two (for the incoming stereo).

    My amplifier manual recommends against using an external graphic equaliser when using Prologic mode, but it is still possible if you can put up with the decoding getting screwed up. However, I CAN use the amplifier's built-in tonal equaliser (bass+treble only) because it applies the equalisation process AFTER the decoding process.

    So, it's lucky you like the sound just as it is

    DJK
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  12. there is always so much missinformation on this subject as I see again from the posts above.

    from an old post of mine.........


    Give Besweat a go, excellent encoder, +freeware.

    With be-sweat you can optimise for Pro-logic I or Pro-logic II

    When using a 5.1 source (AC3 or DTS) you get excellent results with PLII.
    Dont go below 224K when encoding the mp2 file as you will start losing the surround infos.(the seperation between the 5 chanels will not be as good)

    This is from the guy that wrote the program.........

    Quote:
    Dolby Pro Logic (1 or 2 or whatever) is a decoding algorithm.
    unlike in mp3/ogg/aac/etc', when the "brain" is mostly placed in the encoder, and each encoder has his own way of encoding audio samples into the mp3/etc format, and all mp3/etc decoders basicly does the very same thing. in Dolby Pro Logic (DPL), the brain is placed inside the decoder.

    DPL decoder is about interpolating more than two channels out of a 2ch track. (like in a 2.0 --> 5.1 process).
    the DPL/DPL2 implements an adaptive 2x5 matrix :
    [Lt Rt]*MTX=[L R C SL SR LFE]'.
    the left channel output, L, would be equal in this case to : Lt*MTX(1,1)+Rt*MTX(2,1).
    (and so on for R,C,SL,..)

    this matrix is adaptive, and that means that the coefficients changes from time to time, according to the input data.
    the dpl algorithm doesn't "care" if the source is a dolby surround material or a plain stereo track.

    let's think of this very primitive process with a statix dpl-like matrix.
    given a 5.1 source L,R,C,SL,SR,LFE, we would create a 2ch downmixed track with channels Lt&Rt:
    Lt=L+C+(SL+SR)
    Rt=R+C-(SL+SR)
    the (static) decoding process would look like :
    Lr=Lt;
    Rr=Rt;
    Cr=(Lr+Lt)/2; [=L+C+(SL+SR)+R+C-(SL+SR)=L+R+C]
    Sr=(Lr-Lt)/2; [=L+C+(SL+SR)-R-C+(SL+SR)=(L-R)/2+(SL+SR)]

    creating Lt&Rt is principly what Dolby Surround Downmix is about, and creating Lr,Rr,Cr,Sr is principly what Dolby Pro Logic is about.


    as mentioned before, the (adaptive) DPL algorithm can reproduce 4/5/6 channels out of ANY 2ch source, but in case the source was encoded as Dolby Surround, the decoded track would be very close to the original.

    as you can now understand, Dolby Surround "encoding" is a very simple process of simply weighted summings of 5.0/5.1 channels into two channels.

    as for DPL2 & Dolby Surround 2,
    in Dolby Surround (1), we would sum the surround channels into one mono channel, and treat them just like in the example as "(SL+SR)", while in Dolby Surround 2 we would "help" DPL2 seperating them back by giving different weights to each channel. for instance :
    Lt=L+C+SL+0.5*Sr
    Rt=R+C-SR-0.5*Sl

    that's it.
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  13. Dolby Surround encoding is not simply just the weighted summings of the 5.0/5.1 channels into two channels. The centre and surround channels are encoded using a phase difference. Otherwise, there would be no way to retreive the audio back out on the decoding stage.

    Furthermore, the question is whether or not there is a separate matrixing method that is more optimised for Dolby ProLogic II. The last time I looked, there was nothing specific from Dolby itself. As for the author of Besweet, someone quoted from him in another posts revealed that those optimisations were through trial and error and yielded a better output (the Pro Logic II decoder was able to separate the surround left and right channels).

    Now, this gives circumstantial evidence only that perhaps Dolby has another Dolby surround matrixing method that is optimised for Pro Logic II decoders but it doesn't "prove" it.

    Best regards.
    Michael Tam
    w: Morsels of Evidence
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  14. Any one can prove for themselves whether or not you can optimise for Dolby PLII.

    Plug a microphone into your sound card, make six waves, say "front left.....front right.......center....surround left & surround right" encode these seperately with either Bsweet or Headac3e using the appropriate chanelels eg frontleft... frontright etc etc

    Encode your samples once using PLI & once using PLII.

    Mux with any Vid file to make a VCD or SVCD. Burn to CD.

    Play it through you PLII amp.

    I found there is a definite seperation between the surround chanels using a Denon 1802 amp that anyone could hear.

    I also found nothing about this on the Dolby site about 6 months ago.

    quote from my previous post......

    as for DPL2 & Dolby Surround 2,
    in Dolby Surround (1), we would sum the surround channels into one mono channel, and treat them just like in the example as "(SL+SR)", while in Dolby Surround 2 we would "help" DPL2 seperating them back by giving different weights to each channel. for instance :
    Lt=L+C+SL+0.5*Sr
    Rt=R+C-SR-0.5*Sl
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  15. . For instance watching sports events on TNT and TBS the surround is great and you really feel like your at the game, but when watching ESPN it seems like it's not in surround.
    I used to work at ESPN (I'm one of the lucky ones that escaped ).

    ESPN, in all honesty, will broadcast in standard stereo, or just use mono and send them to both audio channels. Only during a major event do they go to stereo. I used to sometimes work in master control for the network (the guy sending the signal to transmission to go up to the satellite), and I would have to do a diving move to hit the switch to go from mono to stereo when something big like the NFL was being aired.

    The network will supposively be digital at the end of March, so you can expect a little better quality when that happens.

    I haven't worked at the network since the end of 2000, but I believe the audio situation is the same as when I left there. Maybe their still using 1" tapes, too.
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  16. Originally Posted by Oracle
    Any one can prove for themselves whether or not you can optimise for Dolby PLII.
    Yes you are right. What I meant to say rather (but on review of my previous post I put down poorly) is whether if that's the way that Dolby does it... It may well not be. If it is not, is there a detrimental effect if the audio is played back on standard ProLogic I receivers?

    Regards.
    Michael Tam
    w: Morsels of Evidence
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  17. @apollo 1980:

    Your experience with ESPN seems to match precisely with my orignal message - Timster is probably listening to a mono source being broadcast in "stereo" but without any differences between L & R so there is nothing for his Prologic amplifier to decode.

    I notice also here in Australia that major AFL matches (Grand Finals etc.) sound better through the Prologic setting on my amplifier. Regular weekly matches have historically sounded better through the "simulated surround" setting, although that is changing...

    DJK
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  18. Member Cornucopia's Avatar
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    Oracle, to clarify--

    1. On decode, Cr=[Lt+Rt]/2=[(L+C+{SL+SR})+(R+C-{SL+SR})]/2=
    [L+C+R+C]/2=C+L/2+R/2
    This show C as being the strongest, which is why it can be isolated further in ProLogic modes.

    2. Officially as per Dolby, AC3 5.1 will not and should not use the .1LFE channel during downmix. So all of the previous mentions should be 5.0, not 5.1.

    3. Even if you give a Dolby Surround encoder 5.0 channels, it really-by your own example-just sums the 2 rear/surround channels, so every source is in essence a 4 channel (LCRS) source.

    4. You're guessing (and I might venture that the author of BeSweet is also guessing-no flames please) about the action of the PL2 decoder. If you're gonna do matrix math, you have to take it to it's logical conclusion. You didn't in your example. I won't here, cuz it'll be too long and I'm already longwinded enough. Hint: should read..."SR=***+^^^blahblahblah..."

    5. Past readings of the decoding action in PL1 has revealed that the same original decode matrix is in effect, but that the "steering" is downstream of the decode, using comparators and varying the gain of the dominant and non-dominant channels (much like the old quad SQ/QS stuff). While PL2 includes other things, it probably still builds upon this same foundation.

    6. BeSweet and HeadAc3e should say they use "Dolby comparable" or "Dolby Surround-like" or "PL1-esque" encoders, since they certainly aren't certified by Dolby (else they would be $$$ with licensing) and while this may not make a huge difference, it's technically not the same as the Dolby algorithm. Please don't flame, I'm really impressed with these apps and will recommend them to people, but I've gotta be honest.

    @appollo1980:
    that's what I thought was going on.

    Scott
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  19. @corn


    1. On decode, Cr=[Lt+Rt]/2=[(L+C+{SL+SR})+(R+C-{SL+SR})]/2=
    [L+C+R+C]/2=C+L/2+R/2
    This show C as being the strongest, which is why it can be isolated further in ProLogic modes.

    2. Officially as per Dolby, AC3 5.1 will not and should not use the .1LFE channel during downmix. So all of the previous mentions should be 5.0, not 5.1.

    3. Even if you give a Dolby Surround encoder 5.0 channels, it really-by your own example-just sums the 2 rear/surround channels, so every source is in essence a 4 channel (LCRS) source.

    4. You're guessing (and I might venture that the author of BeSweet is also guessing-no flames please) about the action of the PL2 decoder. If you're gonna do matrix math, you have to take it to it's logical conclusion. You didn't in your example. I won't here, cuz it'll be too long and I'm already longwinded enough. Hint: should read..."SR=***+^^^blahblahblah..."

    5. Past readings of the decoding action in PL1 has revealed that the same original decode matrix is in effect, but that the "steering" is downstream of the decode, using comparators and varying the gain of the dominant and non-dominant channels (much like the old quad SQ/QS stuff). While PL2 includes other things, it probably still builds upon this same foundation.

    6. BeSweet and HeadAc3e should say they use "Dolby comparable" or "Dolby Surround-like" or "PL1-esque" encoders, since they certainly aren't certified by Dolby (else they would be $$$ with licensing) and while this may not make a huge difference, it's technically not the same as the Dolby algorithm. Please don't flame, I'm really impressed with these apps and will recommend them to people, but I've gotta be honest.
    1-Dont know what youre getting at?
    2-If you mean you cant downmix the LFE of a 5.1 chan source to Prologic ,of course you can(distribute evenly to left & right chanels)
    3-Remember a big featute of PLII(dolby.com), more bandwidth&seperation on the surround chans.(3/2)
    4-Please explain
    5-What apps are dolby certified, maybe I could try a demo & compare.

    Did you find any infos on Dolby.com about if a certified encoder encodes a source any different for PLI & PLII-would be great if someone has infos on this & would prove the authors of Besweet & Headach3e are guessing.
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  20. Member Cornucopia's Avatar
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    @Oracle:

    #1. You had Cr=C + L + R, I had Cr=C + L/2 + R/2. This is much better separation than what you're suggesting will happen.

    #2. I don't mean that you CAN'T manually downmix, or script for automatically batch-downmix. I say that according to Dolby, using a DD correct decoder, you shouldn't be and won't be allowed to automatcally incorporate the .1 info when downmixing. They explain the reason why on their site.

    #3. Yes, but it's still just a 4.0(LCRS) source encoding matrix. I just confirmed this on their website.

    #4. Dolby hasn't revealed enough on their website as to how they are achieveing 5ch output with the PL2 decoding matrix--specifically how they get SL and SR separated, so I'm not going to venture to guess at it just yet. I'm just saying you shouldn't either, unless you have definitive info and explain it all thoroughly.

    #5. Try Dolby's list of Licensed Encoder manufacturers.

    Scott
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