‘Mark 66′ asked recently on the Digidesign User Conference….

I am looking to make an LtRt from a 5.1, is there a plugin that will do this?

‘TimNielsen’ replied with….

This will encode, but I’m not sure it will go directly from a 5.1, normally you feed the LtRt input L, C, R, and a mono Surround channel to make the LtRt.  It would be fairly easy to take your 5.1 tracks and bus them appropriately to the input.
If you just want to make a stereo from the 5.1, and not a true LtRt, then you normally bus your 5.1 tracks to a stereo bus, and then drop the center channel -3dB, drop the surrounds -6 and pan the Ls to L, and the Rs to R, and either drop the Subwoofer -10 or lose it altogether. I usually then run all those through an aux track, and take the oveall level of the stereo down a couple of dB before recording too, since adding in the center and surrounds to the L and R, even dropped as they are, can and will probably still overload the channels at times.
But for doing a true LtRt, the Dolby Surround Tools is the only thing I know of, since it’s a Dolby matrix that needs to be created, not sure anything else can make you one.

‘strangeLoop’ added…..

Here is the one from Neyrinck Audio.

‘JFreak’ agreed…

Neyrinck is the one to choose, even though Dolby is Dolby, it is not that good.

‘bad jitter’ added….

Hmm… I have Dolby and the GUI is PITA, agreed. But are you saying that Neyrinck sounds better?

‘Frank Kruse’ pointed out…

The neyrink doesn´t have a decoder so you won´t be able to hear what you’re doing.

‘JFreak’ suggested….

Maybe it’s just me, but I get better end results using Neyricnk’s. That said, I don’t own either, I just trash an extra iLok key when I need those plugs
IMO encoder is enough, I always use a hardware decoder (home theater consumer stuff) to listen to the mix as that is what the customer is also using.

‘dr sound’ commented about Neyrinck’s lack of a decoder….

I talked with Paul Neyrink at NAB and he told me he is very close to releasing the decoder with the PLII . I will purchase one as soon as that happens.

‘laki’ suggested a different route…

SRS Labs make a plug too. It’s decent but I prefer the Neyrinck. Not that it sounds better, but it is adjustable. My only gripe with the Neyrinck is that every instance eats up a whole DSP chip!
If you’re doing an involved 5.1 mix and need to do multiple fold-downs for stems etc, you may run out of DSP. The SRS plug is less DSP hungry.

But ‘Stylin’ Audio’ pointed out….

SRS left us owners for dead – they are not supporting/developing their plug anymore.

‘Postman’ said…

Please, let’s not confuse the terms LtRt and LoRo. In PT you can route the surround mix to LoRo, a.k.a. good old stereo. Yes, Dolby decoder will play it just like any other stereo recording can be played, but what emerges from the surround speakers is not the same as when the surround mix is encoded into an LtRt by an actual encoder. LtRt and LoRo/stereo are not the same thing.

‘TimNielsen’ apologised…

Yes, sorry if I confused anyone, the method I listed will NOT make an LtRt, which is a Dolby Specific ‘encoded’ system of merging L, C, R and a Mono Surround channel into a stereo stream. I was simply listing a fold-down method to make an LoRo, as was noted, which is simply a normal stereo stream that won’t lose information, like would happen if you just took the L and R of a 5.1, obviously you’d lose your center and anything in the surrounds. So what I was listing was a crash-down, just in case the person posting wasn’t talking about a true LtRt. Sometimes I hear people refer to a stereo mix as an LtRt, when in fact they’re simple talking about a crashdown, which as was noted. So I didn’t mean to imply I was listing a formula to make an LtRt without a plugin or hardware encoder, it can’t be done. You have to use either the Dolby or the other one (which I didn’t even know existed).

‘Postman’ replied…

Hi Yes, that was my main point. Thank you for clarifying. I’m seeing regular intermingling of the terms because some people (not you, but some others) do not know any better. It is a regular mistake in the Post forum too.

‘gsilbers’ commented…

we do the “crashdown” (foldown) to make LTRT and we go through a dolby E encoder to layback 5.1+LTRT. it passes QC fine but maybe its different than ltrt for a dvd. Although we send tons of foldown ltrt to dvd houses/blueray and never have had any problems.so maybe they do something else to it. so now im a bit curious on the plugin route and why would it be different.  btw we do this we many many movies and tv shows for fox , univ, disney etc.

TimNielsen came back…

Please be clear on the terminology here. If you say you are using ‘crashdown’ method to make your LtRt, then you are NOT making an LtRt, you are making an LoRo! There is a HUGE difference. All you are doing is making a stereo version of your mix. It has no information for the center channel, or surround channel. Now the dolby DECODER might still stear some information to those channels when you play it back, but what you have made is mostly certainly not an LtRt. The term LtRt (Left Total, Right Total) only applies to a 4 channel stream (L, C, R, S) that has been specifically encoded through the Dolby Matrixing scheme, to embed the C and S information into the L and R channels, so that a decoder can properly find them, extract them, and steer them to the C and S channels.
Hence it is, and must be a two part process. You must specifically encode, and decode an LtRt. You absolutely cannot make a true LtRt any other way. What you are making is fine, we make them all the times as well, a simple stereo version, for instance for the editors to drop into their Avid. But it is NOT an LtRt, which is a very specific thing for a film print or DVD. The nice thing about an LtRt is that it can play just fine as stereo, it doesn’t need to be decoded, if you don’t decode, you just hear stereo. So this is used on the stereo track on a DVD. Then if a person at home has a Dolby Surround decoder in their receiver, it will extract the channels and give surround. Of course nowadays, I can’t imagine there are many left using Dolby Surround decoders, everything is Dolby Digital and now moving towards Dolby True HD, but anyway…  So really, what you are doing, you should call it an LoRo (Left Only, Right Only), and not an LtRt. Hope that clears up any confusion. If you’re not encoding it via a hardware of plugin, you are not making an LtRt.

‘CCash’ agreed…

Right. That is not an LtRt, even if you label it that way. You are getting away with it because it is usually very difficult to determine if someone has given you stereo or an encoded LtRt, even when decoding it to LCRS. That’s because the decoders do a pretty good job of steering things to the correct speakers… but you will be at the mercy of the decoder’s speaker steering, and it will not retain any of the rear-front panning decisions you made in the 5.1.

‘MixMonster’ chipped in…

I use SurCode by Minnetonka Audio. It’s both encoder and decoder, easy to use and I’ve never had any problems with it.

‘The Missile Silo’ added….

Having worked in DVD/Audio Restoration for a number of years we used Neyrinck (specifically the Sound.Code for Dolby Digital version for our AC3′s.). I did a shootout once between or Dolby plug-in encoder and the Neyrinck, hands down Neyrinck was the obvious choice.

‘TimNielsen’ mussed…

Curious, obviously the decoding matrix will usually steer dialog to the center correctly, since it’s perfectly in phase on the L and R. But will a decoder street ‘anything’ the surround channel from an LoRo? Never tried, but that’s the part I assume would just go missing, and instead you’d get a usable LCR out of it. Which, as you said, is what makes it hard to know from listening to a file if you have a real LtRt or not.

‘Postman’ replied…

Absolutely! The less phase coherent is left-right, the more it will be drawn to the surround channel(s). With Pro Logic 1 and 2, stereo reverb gravitates toward surround always. With Pro Logic 2, there are different modes that alter its behaviors, but it tends to “bend” hard left and hard right toward the surrounds. Some music modes make the effect really great, but at the same time do not give the center channel a firm anchor, which can really screw with dialog. I’ve taken a liberty to turn your remark into a question. Sound that is out of phase between left and right will head into the surrounds, so if you hear some things like ambiences and specific panning stuff like fly overs or pass-bys sounding very out of phase ,between left and right, you are likely hearing an LtRt. But, as you point out, there is no simple way to tell for certain. Anyone can make out of phase information. The trick with true LtRt is there is a 90 degree “all pass” type of phase shift on all the surround material. THAT is not as easy to do as simple routing and 180 degree phase shift. But that is what allows a mixer to pan a mono sound partially front to back without it being pulled toward left or right. Sorry, I’m talking geek speek.

‘TimNielsen’ came back…

No, it’s good. I’m learning stuff. LtRt’s have always been a bit of a mystery to me. We always make them, but the mixers monitor it coming back from the magic device, and make adjustments based on what they hear, mostly capping volume and maybe riding the dialog a bit! So it’s good to get a better understanding of what is happening. It’s another one of those technologies that was genius in it’s day, but I wish we didn’t have now, like Dolby Digital. The most exciting thing for me about Digital Cinema, is 16 available tracks of 24, 48k uncompressed audio!

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