Suround sound

[london sound]

I have been asked to supply a sound system for an outdoor cinema.

 

I can provide the speakers etc. however does anyone know how to get the source signal from a 35mm projector decoded into 5.1?

 

If so do you know of any providers of decoders (for hire) etc.?

 

 

Ian

[gareth]

I have been asked to supply a sound system for an outdoor cinema.

 

I can provide the speakers etc. however does anyone know how to get the source signal from a 35mm projector decoded into 5.1?

 

If so do you know of any providers of decoders (for hire) etc.?

 

 

Ian

You'd need a Dolby decoder of some sort (as you've probably realised!), but what kind depends on the projector and the print it's playing - i.e. digital or analogue soundtrack.

 

I don't know of any rental sources for such equipment - however, this document has a list of UK distributors for Dolby products, and one of them might be able to put you in touch with a rental company who carries this kind of kit.

[robloxley]

Where's the projector coming from - can they not help you out?

[James]

Dolby 5.1 is a domestic format.

 

you also need to find out what formats are provided on the print. Not all formats are on all prints, and normaly you have to be able to seemlessly switch between formats (ie if you are using dolby digital and the edge is dirty you need to switch to optical and decode into dolby stereo and seemlessly return when data is restored.)

 

Dolby stereo is the easiest surround format to use as you only need the stereo optical track, It's a L C R S system but requires the dolby decoding rack.

 

Interesting history of cinema sound formats.

 

Dolby CP45 Decoder (pdf)

Dolby CP65 Decoder (pdf)

 

James

[london sound]

Thanks, the above obviously tells me I need more info from the client.

 

 

 

Ian

[london sound]

Hi

 

Thanks for the help, this is the result.

1. The projector company recommend running the sound in mono!!

2. If we ran full surround Dolby would have to send their technicians and we would have to hire decoders from them!! (jobs for the boys)

 

 

So good old mono wins :D

 

 

 

Ian

[Bryson]

Try Future Projections: www.fproj.com who are South London based. They do outdoor projection, I understand. But they'll send you thier own techs too - it's not jobs for the boys, it's that setup of Dolby Surround sound is a specialist thing that has to be done properly.

[Big Dave]

Having just done a surround sound job last week, its actually very easy to set up as the processor has all the individual outputs on it. Its just a matter of balancing the levels correctly. The only complicated bit than I can think of would be setting up the processor but the one we used last week was literally plug and play.

[london sound]

Hi Dave

 

Could you please expand?

 

Like what processor?

Did Dolby have to come etc.?

 

 

Ian

[Big Dave]

The Video we were playing last week was coming from digital video source so it's not quite the same as film. The client brought their own M audio interface which gave us 10 channels (although we were only set up for 6) but it didn't require any adjusting on site. I just took 6 lines from the processor into FOH and routed appropriately.

 

However, I did quote on a film based job a few years ago and after a bit of digging, it was going to work out easier for us to buy the Dolby processor (about £2-3k I think). Because all the surround info was encoded onto the film, once you have the correct processer we were advised that it really was plug and play. Exact details are a bit sketchy as like I said this was a few years back and the job never actually happened in the end.

[IanG]

Is it the case that if you want the system to be officially Dolby certified (ie. allowed to display the logo and officially use the technology) then that's when Dolby want to get involved and the costs get prohibitive?

 

ISTR somebody telling me something along these lines, although it is a vague recollection.

[ljstevens]

Hi mate if the film is a dolby film it will have a magnetic strip down the right hand side looks abit like a bar code, if its sonys format then it will have a magnetic strip either side of the film, if its dts then it will have a solid magnetic strip down the right hand side! then youu will need the right sound head on the projector to pick up the relevent strip.

I know dts runs a seperate specialised cd unit which has 4 cd roms, these are timecoded to play from the magnetic strips on the film, this then outputs to your decoder! I think dolby and the sony format are based on the same principle!

 

so check the film you are playing to see if there is any strips running down the side, if there is a tiny magnetic strip on the right side then it means the film is in mono!

[James]

Hi mate if the film is a dolby film it will have a magnetic strip down the right hand side looks abit like a bar code, if its sonys format then it will have a magnetic strip either side of the film, if its dts then it will have a solid magnetic strip down the right hand side! then youu will need the right sound head on the projector to pick up the relevent strip.

I know dts runs a seperate specialised cd unit which has 4 cd roms, these are timecoded to play from the magnetic strips on the film, this then outputs to your decoder! I think dolby and the sony format are based on the same principle!

 

so check the film you are playing to see if there is any strips running down the side, if there is a tiny magnetic strip on the right side then it means the film is in mono!

Um Pardon.

 

Sorry but I have no idea what you are talking about.

 

I know of no modern commag film formats.

 

All the ones I know about DTS, DD, SDDS are variants of Commag using digitaly enoded timecode (DTS) or digital audio data (DD) printed directly on the film, No mag envolved at all.

 

http://kino.ricany.cz/obrazky/obr1.JPG

 

Here is a demonstration of the different optical film sound formats all on one bit of 35mm film together.

 

http://members.aol.com/cds3570/dcomp.jpg

 

In Between the sprocket holes on the left hand side of the film is the Dolby Digital Data. Each sprocket hole contains a 256x256 matrix of bits. At the centre of each square is a tiny version of the DD logo. When I was taught projectioning I was told that this was an important part of the encryption algorythm. (Ignore the section on the right the green bit is SDDS (See below) and the the right hand photo in gray is of CDS - another obsolite format)

 

On the right of that you can see two lines. This is the actual stereo analouge audio waveform represented as light. In the olden days this was a single (mono) line, now there is almost always two lines, the sum of which equals the mono equivelent.

 

On the right of the analouge audio is a single broken line of timecode. This drives the DTS system where the audio is read off a CD synchronised to this timecode. A very rugges system as the CD can free wheel if timecode is lost - something none of the other formats can do.

 

http://3dsound.zut.pl/film_sdds.jpg

 

On the outside of the film is a green strip on either side. this is the SDDS information. This is just digitaly coded audio printed directly onto the film.

 

Hope this helps

 

Just to repeat, None of this is magnetic. Whilst ComMag formats do exist they are archaic and I would shudder to see them anywhere outside of an archive, library or museum.

 

 

James

[Big Dave]

Some more info I have discovered this week. I was working in one of the theatres in the Barbican that has Dolby system installed and I got the house engineer to explain it.

 

The information James gives about the film is completely correct. Nearly all new films have all the popular audio formats printed on them. It then depends on which system the cinema has on what you get. Each different format has a different head to read the film as they all have slightly different offsets.

 

Also had a play with thir Dolby decoder. Its all menu driven from a nice clear LCD display on the from which allows you to select pretty much anything. Apparently, the only complicated thing about the set up is getting the EQ settings correct for the enviroment that you are in as you need to know the system. However, the engineer said that once it's been explained, any decent audio engineer could do it.

 

I took a pic of the system on my phone and I'll post it once I've downloaded it.