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This topic comprises 3 pages: 1 2 3
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Author
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Topic: Drive-In Wifi Sound?
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Barry Floyd
Phenomenal Film Handler
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Posts: 1079
From: Lebanon, Tennessee, USA
Registered: Mar 2000
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posted 02-22-2019 11:02 AM
I've never seen that system before, so I can't really tell you anything about it.
I know Sennheiser makes a similar system called Cinema Connect. It does both audio and descriptive text for hearing impaired. I called once about the Sennheiser system, and was told it was not available to the US Cinema market... which I think was a load of BS. I was the perfect system to use in a drive-in setting.
One thing I've heard from others about trying to develop such a system as "streaming audio" for drive-ins was "Latency". The more customers connected to the system, the worse the latency issue became.
I would be curious as to what something like this system costs and how well it performs.
Our customers ask us constantly for wifi streaming of audio, so hopefully this system might work out IF the costs are reasonable.
EDIT: After looking over the system on-line, I called them and spoke with "Brian". He said they have sold several systems in the last week to 4 other drive-ins, the SACO in Maine, the Black River in New York State, and the Starlite in Wichita. I'd probably wait a couple of weeks and call up some of these other drive-in owners and see how it works.
For the price, it's really not that expensive. I've wasted a whole lot more money on stupid stuff over the years than what this system costs.
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Marcel Birgelen
Film God
Posts: 3357
From: Maastricht, Limburg, Netherlands
Registered: Feb 2012
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posted 02-22-2019 11:45 AM
The advantage could be that you can support multi-channel audio and the digital signal could boost the quality. In practice, it's not that simple.
Latency will not be your friend, there is a lot of stuff involved that will make it difficult to get the latency correct for all things involved:
- Wifi itself incurs latency, also there is a considerable challenge to get good in-car quality all over the field and also to serve all clients simultaneously. - If you serve everybody with a unicast stream, even bandwidth can become a potential problem. Broadcast over wifi isn't all that reliable too. - Encoding and streaming will introduce latency, although this part is the part that's the most easy to compensate for, since it can quite easily be measured. Also, by creating a "fake buffer", any large jitter in the system can be compensated. - Your mobile phone will introduce latency in the networking stack, the decoding/processing stack and then also in the playback stack. - You probably don't want to play it on the wacky speakers of your mobile phone, so you connect it to Bluetooth... e.g. that of the in-car Bluetooth system. This will not only incur the latency of the phone, Bluetooth itself, but also that of the car Bluetooth and stereo system.
With so many layers of unknown in between, lipsync audio will become an afterthought.
For subtitling, it will work, but subtitles are far more graceful than audio.
And besides all earlier mentioned arguments: Don't forget the extra level of customer support for telephones not working, car Bluetooth systems not pairing with the phone, people forgetting to connect to the correct Wifi network, phones not connecting to the correct wifi network, outdated phones, phones with issues, etc. etc...
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Dustin Grush
Film Handler
Posts: 14
From: Johnstown, PA, USA
Registered: Apr 2018
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posted 02-22-2019 02:52 PM
Carsten, We do have a few radios that we hand out, free of charge, with a drivers license as collateral. This has worked rather well over the past few years that we have done it, and I have yet to have one go missing. At one point I even had out local screen print shop look into getting personalized ones with our logo, but the minimum order was ridiculous.
Monte, Up until now that has been my answer as well. Of course I occasionally get the "well it works at so-and-so drive-in..." Its even funnier when they tell me that it works at our other location, not realizing that the two are under the same ownership, just with a different name.
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Carsten Kurz
Film God
Posts: 4340
From: Cologne, NRW, Germany
Registered: Aug 2009
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posted 02-22-2019 05:34 PM
When you trace the equipment used through Google, you'll see that they use dedicated Wifi-Access points that specifically enable simultaneous streaming to many users. The manufacturer also has technotes on typical latencies down to individual typical smartphone processing latencies (typically, half as long on iPhones compared to typical Android devices).
Now, for a drive in, you would certainly need to support both FM radio and Wifi simultaneously, with both needing specific audio delays. It can be done, if you set your server to output audio earlier than video, then feed the audio towards the FM transmitter through a PA delay line set to the typical overall Wifi system latency, and a non-delayed version towards the Wifi system. So, the audio comes out of the server too early, the Wifi system latency brings it back in sync, and the additional delay line for the fm transmission 'simulates' the WiFi latency over the fm, so both FM and Wifi audio arrive at approximately the same time.
At first, it is probably not a big deal to start such a system, as only few people will be using it simultaneously. The question ist, will it really be trouble-free if a higher number of users hook up to it. Will there ever be a significant number of Wifi users?
Also, if people ask for it, you need to direct them to a dedicated app. No big deal, you can show a slide during preshow, with the app name, a QR-code, etc.
They will need to be able to download this app on site. Hard so say wether they will be prepared or able to download this through their 3G/4G (...) network connection (coverage?), or through your Wifi. In the latter case, your audio Wifi will also need to supply an internet connection. Their audio server also allows to supply internet, so, techwise, that is possible, if your site has internet connectivity.
Patrons request for Wifi may also be generic, as I suppose many patrons would love to use a free Wifi on your site before or during the screening. But that's a different service.
One potential issue is that smartphones usually stick to either 3G/4G OR Wifi, but not both. If they connect to your audio Wifi, and that Wifi offers no internet connection, attempts to download the app will fail, as that Wifi is a dead end. Patrons would need to switch back and forth between different connection types in order to download the app, and then to receive audio. Then when they receive audio, they will be offline, and wonder why...
So, all in all, there are many reasons why you should expect complaints or requests for help. Are you prepared to deal with all these smartphones your patrons will probably stick out towards you?
- Carsten
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Carsten Kurz
Film God
Posts: 4340
From: Cologne, NRW, Germany
Registered: Aug 2009
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posted 02-28-2019 05:16 AM
Another comment towards possible latency issues:
This document from one of these Wifi-live sound companies suggests typical device specific streaming audio latencies for Android and iOS devices being in the 170-460 ms range.
https://www.listentech.com/wp-content/uploads/2017/05/LTN0012_Wifi-Latency-Tech-Note_042717.pdf
The document is not precise as to wether the given values are 'device-only', or, full system (audio-input of encoding server - > mobile device headphone output).
Whatever - in order to compensate for this delay/latency, the cinema server has to advance the audio against the video during playout so that it will arrive at the client in sync time.
A Doremi has an adjustment range of -200 (earlier) to +200ms (later). I know other servers to allow e.g. -250ms to +250ms. For HD-SDI systems, the image processing will usually introduce a delay of 2-4 frames (no idea for IMB/IMS) for the video anyway, so, for a Doremi, the maximum effective Wifi latency correction ('predelay') possible is in the 250-280ms range (audio adjustment range plus inherent image delay). So, if those figures in the above document are correct and depict full system latency, it may just work decently for typical iOS devices. If a patron experiences an audio delay in the range of 200-250ms, that is certainly not tolerable, especially if the user uses e.g. a bluetooth connection into his car audio system which introduces another delay in the 50-100ms range (which is typical number).
If typical latencies experienced in the field, as depicted in that document, really vary between 170ms and 460ms (and I expect even more variations under non-optimal reception, heavy load, etc.), that range alone is unacceptable because you can only compensate for an average fixed delay, not for every individual user. But if one or multiple patrons experience a sync error of e.g. 200-300ms, that is unacceptable.
I'm not saying it wouldn't be possible, but, these are questions that a company offering these systems for 'cinema' use must be able to answer. They also need to be able to explain dual system aspects (as parallel FM/Wifi use with their specific delay needs).
- Carsten
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