Film-Tech Forum ARCHIVE: DCI Audio on the cheap

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Posted by David Buckley (Member # 2600) on 08-12-2014, 06:01 PM:

It looks like our little Town Hall may be getting a DCI projection system, but funding for audio is a problem. We're going to have to use an existing audio system with some band-aids. So...

a) Is there a processor of lower cost that the CP750 that isn't absolute pants? The film projectors are gone, so its for DCI only.

b) Audio looks like being 3.1, ie LCR plus sub. Assuming the processor outputs 5.1, what do I do with the surround channels? Or is this a problem the processor can solve and it outputs 5.1 downmixed to 3.1?

I'm hoping that next year we'll get some funding so I can improve matters, so no surrounds may not be a permanent problem.

Thanks!

Posted by Brad Miller (Member # 2) on 08-12-2014, 06:27 PM:

What processor are you currently using?

Posted by Marcel Birgelen (Member # 6801) on 08-12-2014, 06:34 PM:

If you really don't want to invest in a Digital Audio Processor, you could try to get a Doremi AUD-D2A, which will convert any "standard" 8-channel AES/EBU signal to 8 discrete analog audio signals and hook it up to some kind of home-cinema amp/receiver/audio processor.

Downmixing for the missing channels still needs to be done by the audio processor, but many cheapo home-cinema amp/receiver/processor combos offer those features.

Still, it's best to try to get a professional cinema processor from Dolby or Datasat, alongside with somebody who actually knows how to calibrate those things.

Why not try the refurb market too? A used Dolby CP650 can be bought for as little as USD 1500.

Please note: A CP650 will not downmix your channels, you still need something else for that, like a mixing console with sufficient channels (can also be bought cheap).

Posted by Tim Sherman (Member # 569) on 08-12-2014, 06:36 PM:

just go with a USL JSD-60

Posted by Carsten Kurz (Member # 5396) on 08-12-2014, 06:51 PM:

Second Hand DTS XD10P can be found for little money as well.

Any amps, speakers, etc. already there?

You can connect an AUD-D2A to a small mixing desk, around 100US$ for a suitable type, but to do EQ and proper mixdown during daily operations needs a trained operator or a clear 'don't touch it!' statement.

I'm currently trying to use a medium-class homevideo receiver in a very minimal DCI setup with LCR only. Seems to work, unfortunately there is no cheap way from 5.1 AES to HDMI, so, for now I need to use an AUD-D2A and discrete analog INs. But it also allows to connect a BluRay Player, etc. without the complications of a mixing desk, and there is a simple cinema processor type master volume control.

I payed around 300€ for this Marantz receiver. You can use the internal amps for very small rooms, or use the pre-outs to 'real' external amps.

I hope at some point there will be an affordable 6-8ch AES->HDMI audio converter for a full digital solution.

- Carsten

Posted by Harold Hallikainen (Member # 5405) on 08-12-2014, 07:02 PM:

Since Tim mentioned the USL JSD-60, I'll second that. It has user-configurable channel mixing (including mixing down to stereo for drive-ins). So, you can pretty much make it do whatever you want.

Harold

Posted by Carsten Kurz (Member # 5396) on 08-12-2014, 07:10 PM:

Didn't know about the downmix option on the JSD-60. Nice feature.

- Carsten

Posted by Harold Hallikainen (Member # 5405) on 08-12-2014, 07:44 PM:

Thanks! We wanted flexibility in channel routing. Working with our DSP guy, we kept coming up with more and more routing options. It just became too much to do with software input select switches. We finally decided to make it generic. Each processing channel gets the sum of products of incoming audio from every input times a mix coefficient. In most cases, the mix coefficient is 1.0 or 0.0, but it can be any floating point number. Pressing a button on the front or through automation just loads the saved mix coefficients for that format. It's working out well, including handling stuff I did not think of.

Harold

Posted by Mark Gulbrandsen (Member # 72) on 08-13-2014, 01:30 PM:

Yes, the JSD-60 is extremely flexible and I highly recommend it. If you think you might need a little more flexibility in terms of inputs, both analog and digital then the JSD-100 is the way to go.

Mark

Posted by Ken Lackner (Member # 1002) on 08-13-2014, 01:34 PM:

JSD-60 was my first thought for new equipment as well. Agreed with Mark's comments about added options on the JSD-100, but it doesn't offer downmixing.

Posted by David Buckley (Member # 2600) on 08-13-2014, 05:28 PM:

Thank you gentlemen for your suggestions.

To answer Brad's question, the currently installed processor is "none".

The JSD-60 really had me going for quite a while, until I discovered the flaw. Which isn't the boxes fault, but an artifact of the sound system we'll be forced to use, for a while at least, which appears to have reduced in specification since my first post!

The audio system will be stereo, with a pair of speakers and a single mono sub, and the sub will need to have the bass end of the crossed over stereo speakers, as well as the LFE channel. The JSD requires (best as I can tell!) that if the screen speakers are biamped, then they are "properly" biamped, not just all the low end mixed to a single subwoofer channel. I see why they've done this with the crossover card, as it means there can be an analogue backup if the DSP quits, which is deviously clever in its own right.

But that feature makes it an incomplete solution; I'd need then to manage externally mixing multiple crossed over signals, which isn't the end of the world. But it does look like a good upgrade pathway for the future.

Unfortunately, used equipment is out, as the public money funding doesn't permit that.

Which brings me to the suggested Doremi AUD-D2A, which looks like the answer, for a while at least. In a similar vein I found the USL DAX-802, are there any pros / cons that make either of this more or less preferable than the other?

Posted by Harold Hallikainen (Member # 5405) on 08-13-2014, 08:04 PM:

If I understand your application, I still think the JSD-60 could do what you want. It sounds like you want to use the LFE for the low end of the screen channels. You can do that my telling the mixer to add L, C, R, and LFE with appropriate levels. The LFE output has the SMPTE specified 125Hz LPF, so high frequency stuff from the other channels won't get out.

Harold

Posted by David Buckley (Member # 2600) on 08-13-2014, 10:21 PM:

That is very clever, I didn't get that from the manual or from playing with the windows programming tool. Back on the list then! I guess it will come down to the price difference between the processor and straight DtoA.

Later... I've just had a play with the GUI, so I set the config as 5.1 biamp, use the advanced tab mixer to feed multiple channels to LFE, and in the crossover, set it to match the speaker crossover point, and then the high band comes out the standard outputs?

Posted by Harold Hallikainen (Member # 5405) on 08-13-2014, 10:45 PM:

Are you indeed going to run biamp on the screen channels? If not, just select 5.1. The LFE has an LPF in it. Also, all channels have a configurable channel filter (HPF, LPF, BPF, or notch).

Harold

Posted by David Buckley (Member # 2600) on 08-13-2014, 11:01 PM:

Yes, I see that now [Smile]

Posted by Ken Lackner (Member # 1002) on 08-14-2014, 10:07 AM:

quote: David Buckley
To answer Brad's question, the currently installed processor is "none".

If that's the case, then you will need one, and Doremi's or USL's D-to-A converters will not be sufficient by themselves. Since you must buy used equiment, any new cinema processor sold today will include AES decoding, so you don't need an external D-to-A converter.

I admit, I don't have much experience working "outside the box" with non-traditional cinema sound systems. Why are you needing to feed the LF from the screen channels to the subwoofer?

Posted by Jarod Reddig (Member # 6363) on 08-14-2014, 11:40 AM:

Enpar makes a cheap DCI processor you could look into on the used market. How cheap I am not sure.

http://www.cinetech.cn/product/227.shtml

Posted by Ken Lackner (Member # 1002) on 08-14-2014, 11:55 AM:

quote:
...and features convenience, flexibility, high reliability, excellent performance and ect.

Whew. Glad to know it includes ect. That's hard to find these days.

Am also happy to see the unit has adopted Humanized computer-based interfacial operation. That's such an important thing to have in a processor.

Posted by Gordon McLeod (Member # 33) on 08-14-2014, 02:33 PM:

Smells alot like someone copied the USL product

Posted by Marcel Birgelen (Member # 6801) on 08-14-2014, 05:50 PM:

quote: David Buckley
Which brings me to the suggested Doremi AUD-D2A, which looks like the answer, for a while at least. In a similar vein I found the USL DAX-802, are there any pros / cons that make either of this more or less preferable than the other?

I don't have any hands on experience with the USL DAX-802. The quick specs mention downmixing capabilities for stereo and mono sound systems, but I don't know if it will handle crossovers like you need. It comes with an Ethernet port for management and firmware updates. It seems to do a lot more than the AUD-D2A.

The AUD-D2A excels in simplicity. It has one button: the power button. Furthermore it has just two ports: AES/EBU in, Analog audio out. There is nothing to configure.

There are two versions though, one with a balanced and one with an unbalanced audio output. The unbalanced version seems to be the default, but be sure to get the right version for your setup to avoid unnecessary wiring complexity.

quote: Ken Lackner
If that's the case, then you will need one, and Doremi's or USL's D-to-A converters will not be sufficient by themselves. Since you must buy used equiment, any new cinema processor sold today will include AES decoding, so you don't need an external D-to-A converter.

He explicitly mentioned that used equipment is out of the question, because public money is involved and the rules and regulations don't allow for that. Something that's quite common.

Furthermore, why do you still need a "cinema processor", once you got the analog audio channels from the PCM streams? Sure, a cinema processor wraps all those fancy equalization and calibration features you need in a single package, but if you go DIY, all you need is amps and preferably something to do some equalizing and mixing.

quote: Ken Lackner
Why are you needing to feed the LF from the screen channels to the subwoofer?

I suppose those LR speakers are not your average cinema speakers.

quote: Gordon McLeod
Smells alot like someone copied the USL product

It probably comes with that signature burned transistors and exploded capacitors smell included...

They also feature an Optional 8-16channel AES-EBU digital input. Sounds strange that such an essential part would be optional [Wink]

.

For something purely digital on a shoestring budget and limited use, yeah, maybe you could try some Chinese copycat. But for something that generates or processes analog signals, you should really stay away from cheapo copycat ChinaTech(tm) products.

Posted by Ken Lackner (Member # 1002) on 08-15-2014, 08:03 AM:

Holy typo, Batman! I totally meant must buy NEW equipment. Kinda changes the meaning a tad, huh?

Whoops.

Posted by Marin Zorica (Member # 1716) on 08-15-2014, 05:15 PM:

Or, you can use some cheap D/A converters and audio mixer, since you said it's going to be only stereo with sub? In that case i would do this.....put L to L speaker, and same with R channel, center to both L and R speakers, and sub to sub......

I used similar setup quite couple of times, even i have some AUD-D2A from doremi, they are not much better that some small china D/A converter......to be honest, i found D/A to be quite noisy!

Posted by Carsten Kurz (Member # 5396) on 08-15-2014, 07:43 PM:

A couple of those cheap china S/P-DIF converters make a nice and cheap backup for your cinema processor in case of a failure. I always have a few in the drawer.

Add a 50€ analog mini-mixer, and you're back on track with L/C/R and mono surround.

- Carsten

Posted by Harold Hallikainen (Member # 5405) on 08-15-2014, 10:24 PM:

Backup equipment is certainly great to have on hand! Note that the JSD-60 (and other USL processors) have a "bypass function" that does D/A, input switching, front panel format and level control, etc. It's totally separate circuitry except for the small processor running the front panel.

For this particular installation, it's certainly possible to use a DAC and mixer. But you don't get EQ, sync delay, input selection, and it's a bit of a kludge. So, I suggest the JSD-60 (but I'm part of the design team).

Good luck!

Harold

Posted by Mark Gulbrandsen (Member # 72) on 08-16-2014, 11:05 AM:

quote: Jarod Reddig
Enpar makes a cheap DCI processor you could look into on the used market. How cheap I am not sure.

If the Enpar D to A is anything at all like their speakers run far far away as fast as you can! I installed one pair at a customers request because they were cheap. I ended up taking them back out and replacing them with QSC speakers. A cheap price is not worth the hassle you're gong to have with their stuff down the road.

Mark

Posted by Jarod Reddig (Member # 6363) on 08-16-2014, 07:11 PM:

I can't speak for they're durability but there's one installed at my local 8 plex that replaced a QSL processor in there best sounding room. The QSL unit had been there for years and if hadn't of peeked in the booth I would still have thought the QSL processor was installed.

Posted by Carsten Kurz (Member # 5396) on 08-16-2014, 07:20 PM:

Thanks Harold. Always wondered about the specific design approach for useful bypass mode circuitry on digital processors.

- Carsten

Posted by Jarod Reddig (Member # 6363) on 08-16-2014, 08:26 PM:

Sorry I meant a USL processor in my last post just for correction.

Posted by David Buckley (Member # 2600) on 08-17-2014, 06:03 AM:

Thanks All

I've recommended the JSD-60, it may be a tad more than is strictly required now, but if we get around to upgrading beyond 2.1 then it will be nice not having to gang many volume controls in some external mechanism.

So now... we wait and see......

Posted by Brad Miller (Member # 2) on 08-17-2014, 02:32 PM:

Remember when DCI standards meant something? Everyone was to have true 5.1 and 14fl of light, etc no matter what.

Now we have people all over the place folding down the audio, grossly under lighting their screens. It's just awesome.

Posted by Steve Guttag (Member # 268) on 08-17-2014, 03:41 PM:

They only meant something when there was an enforcement mechanism (kind of like THX). And, in truth, despite the VPF thing, Cinemark proved that they could get around the 5.1 requirement anyway and did mixdowns on some of their theatres anyway. The 14fL was always the target light...as others have hammered on, since the permissible range is down to 11fL...there is no violation there and movies should be just as good at 11fL since that spec would have been checked to be just fine.

Posted by Martin McCaffery (Member # 37) on 08-17-2014, 04:01 PM:

quote: Brad Miller
Now we have people all over the place folding down the audio, grossly under lighting their screens. It's just awesome.

Turns out digital is just like film afterall [evil]

Posted by David Buckley (Member # 2600) on 08-17-2014, 04:19 PM:

Guilty as charged!

In my defense, The plan says to go to 5.1 (or 7.1?), but in community cinema, it is always a question of money. Our first digital season (ie 2014/2015, we haven't traditionally presented over summer), the community can have movies in stereo, or no movies at all.

Given that what the community got in the good old days was 35mm changeovers with relatively unskilled amateur operators, from prints that have already had their run (or two!) in the hands of the multiplex operators, through our old sound system, then they will get better picture and sound than they used to enjoy.

The only way is up!