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Author
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Topic: Modern Surround Sound?
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Mike Elliott
Film Handler
Posts: 3
From: Pittsburgh, PA, USA
Registered: Sep 2018
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posted 09-26-2018 02:29 AM
Hi everyone, hope this is the right forum for this as film-tech kept popping up everywhere I looked! If not, feel free to redirect me.
So I am AV systems engineer for a university and am typically charged with the audio aspects of our systems, especially in more complex one-off kind of situations. Recently, funding was procured to update most of the tech for a large, multi-purpose, auditorium space. One of the use case's for this space is to show feature films several weeks after they have aired in commercial theaters.
While most of the space is getting upgraded, the current speaker system (older JBL units) and the cinema projector (Sony SRX R320) are staying given funding limits. What I am trying to wrestle with is how surround sound is handled at the cinema level now and days. Last time I looked at surround with any depth was over a decade ago.
Now I have inquired with the organization responsible for handling the SRX R320 and the matching media server (LMT 300?) , but being a student organization, their knowledge has proven very limited. The best info I have gotten from them is their DCP usually have both 5.1 and 7.1, but can only use the 5.1 due to system limitations.
I know the media server outputs uncompressed PCM audio over AES at 24/96. They are currently using some sort of Odyssey board or breakout to connect the LMT-300 to a CP650 (haven't been told how they are doing that yet).
All that said, my question is this...with modern digital cinema, do we even need a surround sound decoder like the CP650?
When I see "raw, uncompressed, linear PCM" that tells me (as someone with originally a recording studio background) that I do not need to decode the signals. Just route them to the appropriate speakers.
The reason I ask is the film aspect of the space is maybe, 10% of the use cases. The other 90% is events, classes, drama performances, etc.
In order to streamline the audio system we are trying to avoid having a dedicated cinema processor. The main audio processor will already have the necessary crossovers, time delays, EQ, etc (Tesira Server I/O) and is highly configurable. Trying to squeeze in say a QSC DCP 300 would convolute the processing and routing of the audio considerably.
I really can't seem to find any solid source of information on this topic. Is there something I am missing with modern d-cinema? Or is encoded surround not really a thing anymore at the cinema level unless you are doing say Atmos?
Thanks a bunch for any information!
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Marcel Birgelen
Film God
Posts: 3357
From: Maastricht, Limburg, Netherlands
Registered: Feb 2012
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posted 09-26-2018 04:22 AM
The decoded sound from a 5.1 or 7.1 DCP is really nothing more than standard PCM sound in multiple channels. Please notice that there are more than just the 7 main channels and the LFE channel in many DCPs, including the HI/VI channels and for some releases feature tracks like "motion code", which is being used by systems like D-BOX (the rocking cinema seats).
Your Digital Cinema Server usually outputs those channels using an industry standard AES interface (2 channels per AES signal), although the type of connector and wiring diagram is dependent on the manufacturer.
Now, although all those tracks are essentially just PCM tracks, there is a specific way of how they are mixed and it will only sound right, if you calibrate your room accordingly.
You don't specifically need a cinema processor like the Dolby CP650 or the more current CP750, the Datasat AP20/AP25 to "decode" those tracks, but the reason why those devices are still commonly being used is because they provide simple "out-of-the-box" solutions that get the job done and are specifically targeted at the niche of cinema.
In the end, those "all-digital" cinema processors do nothing you cannot do with any other pro-audio gear. In essence their functionality is:
- Audio and in some cases also video source switching
- Equalization, in some cases with "automatic calibration features", doing a lot of the legwork
- Insertion of delays, if necessary
- Digital to Analog conversion
Also, those standard cinema processors usually integrate easily with the automation in the cinema server.
So, can you do without e.g. a CP650 or CP750? Sure, you can. Some of the more recent installations skip the "old school" cinema processor and route multiple rooms through a QSC Q-Sys setup for example. You could replace the Q-Sys with any other advanced audio processing and switching platform.
In the end though, no matter what system you choose, it will be helpful to let an experienced cinema tech have a look at your setup, in order to correctly calibrate the sound in the room. You can try to do that yourself and with sufficient experience it should be entirely doable, but at least let it check by someone with some experience in this specific field.
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Mike Elliott
Film Handler
Posts: 3
From: Pittsburgh, PA, USA
Registered: Sep 2018
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posted 09-26-2018 05:08 AM
Marcel,
Thank you very much for the insightful response. Your comments seem to confirm most the research I had done which is a relief.
I had seen the HI/VI channels mentioned elsewhere but couldn't really come up with what their use-case was. The motion code makes a lot of sense. Is there any really pertinent information on these non-audio tracks that we should be aware of? Is there any auto-mixing that needs to take place? I would assume the mix is baked in, but I want to just confirm.
Again, the space is very "traditional". No rocking seats, no screen masking, etc. I have looked over the Atmos cinema specs and the PA is not even up to that level of spec. Nothing remotely fancy here.
I was not aware Q-Sys was making inroads into the cinema world. The Tesira Server I/O we are planning to use is a direct competitor (could argue QSC copied the Tesira). I find it odd though that QSC would push both their DCP line and Q-Sys for the same market.
As far as system tuning, that part I am confident I could handle. We have a SMAART rig with Earthworks measurement mics and very a low noise audio interface. However, to be safe, are there industry suggested tuning guides? I would assume the system should be tuned flat so as not to alter the mix, but again, I want to be sure.
The organization in charge of the films does want to bring out their own person for tuning at some point. However, more than likely I am going to need to do the initial pass. My goal though is for the tech to listen and go "sounds right, so why did you call me?" ![[Big Grin]](biggrin.gif)
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Harold Hallikainen
Jedi Master Film Handler
Posts: 906
From: Denver, CO, USA
Registered: Aug 2009
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posted 09-26-2018 05:21 PM
I like letting the Blu ray player do the decoding, either to analog or HDMI. It seems a waste to put decoders in every piece of equipment. The Blu ray player seems like a good location.
DCPs never use encoded audio. It is always linear PCM. There's a minor exception with Auro sound where additional channels are encoded in the least significant bits of existing channels (I don't remember if it's 5.1 or 7.1). But, this is compatible with existing 5.1 and 7.1, so no decoder is needed unless you need to run Auro. And then, the decoding happens in the Image Media Block before forensic marking is added.
The industry is moving from an ad hoc "standard" (Interop) for DCPs to SMPTE standard. There are a LOT of options in SMPTE, but ISDCF (see http://isdcf.com) is recommending use of one audio configuration with the audio channels in the same order they were for Interop (see http://isdcf.com/papers/ISDCF-Doc4-Audio-channel-recommendations.pdf ). If a server is configured for 1:1 routing (track 1 comes out AES 1, track 2 out AES 2, etc.). all should be well.
You mentioned HI/VI in a previous post. Current requirements for HI/VI and closed captioning are summarized at http://ftp.uslinc.com/ftp/MultiProduct/Accessibility/q_wp_cin_accessibilityrequirement_171129.pdf . You mentioned this was a theater in a school. That may or may not meet the definition of a movie theater for the purposes of closed captions and VI audio (now called audio description). I suspect, however, that the HI audio (assistive listening system) would apply. Something for your legal department!
Finally, on the QSC Q-Sys versus DCP series, I (and I work for QSC, but not on this equipment - I do work on the QSC acquired USL JSD series of equipment) see Q-Sys as a more advanced high end system with the DCP and JSD series being more traditional cinema sound processors. In any case, the sound processor provides audio input selection, audio routing, volume control, equalization, sync and surround delays, digital to analog conversion (if the power amplifiers have analog inputs) and an automation interface (now typically TCP commands over Ethernet) for the digital cinema server or other automation. The sound processor may also include crossovers for the speakers.
Good luck!
Harold
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Marcel Birgelen
Film God
Posts: 3357
From: Maastricht, Limburg, Netherlands
Registered: Feb 2012
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posted 09-26-2018 05:43 PM
Like with all technology, there are cases where people mess up stuff. There are some DCPs that ended up with matrix encoded sound in their channels. This is most definitely not what the DCP standard intended and most theaters aren't even set-up to deal with this.
If you're playing a lot of repertoire and independent titles, you'll end up with more badly produced DCPs than if you only play the first-run Hollywood content.
There are no reliable ways to detect any such misbehaving DCP, so you still need the knowledge of a tech or projectionist to handle this.
In case of matrix encoded channels ending up in DCP audio channels, you can use a CP650 or AP20 to work around this. There is a third-party virtual DSP plugin on the Q-Sys platform that can also matrix-decode tracks.
If you want to plan for those scenarios, you could still retain the CP650 you already have and use its matrix decoding functionality in such specific cases, where you feed the two digital channels into the CP650 and use the Format 80/81 functions of the decoder.
In many, if not most cases, those badly created 2.0 DCPs don't include a matrix-encoded soundtrack and they just copy the original mono track to the left and right stage channels. In this case, the best solution is to discard one of the two channels and route the other channel to the center channel.
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