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Downmix 5.1 to 2.0 - without a specific plugin (but with a modular environment)
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13th June 2012
Old 13th June 2012
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Downmix 5.1 to 2.0 - without a specific plugin (but with a modular environment)

Fellow engineers,


I know this is a topic that is popping up on a regular basis. But the answers I got out of the threads were either confusing, or directing to specific downmixing plugins.


Let's assume I have a 5.1 mix that I want to downmix to 2.0 Lt/Rt so that I do not need to do a specific discrete 2.0 mix.

I digged around in this board section a bit, and got several answers. I do know that there are certain tools exising, and tons of different routes to go. But let's keep it simple please.


One way I found was to simply use a 5.1 bus, and then forward the individual channels from the 5.1 bus (via send) to a 2.0 bus with settings like:

Quote:
C -6dB goes to both L and R
L -3dB goes to L
R -3dB goes to R
Ls -6dB goes to L
Rs -6dB goes to R
Or even:
Quote:
The RPGA Document (P&E Wing) recommends -6 on L/R, Ls/Rs & -9 on centre, with LFE from -9 to taste.
Quotes can be found (for example) here:
Is there a general specs for downmix for dekstop and software player
Is there a general specs for downmix for dekstop and software player


Wikipedia however mentions this:
Quote:
Lt = L + -3dB*C + -3dB*(-Ls -Rs)
Rt = R + -3dB*C + -3dB*(Ls + Rs)

(where Ls and Rs are phase shifted 90°)

Sadly enough, I can't find the ITU Downmixing plugin, only the PDF hinting at it and no further info regarding settings they use as listed above. I'm not on PT, so I can't get Mix51, and Minnetonka is way out of my pricerange.


So I thought:
"Why not use a modular environment like DDMF's MetaPlugin and create your own chain". The thing is: how.

I mean, routing 6 channels to gain plugins and then to the 2.0 output of the plugin is simple. But I'm wondering on the 90degree shift of the Surround Channels, what's up with the -Ls -Rs and how to pull that off.

Is it really that simple with the first two mentioned methods?
Or do I need to(!) add phase shifting in order to get a DPL II comilant mix?
If so, how do I do that actually?


Thanks in advance for answering.
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13th June 2012
Old 13th June 2012
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The phase shift is if you're making an "Lt Rt", not a 2.0 LoRo mixdown. If you want something that will decode through Dolby Pro Logic with the surround coming out the back speakers, do this and it'll be approximately like how it would sound through the encoder.
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13th June 2012
Old 13th June 2012
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Yes, I am talking about Lt/Rt as in DPL II compilant.


The thing is, do i simply "shift" the Ls channel to -90degree and route it L, and then shift the Rs channel to +90degree and route it to R?

I kind don't understand yet the thing with -Ls/-Rs and Ls+Rs.

Also... are the other mentioned methods not DPL II / Lt/Rt compilant? Because there don't seem to be a phase shift happening, just gain adjustments.
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13th June 2012
Old 13th June 2012
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Quote:
Originally Posted by Mister Fox View Post
Yes, I am talking about Lt/Rt as in DPL II compilant.


The thing is, do i simply "shift" the Ls channel to -90degree and route it L, and then shift the Rs channel to +90degree and route it to R?
Both are put in quadrature, with an all-pass filter, I just don't know how you'd do that with modular gear

The poor-man solution is to sum the Ls and Rs, mult this mono signal to the Lt and Rt at -3, and flip one side 180 degrees out of phase. This sort-of works unless you have straight front-back panning.

Last edited by iluvcapra; 13th June 2012 at 05:08 AM.. Reason: fix tag
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13th June 2012
Old 13th June 2012
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Hm... don't think "modular", but normal channelstrip routing. Would that still apply?

I try to understand what's going on here and how to pull this off "the hard way" (meaning the "old" way, before plugins and hardware modules helped in that process). Especially the 180 degree rotation.


Furhermore, how would someone setup an environent if you're using 6.1 (which adds an additional center surround speaker) or even up to 9.1?
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15th June 2012
Old 15th June 2012
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Noone can help?
Or did you all really access specific plugins/hardware modules only?
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15th June 2012
Old 15th June 2012
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15th June 2012
Old 15th June 2012
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Quote:
Originally Posted by Mister Fox View Post
Fellow engineers,


I know this is a topic that is popping up on a regular basis. But the answers I got out of the threads were either confusing, or directing to specific downmixing plugins.


Let's assume I have a 5.1 mix that I want to downmix to 2.0 Lt/Rt so that I do not need to do a specific discrete 2.0 mix.

I digged around in this board section a bit, and got several answers. I do know that there are certain tools exising, and tons of different routes to go. But let's keep it simple please.
If you want to keep it simple use one of the dolby-compliant plugins.

All else is way more complicated.
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15th June 2012
Old 15th June 2012
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Wait, you want to keep it simple, then ask about 6.1 and 9.1?
You need to study some DSP before you even understand what's happening in the encoding. Even if you could encode, you also need to decode it in your monitoring chain - otherwise you don't know what you're doing. And you can certainly NOT roll your own decoder, because they are really complex.
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16th June 2012
Old 16th June 2012
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Quote:
Originally Posted by Mister Fox View Post
Noone can help?
Or did you all really access specific plugins/hardware modules only?
We usually just call Coach and he comes over with the DMU

I would hasten to add that if you don't want to buy these plugins, you can always rent the Dolby Surround Tools from Digi... er, Avid for like $30 for the day.
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16th June 2012
Old 16th June 2012
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Then let's stick to 5.1 only. I was just curious if the same rules apply for 6.1 and higher streams, but 5.1 is fine for the time being.

I do know about the DPL II plugin by Minnetonka, but I don't have the funds yet to get it, or even rent it (didn't find 30bucks/day renting, only per week).


What I try to understand is the Ls/Rs channels and how to mix them together (if they need to be mixed), how to rotate them, etc. The Wikipedia entry is a bit confusing with the -Ls-Rs and Ls+Rs. Also, is the rotation to 90 degree to both sides (+ and - 90) or just one side (- 90)?

Don't get me wrong here - setups like this must have existed before suitable plugins and hardware modules existed. I'm curious what's behind it.


Of course I need a Decoder for realtime checks. But everything around it is what's interesting me.

Thanks again.
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16th June 2012
Old 16th June 2012
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Quote:
Originally Posted by Mister Fox View Post
Don't get me wrong here - setups like this must have existed before suitable plugins and hardware modules existed. I'm curious what's behind it.
You mean there was dolby before dolby? Dolby Stereo didn't exist before it was invented and neither did dolby encoders/decoders.

Before plugins there was and still is the analog dolby encoding/decoding boxes of various flavors.
Before dolby made those there wasn't any dolby format. This was in the late 60ies of the last century.

The principles are based on MS-Stereo principles (sum and difference matrix). The "secret" behind dolby is the directional dominance circuit (in the decoder) that prefers the channel with the greatest audio energy and ducks all other channels accordingly to increase channel separation. Without this the channel separation in this matrix technology would only be 3dB AFAIK.

There was no wheel before people invented it.

Not sure what you're asking? You want to emulate the dolby system without an analog box or a DAW using "modules" that were used before dolby-stereo was invented?
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16th June 2012
Old 16th June 2012
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Quote:
Originally Posted by Mister Fox View Post
What I try to understand is the Ls/Rs channels and how to mix them together (if they need to be mixed), how to rotate them, etc. The Wikipedia entry is a bit confusing with the -Ls-Rs and Ls+Rs. Also, is the rotation to 90 degree to both sides (+ and - 90) or just one side (- 90)?
I'm no DSP expert, but '90 degree rotation' is not a simple process. It's not like shifting a single frequency by 90 degrees, but shifting the whole signal that consists of a number of arbitrary frequencies and noises. It involves an 'all-pass filter', which you can't achieve just by routing things around..... Besides simply flipping the phase of the surround signal in one of the channels - give it up

Quote:
Originally Posted by Mister Fox View Post
Don't get me wrong here - setups like this must have existed before suitable plugins and hardware modules existed. I'm curious what's behind it
There was always some hardware.
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16th June 2012
Old 16th June 2012
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Quote:
Originally Posted by apple-q View Post
Not sure what you're asking? You want to emulate the dolby system without an analog box or a DAW using "modules" that were used before dolby-stereo was invented?
Not quite.
I'm indeed aiming on the current boom in terms of surround mixing tools and the need to also provide a compatible 2.0 mix. I digget around on the net a bit, asked a couple of plugin providers in that section and it was always like "just to a Lt/Rt mix, the values are known - a hardware DPL Decoder does a realtime check".


I only wanted to know what's behind it and why some say "just mix it", other sources say "there is a phase shift involved" and even more sources say "use a dedicated plugin".


I think danijel is right, I should simply forget it. But the time M/S came up, it was also some mystery - now it's common knowledge. Guess I'll simply trust the surround tool developers to provide proper downmix parameters. Because I can't find that (indeed interesting) IRT downmix plugin, only the PDF hinting at it. And... I don't use PT, else I'd get Mix 51.


Thanks anyway for the help.
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16th June 2012
Old 16th June 2012
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Get an old dolby seu4 harware encoder. I got mine for ,$30.

Sent from my DROIDX using Gearslutz App
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17th June 2012
Old 17th June 2012
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Thanks for the mention, but this module is downmixing 4 channels into 2 and not 6 (5.1) into 2.


I guess I stick to what I said earlier:
Trust the software providers to offer suitabe downmix parameters.
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17th June 2012
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Quote:
Originally Posted by Mister Fox View Post
Thanks for the mention, but this module is downmixing 4 channels into 2 and not 6 (5.1) into 2.


I guess I stick to what I said earlier:
Trust the software providers to offer suitabe downmix parameters.
LtRt unfolds to LCRS (in it's simple form) which is why a analog dolby encoder has 4 inputs and 2 outputs.

To put it simple:

a LtRt to 4.0 matrix works like this:

L=L
R=R
C=L+R
S=L-R

plus the patented dolby-only directional dominance circuit (not sure how it's called officially) which you can not "emulate" with just a generic "module" of your mixer.

Downmixing and dolby matrix-encoding have nothing to do with each other.
Matrix-encoding doesn't mean down-mixing the way those terms are used in practice.

You can down-mix 5.1 to regular non-dolby 2.0 simply by using a mixer (could be one from 1940 as long as it has 6 channels and a stereo bus, if you prefer a "module" from before dolby was invented)
If you want to matrix encode it you want to down-mix 5.1 to 4.0 (LCRS) and send that to the matrix encoder which will deliver a matrix-encoded 2.0 version also called LtRt.
The advantage of the plugin is that you can go straight to LtRt from 5.1 without doing the down-mix manually first and then matrix-encode.
For actually dolby-stereo optical printing you will further need to apply dolby-A or dolby SR noise reduction to make it compatible.
To officially label it a dolby film you need to use a dolby approved theatre and mastering and pay a license fee. But this is for film optical only.

As mentioned before: Get an SEU4 on ebay and you have just about the cheapest dolby encoder you can buy.
But again: A dolby-matrix doesn't do a down-mix it "encodes" LCRS to LtRt.

Maybe you are asking about straight down-mixing 5.1 or 7.1 to stereo?
If yes you can simply use your mixer or use the PT10 built-in down mixer plugin that has plenty or presets depending on your speaker-setup and taste.
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17th June 2012
Old 17th June 2012
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As said earlier, I'm not on PT (last PT I have is 7.4), I'm mainly using Cubase and Wavelab as my main workstations. Cubendo has a 6to2 plugin but I've never trusted it to be honest and couldn't test either, since I don't have a 5.1 setup yet.

Then again, I'm curious to dive into the 5.1 (audio only) in the near future and wanted to ask if there are ways to make 2.0 ProLogic II(!) compilant mixes through normal means, or something like Mix51 from Neyrinck did - but in VST form.

Looks like my (only?) way to go is with Minnetonka, a hardware module that goes from 5.1 straight to 2.0 DPL II, or hope that the 5.1 tool I plan to use in the near future (either AnyMix or SpatialAudioDesigner) has a compatible downmix preset.

Of course I can't expect wonders to decode that stream again with a suitable decoder box - for this I will go the DPL II route through Minnetonka eventually.



Hope this clears the confusion. Again, thanks for contributing.
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17th June 2012
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Quote:
Originally Posted by Mister Fox View Post
Then again, I'm curious to dive into the 5.1 (audio only) in the near future and wanted to ask if there are ways to make 2.0 ProLogic II(!) compilant mixes through normal means.
I assume "normal means" translates to "for free, without buying anything etc.".
The answer to that is no.
You will need a Dolby Prologic II encoder. And if you want to hear what you're doing you will need to monitor through a decoder as well because certain sounds can have quite unpredictable results after going through encode/decode-chain.
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17th June 2012
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I'll agree with the last post, but you can get 80% of the way there without a Dolby compliant LtRt encoder if you realize certain aspects of PLII decoding. The 90degree networks are only important if you pan between surround and front channels. Mid pan there would be a null without the phase shift. But anything hard panned to Ls and Rs works fine without it. Keep in mind the surround channel in ProLogic is mono, any differences in post-decode Ls and Rs are synthesized after the decoder. Also, in the original "Dolby Stereo" spec (that's what this matrix system was in theaters before ProLogic) includes modified Dolby B type noise reduction for surround only, and surround bandwidth limited to 7KHz. The bandwidth limit was to reduce HF crosstalk caused by optical slit misalignment in film projectors, so that can be ignored, but low level surround material may end up sounding a little dull because of the NR, so be ready to use a shelf EQ to boost above 1KHz during low level surround only. 6db max should do it.

Monitoring the results of 5.1 to LtRt through a PLII decoder is critical because the steering logic can reposition elements of your mix unexpectedly. PLII uses several methods to hype adjacent channel separation, as the raw post-matrix-decoded separation between adjacent channels is only 3dB. One method involves dynamic steering tha,t while a standardized method, can steer things in unexpected ways. Mastering for LtRt ways involved listening to a standard decoder so that steering errors (Todd-isms) could be pre-compensated for. Decoders also delay the surround channel by 15-20ms as a separation enhancing method, keeping the image forward should the same sound appear post-matrix in front and surround channels.

Even if you use a plugin, it should not be considered a passive set/forget process. The matrix is going to mess with your mix, it's what it does, and why we have 5.1 now.

By the way, 6.1, 7.1, 9.1, and 11.2 are all synthetic processes done on 5.1 raw material. There are a few 7.1 discrete tracks, more now than ever, but the theatrical and broadcast standard remains 5.1. Since there are several non-standard processes involved, it's probably not worth trying to pre-comp for any of them.
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18th June 2012
Old 18th June 2012
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Hm... interesting read. Thanks for that.


So my only way is to:
1) get a DPL II plugin to do the trick (while cross-checking with a decoder)
2) only stick to 5.1 and ignore 2.0 streams, since the player takes care of that (which locks out possible 2.0 interests)
3) don't be a lazy tool, do twice the work and create a discrete 5.1 and 2.0 stream


I feared as much - only wanted confirmation and maybe ask for other means (indeed: either free or affordable). Thanks for contributing. This pretty much answers all my questions.
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18th June 2012
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Quote:
Originally Posted by Mister Fox View Post
Hm... interesting read. Thanks for that.


So my only way is to:
1) get a DPL II plugin to do the trick (while cross-checking with a decoder)
2) only stick to 5.1 and ignore 2.0 streams, since the player takes care of that (which locks out possible 2.0 interests)
3) don't be a lazy tool, do twice the work and create a discrete 5.1 and 2.0 stream


I feared as much - only wanted confirmation and maybe ask for other means (indeed: either free or affordable). Thanks for contributing. This pretty much answers all my questions.
4) Buy a used SEU4 on ebay for cheap.
#23
18th September 2012
Old 18th September 2012
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Stereo Downmix Monitoring

I'll offer one more interesting option for this type of situation as this is what our solution was built for and will save heaps of time in the mixing process.

Check it out at www.nufeeld.com

The Embracing Sound technology used for our Corego system can be thought of as a m/s (mid/side) reproduction system. Of course I can talk all I want about it and I'm only too well aware of that you need to experience it first hand to realise the extraordinary depth and positioning information made possible by this.
The beautiful thing is it uses no Phase Magic, which many other similar concepts will, and which generally makes them unsuitable as a reference tool in a studio environment. This very clean and relatively simple technology reproduces/offers the cleanest time domain possible....again it needs to be experienced.

With the Corego you get a complete "Stereo Downmix Monitoring System" which in essence becomes a huge time saver for people working in 5.1 surround as you're actually monitoring the stereo downmix of a 5.1 input while retaining the surround experience. It means no need for a separate mix session doing the stereo mix and no late surprises (ie. unnoticed phase cancellations in the surround channels) when listening to the stereo downmix from the DVD/Blu-ray. As a bonus the Corego rack also works as a stereo downmix algorithm offering your 5.1 to stereo downmix on +4 dB balanced XLR outputs.

It might not be exactly what you were asking for but still

If it sounds interesting and you'll be visiting Sweden...contact me and I'll set up a demo.
#24
18th September 2012
Old 18th September 2012
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I for one would use IOSONO Anymix. It does quite a good job, although the many options are sometimes kinda confusing. But I've never had a smoother up/downmix plug-in.
#25
28th September 2012
Old 28th September 2012
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for downmix by far the easiest thing to do is insert a Spanner.
or better yet, render with the audiosuite spanner for faster than realtime folddowns.
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