Film-Tech Forum ARCHIVE: DCP Digital Sound Formats Question

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Posted by Mitchell Dvoskin (Member # 751) on 06-17-2012, 07:39 PM:

Pardon what may seem like a stupid question from one who has not yet directly dealt with digital cinema.

What digital format is the sound? Does the server output a bit stream comparable to a 35mm reader that can be fed into an existing Dolby Digital and/or DTS processor, or is it a new digital format, or does the server output the discreet channels directly in analog, or none of above?

Posted by Claude S. Ayakawa (Member # 1401) on 06-17-2012, 07:51 PM:

As a patron of the cinema and not a projectionist, I always wanted to know the same thing you had asked, Mitchell

-Claude

Posted by Terrence Meiczinger (Member # 5059) on 06-17-2012, 08:04 PM:

A DCP contains an MXF audio file. The MXF file holds discrete audio channels in uncompressed WAV PCM format. So, 7.1 audio is literally 8 channels, no encoding or compression.

Posted by Jock Blakley (Member # 6552) on 06-17-2012, 08:36 PM:

The discrete WAV files are then fed out of the server as a digital bitstream. Newer processors like the Dolby CP750 can accept this directly, but older processors can't so a DAC is used to convert the AES/EBU stream to an analogue signal that uses the same connection standard as DTS and so is accepted by the External 6-Track input on your processor of choice.

Since we use both DTS and D-Cinema (albeit DTS very rarely) we have a switcher that allows us to change between DCI and DTS from the front of the rack rather than continually switching the DB25 plugs at the back of the CP500.

Posted by Claude S. Ayakawa (Member # 1401) on 06-17-2012, 08:39 PM:

So a MXF audio file is a totally new digital sound format making Dolby, DTS and SDDS sound processors obsolete with digital cinema. Am I correct to assume this?

-Claude

Posted by Jock Blakley (Member # 6552) on 06-18-2012, 11:17 AM:

MXF stands for Material Exchange Format and isn't specifically a type of audio file - instead it's simply a container for other files. Think of it as a box that is made to precise standards and can be opened by anybody who knows how.

A DCP contains two MXF files - one for audio and one for picture.

The audio MXF contains anywhere between 1 and 16 audio tracks, with one discrete track for each channel (in the same way that 70mm had discrete tracks rather than a matrix like optical Dolby Stereo). Each of these tracks is in the Broadcast Wave format (BWFF) with linear pulse-code modulation (LPCM). This is far from a totally new format - BWFF was first defined by the European Broadcasting Union in 1997 and is derived from the Waveform Audio File Format (WAV) that we all know and love and thank Microsoft and IBM for all the way back in 1991, and the PCM encoding dates to 1972.

The picture MXF file contains every frame of the film* stored each as an individual JPEG2000 file.

( * = or every frame of that particular "reel", but that's an unnecessary complication right now)

As to obsolescence though - yes, your DTS-6D will be obsolete on the same day your Cinemeccanica or Century or Simplex or Christie or Philips or Kinoton becomes obsolete.

I can't speak for SDDS because I have zero experience with the system and zero knowledge of the capabilities of its processors.

Basically though any film-only sound decoder or processor or playback system will be irrelevant in a digital-only cinema for very obvious and unsurprising reasons. Dolby's later processors will remain relevant even if you completely ignore the film options because, as I mentioned before, the D-Cinema server's AES/EBU sound output is directly accepted by the CP750 and can be very easily adapted for the External 6-Track (Format 11) input on the CP500 and CP650, as well as certain earlier models. Doremi supply their AUD-D2A unit expressly for this purpose and I imagine other vendors have such a unit too.

If SDDS processors ever had six-track-in for DTS than the same point stands for them.

Posted by Mitchell Dvoskin (Member # 751) on 06-18-2012, 07:52 PM:

Thank You.

Posted by Tony Bandiera Jr (Member # 2365) on 06-18-2012, 09:55 PM:

quote:
the D-Cinema server's AES/EBU sound output is directly accepted by the CP750 and can be very easily adapted for the External 6-Track (Format 11) input on the CP500 and CP650,

You do NOT need to use an outboard adapter for the CP650, you just need the CAT 790 Card. It will then accept the AES/EBU bitstreams directly.

That leaves your external 6-channel input available for other uses.

The only known drawback to the CAT 790 approach is that evidently some CP650/CAT790 combos can get a fit of "Robo-sound" on occasion. So far I haven't encountered it although others here have.

EDIT: See THIS THREAD

Posted by Jock Blakley (Member # 6552) on 06-18-2012, 11:25 PM:

Ah, very true Tony, I mentally changed "can cause robosound" to "not possible" without realising.

Posted by Monte L Fullmer (Member # 2797) on 06-18-2012, 11:59 PM:

Other processors can use the USL eci60 interface unit to convert the digital stream into 6 channel analog to work with their aux 6 channel input setups.

CP500's will then use "Format 11" - the same format that DTS used.

Posted by John Wilson (Member # 269) on 06-19-2012, 12:34 AM:

A weekly re-boot of the 650 seems to keep ROBOSOUND at bay.

Posted by Brad Miller (Member # 2) on 06-19-2012, 02:25 AM:

Nope, not so John. I tried everything possible to prevent the ROBO SOUND on a 650. I have tried:

Never turning the 650 off
Powering the 650 off overnight
Power cycling the 650 off for 5 minutes at the end of each show

The more power cycles it was given, the more frequent ROBO SOUND attacked me.

Screw it...Format 11 to the rescue!
[thumbsup]

Posted by Jock Blakley (Member # 6552) on 06-19-2012, 04:27 AM:

quote:
Format 11 to the rescue!

Too true - although in our case it's more because it'd be a tad painful to replace our CP500-70 for the same amount of convenience and rack-space.

Posted by Scott Jentsch (Member # 1681) on 06-25-2012, 09:47 AM:

I knew that the audio was PCM, but I'm surprised that it is not losslessly compressed in any way.

Maybe they feel that there's more hard drive space right now than there are CPU cycles to decode a compressed stream, but I see this as something that will most likely change in the foreseeable future.

Posted by Jock Blakley (Member # 6552) on 06-25-2012, 07:04 PM:

Why would that be, Scott?

Already the soundtrack represents only a fraction of the storage and processor-time requirement relative to the picture, and that gap is only going to increase as resolution and frame-rates climb.

Posted by Carsten Kurz (Member # 5396) on 06-25-2012, 08:06 PM:

Lossless compression adds complexity and needs standards - all other DCP aspects use common standards - like Broadcast Wave Format for audio. Adding compression Is just not worth the effort. Lossless audio compression yields low compression ratios, like 2:1.

A typical 5.1 audio track in a standard feature will have something like 5GBytes of e.g. 150Gbytes total. What's the point in reducing this to 2.5Gbytes of 150Gbytes total? Most DCP shipping drives are larger than needed anyway, 320GB becoming a rare species.

- Carsten

Posted by Scott Jentsch (Member # 1681) on 06-27-2012, 11:48 AM:

For some reason, I was thinking that lossless compression was higher than 2:1, but some quick looking shows that I was mistaken.

Even though something like FLAC compression is a widespread standard, has MD5 hashes to ensure data integrity, and requires little decoding horsepower, it makes sense that the end result probably doesn't justify the effort.

Posted by Bobby Henderson (Member # 840) on 06-27-2012, 12:59 PM:

As others have said, lossless compression isn't necessary for the audio tracks on DCP hard discs. Storage space is ample.

I'm sure Dolby and DTS would have loved it if d-cinema employed lossless compression. Dolby and DTS would have had a chance to apply their TrueHD and DTS-MA compression schemes and brand names to the audio track. But that might have brought about yet another format war or created a situation where the DCP was carrying the movie audio track in both Dolby TrueHD and DTS-HD Master Audio. The dual inventory audio would eat up just as much disc space as an uncompressed LPCM soundtrack. The craziness might not even stop there. Dolby TrueHD and DTS-HD Master Audio are the most well known lossless surround sound formats for home theater. What if some jackass insisted the DCP carry dupes of the soundtrack in other formats like FLAC and Apple Lossless too?

Uncompressed linear PCM doesn't have a cool brand name and pretty much has a generic vibe. But it's more compatible than anything else. One thing I do wonder about is limitations from one d-cinema setup to another in handling high bandwidth LPCM, like 24-bit 96kHz audio or even 24-bit 192kHz.

If Dolby Atmos takes off in popularity that will make it necessary for the DCP to carry dual inventories of the audio (LPCM 5.1 and Atmos).

Posted by Scott Jentsch (Member # 1681) on 07-06-2012, 12:54 PM:

It's unfortunate that some sort of de facto moniker is not attached to it, so that it would be easy to market. It's somewhat ironic that the most superior sound format available has no marketing attached to it, effectively blunting its marketability.

Even if it was called what it is, it would be something. Some theaters were inserting it into the notes on their showtimes as LPCM 7.1 or PCM 7.1, but none are right now. (Only two theaters are advertising ATMOS)

Posted by Jonathan Goeldner (Member # 4854) on 07-06-2012, 05:07 PM:

quote: Scott Jentsch
I knew that the audio was PCM, but I'm surprised that it is not losslessly compressed in any way.

Maybe they feel that there's more hard drive space right now than there are CPU cycles to decode a compressed stream, but I see this as something that will most likely change in the foreseeable future.

in terms of the lossless audio, the audio/soundmix of 'Saw 3D' was exceedingly dynamic - during the ear assaulting car explosion I literally thought the speakers blew as well. The underwater quake in 'Piranha 3D' it actually sounded like a ceiling brace in the auditorium had cracked too - it was both startling AND scary. The wide dynamic range that DCP's can deliver is outstanding in my opinion.

Posted by Ron Funderburg (Member # 4561) on 07-06-2012, 05:21 PM:

Scott most places market the sound by what the processor is that is being fed to. If the processor is Dolby then they say it is Dolby Sound if it is a DTS unit it is advertised as either DTS or Data Sat. I guess Dolby has come out with a new system but it isn't in many markets yet. I don't even know if there is a separate audio file for the new Dolby.

Posted by David Graham Rose (Member # 1450) on 07-07-2012, 02:11 AM:

Greetings All

I believe Bobby is mistaken with regard to the Atmos system. The whole point of Atmos is that dual inventory DCP's are not needed, and metadata is used to control the system which can be encoded onto a standard DCP with a 5.1 or 7.1 mix (which incidentally is generated from the Atmos mix). Or at least that's my limited understanding. Also for all those interested, I had my right foot amputated on Thursday following an incident with my former wife's lawnmower. The grass in the garden is now long, and I am a little lopsided. Can anyone make an "extension platform" to my right shoes?

From a wet Cambridge, I bid you Goodmorning

David.

Posted by Ron Funderburg (Member # 4561) on 07-07-2012, 10:06 AM:

David sorry to hear that hope you have quick recovery and get a good prosthetic (sp).

Posted by David Graham Rose (Member # 1450) on 07-07-2012, 01:30 PM:

Greetings to you Ron

I'm not that worried about that foot anyway as the arthritis was pretty bad in it as well and had long lost the feeling in my toes as well, so not too much of a disaster! I'll live to research further topics of interest! I suppose it's quite apt whist on the topic of Atmos and DCP's: Single inventory - good (i.e. my remaining foot); Dual inventory - bad (Thursday morning before the accident)!.

From a wet Cambridge, I bid you Good Evening.

David

Posted by Ron Funderburg (Member # 4561) on 07-07-2012, 01:34 PM:

I had major emergency (almost died) surgery on the 3rd of may. The recovery has been slow since it was a full open up your gut. Getting back to normal but have to follow restrictions until sometime in August. Can't tell you how hard it is not to go up the stairs to the booth.

Posted by David Graham Rose (Member # 1450) on 07-08-2012, 02:26 AM:

Greetings Ron

Get well soon I say! And don't overdo it. I've just hired a gardener.

David

Posted by Yinghong Wu (Member # 6908) on 07-09-2012, 03:09 AM:

I use OpenDcp to make the DCP,The sound format I use is 24bit,48KHZ,linear PCM audio.

Posted by Jonathan Goeldner (Member # 4854) on 07-09-2012, 10:13 PM:

didn't I read somewhere recently that Dolby is trying to get the studios/mixers to encode sound at 96khz ?

Posted by Jock Blakley (Member # 6552) on 07-10-2012, 02:46 AM:

The DCI standards do allow for 96 kHz sound in DCPs but it's up to people to use that capability.

Posted by Michael Brown (Member # 890) on 07-10-2012, 05:57 PM:

quote: Scott Jentsch
It's unfortunate that some sort of de facto moniker is not attached to it, so that it would be easy to market. It's somewhat ironic that the most superior sound format available has no marketing attached to it, effectively blunting its marketability.

Even if it was called what it is, it would be something. Some theaters were inserting it into the notes on their showtimes as LPCM 7.1 or PCM 7.1, but none are right now. (Only two theaters are advertising ATMOS)

One of the large chains on the UK is advertising it as Dolby 'Profound Sound'

..and if you read the blurb on their website is seems to suggest as well as making up the name they also seem to take credit themselves for the mix.

"Breatht4King Vue is further enhanced with Vue Profound Sound, in stunning Dolby 7:1 sound. Vue's unique and professionally mixed sound will make cinema goers feel like they are part of the action"

When in doubt just make something up. [Big Grin]

Posted by Jonathan Goeldner (Member # 4854) on 12-17-2012, 11:38 PM:

I heard a little news tidbit that Sony HAD released a film this year at 96kHz but I can't find any info on what movie that was... ???

Posted by Grant Chambers (Member # 7051) on 12-23-2012, 01:23 AM:

The .wav files inside a DCP are 24 bit. 48000 khz mono tracks assigned specifically to each speaker speaker speaker (if it is indeed a surround sound feature)

Posted by Bobby Henderson (Member # 840) on 12-27-2012, 09:57 PM:

I don't know why movie studios wouldn't try 24-bit 96kHz audio on some releases, particularly ones that have a great deal of music in them.

There's more than a few Blu-ray disc releases featuring 5.1 or 7.1 audio in 24-bit 96kHz resolution per channel. Baraka is one disc that immediately comes to mind. Quite a few concert discs have 24-bit 96kHz audio. If 24/96 resolution audio is good enough for the home it damned sure ought to be good enough for the commercial movie theater. Hell, Blu-ray (as well as the defunct DVD Audio format) supports 2 channel 24-bit 192kHz audio.

Posted by Antti Nayha (Member # 4980) on 12-28-2012, 03:35 AM:

You won’t hear a difference between 48 kHz and higher sampling rates. The 24/96 home formats are just audiophile snake oil nonsense.

Posted by Marcel Birgelen (Member # 6801) on 12-28-2012, 07:43 AM:

quote: Antti Nayha
The 24/96 home formats are just audiophile snake oil nonsense.

But if you rub your digital interlink cables in said snake oil at least once a week you can FEEL the difference, at least between your ears. [Smile]

Posted by Chris Slycord (Member # 4239) on 12-28-2012, 05:22 PM:

Or, as Brad once informed me an audiophile theater goer told him, if you got the wire pointing the right direction (and presumably in the oil) it'll sound better.

Posted by Mike Blakesley (Member # 26) on 12-28-2012, 06:06 PM:

quote: Brad Miller
Never turning the 650 off
Powering the 650 off overnight
Power cycling the 650 off for 5 minutes at the end of each show

So this brings up a question...

We've already decided (well most of us) that it's best to never turn off servers. What about a Dolby processor? I've always turned our CP650 off every night figuring there aren't really any moving parts in it that are going to wear out (like hard drives) on boot-up. But is it better to leave it on? For that matter, what about amplifiers?

Posted by Marcel Birgelen (Member # 6801) on 12-28-2012, 07:00 PM:

quote: Chris Slycord
Or, as Brad once informed me an audiophile theater goer told him, if you got the wire pointing the right direction (and presumably in the oil) it'll sound better.

Sure, that's because if the electrons hit the end of the wire at an angle, that will cause some minor disturbance in the electromagnetic force that only a gifted audiophile will be able to detect [Wink]

quote: Mike Blakesley
We've already decided (well most of us) that it's best to never turn off servers. What about a Dolby processor? I've always turned our CP650 off every night figuring there aren't really any moving parts in it that are going to wear out (like hard drives) on boot-up. But is it better to leave it on? For that matter, what about amplifiers?

I'm still trying to figure out why so many people think that their equipment will last longer, if they never turn it off...

And just like the CP650, much of the other equipment does have some minor moving parts in it: fans. Those things will eventually wear out. Not to forget, your equipment will even collect more dust if those things are sucking in air.

Even regarding servers, there is much discussion about how much damage a spin down/spin up cycle actually does. One thing for sure, a powered down disk is at least not wearing out its drive mechanism [Wink]

. Servers DO need a clean shutdown, or else you risk data corruption of course. So just switching them off is really a no go. From my personal experience, I sometimes see that an old disk that has been turning non-stop for a year or two will refuse to spin up after a power cycle. But usually, you will update your system more frequently than that, so you will probably run into those problems earlier.

But you know what's great about regular power cycles? You know that your stuff will work, even after the power has gone out unexpectedly. I've already encountered many setups that won't "boot up" after someone or something pulled the plug.

Another thing is that many of those modern digital gadgets have the tendency to need a reset from time to time to get rid of some messed up internal state that will show up as a nasty bug later on. With every power cycle you'll give them a free reset.

Posted by Mike Blakesley (Member # 26) on 12-28-2012, 08:43 PM:

quote: Marcel Birgelen
Even regarding servers, there is much discussion about how much damage a spin down/spin up cycle actually does.

Well....of course this is totally unscientific, but here's some recent experience from me:

My list of computers includes:
- A GDC digital cinema server with a RAID (3 hard drives)
- A cheap-ass Gateway office computer
- A Partner 2000 concession computer
- Four HP and two Dell computers at my day job

The server, originally, was powered down every night. All the other machines were left running constantly.

The Partner had its touchscreen go out after seven years of operation, but the drive is still fine. The Gateway ran for nine years, trouble free until we finally replaced it due to being outmoded. When we took it out of service the hard disk was still functioning.

The four HP machines at my day job have never lost a day yet after five years of operation. The two Dell machines both worked for nine years. One finally was felled by viruses so we decided to replace both; the hard drives were still working fine.

In the server, which was shut down nightly, we had a hard drive failure after 29 months. GDC, to their credit, replaced all three hard drives in the RAID even though the machine was five months out of warranty.

So now we leave the server running all the time.

Like I said this is completely unscientific so your mileage may vary.

Posted by Steve Guttag (Member # 268) on 12-28-2012, 09:47 PM:

5 will get you 10 that the failed HDD in your GDC were the dreaded Seagate "ES" series drives...they would fail regardless of your power cycle method.

I don't run the sound systems 24-hours and most things with fans I like to shut off. The servers are the big exception for me...I've had better luck leaving them powered 24-hours. That also allows for updates during the down time. The need to update a sound processor is far less than a server.

Posted by Marcel Birgelen (Member # 6801) on 12-30-2012, 04:03 AM:

quote:
Well....of course this is totally unscientific, but here's some recent experience from me:

I guess that's the big problem here. Everybody has their own experiences, but there isn't very much scientific data available on this subject.

There was a very interesting study about hard drive reliability a while back published by Google. Although, this study didn't really include spin-up/spin-down cycles, because most of their disks are supposed to be always on-line and spinning.

Personally, I tend to keep everything called "server" on-line 24/7, but the rest should really be switched off if it isn't being used for a few hours. Besides saving your equipment and power, you're also largely eliminating another fire hazard.