2.0 Downmixing and the CP750 / DCP2K4

[Ryan Gallagher]

Some contingency thinking out loud. Word seemed to spread fast, but our State Theatre venue experienced another relatively catastrophic flooding event with a water main break that found several entry points past the concrete basement walls. This was the same water main that got us in a similar fashion about a year ago. Timing is about as bad as it gets... the Paramount is closed for renovation with chairs, carpet, bars, and all production/cinema equipment already removed.

Fortunately or unfortuanately, this occurred with a full house right before a film (which cancelled). I call it fortunate, better than it happening overnight with no staff on site to initiate the response.

Our current status is remediation and drying... stage deck was pulled to allow airflow and drying to the support 2x4 grid below. Cancelled about a week of shows so far. We have fairly aggressive re-opening plans, but some cinema contingencies might justified to plan for:

If our stage deck is not at least half way restored, or has wet paint by our first film, I will not be able to roll out the center and LFE channel equipment for our normal 5.1 setup.

Is there a way to do a 5.1 to 2.0 downmix (or LR+Lsur+Rsur) using our existing equipment? Our L+R feed the suspended Live PA through an audio desk.

My initial thoughts:

2.0 film = No change, everything ready to go.

Mono film = Easy, just re-route C within the Doremi DCP2K4 to both L and R, and adjust desk fader to ear.

5.1 film = Harder... was thinking maybe we could take the H/I unbalanced output on the 750 to the live desk for a 2.0 presentation? This output should be active regardless if DCP has dedicated HI/VI content.

My skimming of the 750 manual again did not reveal a native downmix feature for the AES digital inputs.

If we have this solution in pocket the only thing preventing slightly audio compromised screenings is getting the auditorium reconditioned. The stage deck could be a work in progress still as our screen is a roll down. Bottom masking can be ignored if we are not placing C+LFE.

[Marcel Birgelen]

I guess you have a halfway decent mixing deck with routable chanels and 6 balanced inputs? Make a custom DB25 cable that feeds those channels into your PA mixing deck and take it from there? Center and possibly LFE should be mapped to both L and R, but since most mixing decks know how to handle microphones, that shouldn't be a feature problem either.

[Ryan Gallagher]

I guess you have a halfway decent mixing deck with routable chanels and 6 balanced inputs? Make a custom DB25 cable that feeds those channels into your PA mixing deck and take it from there? Center and possibly LFE should be mapped to both L and R, but since most mixing decks know how to handle microphones, that shouldn't be a feature problem either.

Our console is a Midas M32. It can do AES50 directly but not AES pairs, and yeah... such a breakout to XLR might already be in use for the existing configuration, I haven't looked at the physical routing closely in that room. Might just be a physical repatch to 6 inputs on the console and applying our own downmix?

At home I have a doremi branded Male XLR to male DB25 analog input breakin. Is the pinout gonna be the same on that or was that Doremi pinout before merger with dolby? If it's the same it would work with a DB25 gender changer, which I also have. I have a similar Dolby labeled one but it is female on the XLR side, so more adapters required even if the pinout is correct.

[Ryan Gallagher]

A quick refresh reminds me Doremi and Dolby pinouts are incompatible. (Tascam vs Sony pinout). If venue is not already using a 6 channel output breakout, perhaps the Dolby cable I have with gender change and 6 turnarounds is the most direct aside from building a new one.

Also correction, I realize now the H/I output thought is severely compromised down to MONO. For 5.1 films anyway, our own downmix via the desk does seem the most bang for the buck.

[Marcel Birgelen]

Yeah, you might need to make SOME concessions if all the input chanels on your mixing console are taken. And yes, use the Analog output from your CP750, getting the AES to work on any mixing console will be a nightmare. Maybe if you have a fancy IMS3000 you may try to use AES67 if you're into a day of debugging and frustration.

I've done downmixig on PA consoles for movies many times. I think it's the most reasonable way to do it, as you have the maximum amount of control of the downmix, especially when mixing in the center channel, as you might want to give that some emphasis or even some compression to keep the dialog usable... all depending on the type of sound system you're using. A PA system isn't optimal for cinema, but it beats a silent movie... at least if done right.

With regards to the DB25 to XLR cable: I'm not sure what type the Doremi cable is. Most DB25 to XLR cables use the TASCAM standard, but Dobly has their own layout:

image.png

Edit: Added some information regarding AES and you apparently already concluded yourself that the Doremi cable uses the TASCAM standard.

[Ryan Gallagher]

Yeah, you might need to make SOME concessions if all the input chanels on your mixing console are taken. And yes, use the Analog output from your CP750, getting the AES to work on any mixing console will be a nightmare. Maybe if you have a fancy IMS3000 you may try to use AES67 if you're into a day of debugging and frustration.

I've done downmixig on PA consoles for movies many times. I think it's the most reasonable way to do it, as you have the maximum amount of control of the downmix, especially when mixing in the center channel, as you might want to give that some emphasis or even some compression to keep the dialog usable... all depending on the type of sound system you're using. A PA system isn't optimal for cinema, but it beats a silent movie... at least if done right.

With regards to the DB25 to XLR cable: I'm not sure what type the Doremi cable is. Most DB25 to XLR cables use the TASCAM standard, but Dobly has their own layout:

image.png

Cheers, plenty of channels available. We have a "film" preset we load that is wide open other the L+R film channels, an intro mic and stereo laptop for walkin music. If it's already using such a breakout we could leave the Lsur and Rsur active and not routed to the desk, or take them through the desk if we feel we will need to for downmixing reasons.

I'll take a look at how we are already handling that analog output connection on Monday, mid stage rebuild.

[Harold Hallikainen]

On DB25 pinouts, as I recall, USL and most others used a pinout from THX. Then AES adopted AES59-2012, which used a pinout developed by Tascam. I think USL made the transition from the THX pinout to the AES59 pinout when moving from the JSD-100 to the JSD-60. Or it may have been between the JSD-80 and the JSD-100. I remember a big discussion as to whether to stay with THX or move to AES59.

[Marcel Birgelen]

"The nice thing about standards is that you have so many to choose from; furthermore, if you do not like any of them, you can just wait for next year's model."

Was the THX pinout actually balanced? I know there are a few home theater amps that use something called a THX DB25 layout, but none of them seem to be balanced. I've got a beefy 5 channel amp lying around from ROTEL which used to be part of my home cinema setup like 15 years or so ago, which is also THX-whatever-certified and also has a "THX input", and while it does have five XLR inputs, this particular THX input isn't balanced... Or maybe this is yet another "THX input", but the one for plebs?

[Marco Giustini]

THX eventually turned into a marketing machine, I don't think it means anything today. But back then, it was a thing. Below the CP input for the 3417 crossover, the DC25 input was indeed balanced.

SCR-20260628-kckj.png

Surprisingly though, the outputs were unbalanced

SCR-20260628-kcym.png

[Gordon McLeod]

The surrounds and sub were unbalanced on the 3417

[Ryan Gallagher]

It turned out to only be a thought exercise. We got the deck re-laid and first coat of paint down today. I’ll have a surface for the C and LFE cabinets to roll out on as normal tomorrow night!

there is still a lot of clean up to do in the backstage areas, but the auditorium will be ready for a film audience.

i’ll still look at my options doing a downmix for such strangeness if it ever is needed.

[Rick Cohen]

Magna-Tech Electronic Co. sells a passive audio mixer board that safely combines the 5.1 analog output of any cinema processor into a 2.0 stereo output, mainly for drive-in applications that use stereo FM transmitters.

https://www.mteworld.com/

[Ryan Gallagher]

Magna-Tech Electronic Co. sells a passive audio mixer board that safely combines the 5.1 analog output of any cinema processor into a 2.0 stereo output, mainly for drive-in applications that use stereo FM transmitters.

https://www.mteworld.com/

Do you recall a product name? I'm not able to find anything similar using their website search.

[Rick Cohen]

Do you recall a product name? I'm not able to find anything similar using their website search.

Darco/Odyssey Products Model DI6-3-KIT/THX Drive-In Mixer Kit. It may be something they make to-order and I doubt they have it available off the shelf. Definitely a specialty item.

As a side note, the USL JSD-60 had this feature available internally, with just the click of the mouse. It's the perfect sound processor for a drive-in application.

[Ryan Gallagher]

Darco/Odyssey Products Model DI6-3-KIT/THX Drive-In Mixer Kit. It may be something they make to-order and I doubt they have it available off the shelf. Definitely a specialty item.

As a side note, the USL JSD-60 had this feature available internally, with just the click of the mouse. It's the perfect sound processor for a drive-in application.

cheers for the detail.

Could one in theory insert a JSD-60 with no EQ after the primary processor on the analog outputs just to get that mix down feature in a pinch? I happen to own one, so curious if that method is viable as well.