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Topic: Downmixing on CP650

Tim OBrien
Film Handler

Posts: 36
From: Vassar, MI /USA
Registered: Jan 2010

posted 01-24-2013 12:19 PM

I'm planning some outdoor movie shows using both film and digital (blu-ray) projection. Although we're typically limited to L, R (phantom center) and Sub channels I want to have the best audio possible. My thought was to run the 5.1 stream from the film reader and the discreet analog outputs from the BD player into a CP650. Is there any way to create a 2.1 downmix on the 650, or am I approaching this all wrong?

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Dennis Benjamin
Phenomenal Film Handler

Posts: 1445
From: Denton, MD
Registered: Feb 2002

posted 01-24-2013 02:02 PM

I am glad you brought this subject up. We use Dolby CP750s with our digital projection set up. We have run a few Blu-Rays that have only the DTS Master soundtrack on them. When we have this situation, we have had to down mix our sound to 2.1 stereo to run it through the processor, that's all the Blu-Ray offers if you cannot utilize the D.T.S. Soundtrack (on some discs).

Is there an affordable device that we can buy that would allow us to play a DTS mastered Blu-Ray in Surround Sound through our Dolby processor? I get that we are using a "Dolby" specific product and that's where the issue is (D.T.S. vs Dolby). I guess these film companies make deals with D.T.S.? Sometimes when you get the Blu-Ray/DVD combo packs, I notice that the DVD has a Dolby 5.1 soundtrack, but not the Blu-Ray. It's quite annoying.

Anyways...

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Tony Bandiera Jr
Film God

Posts: 3067
From: Moreland Idaho
Registered: Apr 2004

posted 01-24-2013 02:48 PM

Tim and Dennis there are two very simple solutions:

1) Buy or rent a mixing console with a minimum of twelve input channels and use it to downmix to either 2 or 3 channels. Bonus: If you have more than 12 input channels (or don't use the subs or surrounds, whatever is best at the time) you can also run a few mics for P.A. use as well. For example: 16 in x 2 out line level for $150. That one does NOT have mic preamps built in. Or: 16 x 2 with mic preamps for $230.

2: I have in the past built a passive device to "downmix" L/C/R into a single output using 10k resisters. (On a CP650/750 you can simply use the Hearing Impaired out to get the exact same effect. IIRC it is controlled by the main fader...but do a quick test first.)

Dennis: as for the DTS issue, best bet is to find a home receiver that has either pre-amp outs or a Toslink bitstream out since pretty much all of them do DTS decoding. Then, IIRC you can feed the Toslink out of the receiver directly into the CP750's Toslink input (I can't remember what protocol to select though..it might be Bitstream or Discrete. not sure at the moment.) I just did something like that on a recent install.

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Carsten Kurz
Film God

Posts: 4340
From: Cologne, NRW, Germany
Registered: Aug 2009

posted 01-24-2013 03:51 PM

quote: Tim OBrien
My thought was to run the 5.1 stream from the film reader and the discreet analog outputs from the BD player into a CP650. Is there any way to create a 2.1 downmix on the 650, or am I approaching this all wrong?

The easiest way to do this is probably to use a small analog mixer (Mackie, Yamaha, Behringer, etc.) connected to the CP650 analog multichannel out. That is, between CP650 and amps.

That way you can downmix/pan any incoming multichannel signal to a set of 2 or more output channels. These mixers go for as little as 50-100US$. They can also be used during the event to connect a microphone or music player.

Sure there is no way to accomodate at least an additional center speaker?

Even stereo mixers will usually allow to feed a third channel by using aux/monitor/fx send outputs.

- Carsten

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Tony Bandiera Jr
Film God

Posts: 3067
From: Moreland Idaho
Registered: Apr 2004

posted 01-24-2013 05:15 PM

quote: Carsten Kurz
The easiest way to do this is probably to use a small analog mixer (Mackie, Yamaha, Behringer, etc.) connected to the CP650 analog multichannel out. That is, between CP650 and amps.

Gee, why didn't someone else think of that? [Roll Eyes]

Oh, wait..someone did:

quote: me
1) Buy or rent a mixing console with a minimum of twelve input channels and use it to downmix to either 2 or 3 channels. Bonus: If you have more than 12 input channels (or don't use the subs or surrounds, whatever is best at the time) you can also run a few mics for P.A. use as well. For example: 16 in x 2 out line level for $150. That one does NOT have mic preamps built in. Or: 16 x 2 with mic preamps for $230.

Amazing, ain't it? [Big Grin]

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Carsten Kurz
Film God

Posts: 4340
From: Cologne, NRW, Germany
Registered: Aug 2009

posted 01-24-2013 06:57 PM

Sorry for wasting your time, Tony. I enjoyed it, though ;-)

Didn't know this forum is a being-first competition.

- Carsten

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Tony Bandiera Jr
Film God

Posts: 3067
From: Moreland Idaho
Registered: Apr 2004

posted 01-24-2013 06:59 PM

It's all good Carsten, I enjoyed it too. [Big Grin]

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Tim OBrien
Film Handler

Posts: 36
From: Vassar, MI /USA
Registered: Jan 2010

posted 01-24-2013 08:11 PM

Great minds think alike? Thanks for the tips, gentlemen.

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Manny Knowles
"What are these things and WHY are they BLUE???"

Posts: 4247
From: Bloomington, IN, USA
Registered: Feb 2002

posted 01-24-2013 09:40 PM

Tony, I interpreted your solution as meaning he should go from each device's outputs into the mixer -- hence the 12 inputs?

Carsten's solution wouldn't require 12 inputs -- only six.

For a permanent solution, I've seen the Soundweb London BLU-16 Signal Processor used at d-cinema drive-ins. But this would be overkill for the OP's temporary situation. I'm only including it in case some future person searches this thread.

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Tim OBrien
Film Handler

Posts: 36
From: Vassar, MI /USA
Registered: Jan 2010

posted 01-25-2013 06:53 AM

Manny, thanks for clarifying this as I was a bit confused. I know I need to do some homework as I've never used a mixer but the BSS product is a bit more intuitively appealing due to its flexibility. It seems I would need to combine the L and C outputs (from the 650) to become the left channel; and the R and C for the right channel. I can't see how this is possible on some of these mixers, but again, I'm in unfamiliar territory... And there's no such thing as overkill.

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Carsten Kurz
Film God

Posts: 4340
From: Cologne, NRW, Germany
Registered: Aug 2009

posted 01-25-2013 07:08 AM

Tim, get a manual or closeup photo for one of these cheap mixers, you will understand it very quickly.

Wether that mixer has 6 or 12 inputs - it doesn't matter as long as it fits your need and is available. These tiny things are sold in huge masses to musicians for home studio, you get great value for very little money.

Basically, you e.g. feed L to channel1, center to channel2, right to channel3.

The mixer mixes these into a stereo channel, which can be controlled by a master fader. The output from the master fader goes to your stereo amp and controls presentation volume.

Now, every input channel has a PAN or balance pot where you can decide, which amount of this input goes to the L or R output of the stereo master output.

For L, you have it set all counter clockwise to L only, for center you would have it 'center' for equal amounts to L and R out, for R fully clockwise to R output only.

That's it.

The input channels and sometimes also output channels usually have a simple equalizer or low/mid/high tone controls, so you can do slight(!) adjustments to the sound balance as well.

With the separate input faders, you can as well control the amount of center/dialog volume very easily to your needs.

And as I said, most mixers will probably also allow a separate feed out of the center channel to a separate center amp/speaker so you have a better solution than the phantom center.

The actual input layout of these mixers vary a little bit - some have 1-6 mono mic channels, + some stereo channels, but it actually doesn't matter as every mic channel will also accept line signals from the CP650. Doesn't matter wether you start with channel1 or channel 7.

Best is probably to get a mixer with at least 3 identical mono(mic) input channels, as it makes setup easier.

Wether it actually has faders or volume knobs on the channels is not important for this application.

http://www.bhphotovideo.com/c/product/421989-REG/Behringer_1202_XENYX_1202_12.html

- Carsten

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Manny Knowles
"What are these things and WHY are they BLUE???"

Posts: 4247
From: Bloomington, IN, USA
Registered: Feb 2002

posted 01-25-2013 09:48 AM

^^ I'll second this.

But why not include Ls, Rs and LFE and mix those in too?

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Louis Bornwasser
Film God

Posts: 4441
From: prospect ky usa
Registered: Mar 2005

posted 01-25-2013 10:51 AM

Manny: in fact you HAVE to. On the discrete digital mix, there is no bleed, so any effect not mixed in is completely lost. This includes the subs. Louis

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Scott Norwood
Film God

Posts: 8146
From: Boston, MA. USA (1774.21 miles northeast of Dallas)
Registered: Jun 99

posted 01-25-2013 10:54 AM

But he's using a separate subwoofer. Assuming that the CP650 is set to the correct crossover point, he should be able to feed that signal directly to the power amplifier for his subwoofer.

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Manny Knowles
"What are these things and WHY are they BLUE???"

Posts: 4247
From: Bloomington, IN, USA
Registered: Feb 2002

posted 01-25-2013 01:15 PM

I'd urge running LFE through the mixer -- the overall mix of the main channels will be affected, so I'd want an easy way to bring the LFE into balance with this "new" mix -- and to have its level follow any level changes made during show.

Oh, and to get dedicated center and subwoofer outputs, you'll need a mixer with 4 outputs (L/C/R/LFE). Most likely, the smallest compatible configuration for a mixer will be 8in/4out. You could use leftover inputs for mic and/or non-sync music.

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