Portable synchronized mutli-channel playback

lifeofbirds · Post by **lifeofbirds** » Sat Oct 27, 2012 10:26 am

Hello all,

I am working on a project where I need to synchronize playback on 30 (pre-recorded) unique audio tracks that can be heard by 30 discreet performers.

I actually did this a few years ago using ipod nanos and a third party remote system called ijet -

http://www.buyijet.com/top-products/ije ... emote.html

I purchased 30 of these ijets and connected them to 30 ipod nanos and synched all the ijets to one remote. When I hit play all 30 nanos would start at the same time. The problem was, that they didn't start at exactly the same time (probably about a 500ms lag between them) AND sometimes one or two wouldn't trigger and then I would have to manually stop them all, and try to synch again...it was pretty hit and miss.

I no longer have the ipod nanos - they were kept by the institution that originally funded the project. And now I am gearing up to do the performance again and I want to figure out a better way to sync start a multi-channel system like this.

One option would be to purchase these mp3 triggers which can start a track by pulling a pin low...

https://www.sparkfun.com/products/11029

So I could purchase 30 triggers (and build casings, buy batteries, etc.) and have them all terminating to one pin which could switch low and simul-start all of them at once. I can test these for lagtime, and so far these are seeming like the most obvious solution.

An entirely different route I was thinking about would be 30 wireless in ear monitors, receiving audio from a multichannel DAC, but the costs of that would be astronomical.

Or I could use 30 fm transmitters (and 30 radios for each peformer) - I don't know a lot about this, but I am guessing that legality, interference/stability , and cost would be issues.

Or maybe use wifi somehow?

Wireless could be really great because then I could make changes to the tracks and not have to reload all the mp3 players. And I am planning on making a lot of changes over the course of the project.

I know this is a lot, but I would really appreciate any ideas/suggestions.

kslight · Post by **kslight** » Sat Oct 27, 2012 11:02 am

Maybe I'm missing something about your project, I'm not exactly clear on why you'd need 30 individual units (or if you do?). Is it just that they have be monitored by each individual on headphones..? Do they have to be mp3 players?

Also not clear if you are talking about 30 stereo audio tracks, or if they can be mono.

Not sure of your budget and practical requirements, but you could maybe rent a few multitrack hard disk recorders (or ADATS, HAHA!) like the Alesis HD24, Tascam x48, Mackie, etc....sync them all together and use a remote. Run that into 30 different headphone boxes. Maybe not the cheapest but I'm betting it'd be more rock-solid than syncing up a bunch of consumer devices.

lifeofbirds · Post by **lifeofbirds** » Sat Oct 27, 2012 1:40 pm

Sorry - I guess it could've been clearer. I want 30 independent mono tracks that can be heard by 30 independent performers. Each performer will listen through headphones to a portable device (mp3 player, wireless in ear monitor or..???). And the clincher is that I want all 30 tracks to start simultaneously so that they are in sync.

kslight · Post by **kslight** » Sat Oct 27, 2012 2:12 pm

Sorry - I guess it could've been clearer. I want 30 independent mono tracks that can be heard by 30 independent performers. Each performer will listen through headphones to a portable device (mp3 player, wireless in ear monitor or..???). And the clincher is that I want all 30 tracks to start simultaneously so that they are in sync.

So correct me if I'm wrong, but the solution I proposed then would work very well for your purposes? That to me seems like the most straight forward way to have everything playing in sync, hitting play on a multitrack device and running each output into a headphone box? I think the cost would be no more than say...30 iPods...and the sync would be perfect.

The Scum · Post by **The Scum** » Sat Oct 27, 2012 2:35 pm

Conventional Wireless in-ear systems might be problematic for a couple reasons.

I'm having trouble getting a hard number from Shure's website, but I don't think most hardware supports 30 channels (Shure's hi-end bodypacks say they can scan 20 channels...Sennheiser's say 16...though some of the transmitters are claiming 20 banks of 32 bands...however that really works out).

Also, depending on what you have to share the spectrum with, you might not actually have all of the bands to work with - you'll be sharing spectrum with other users, and have to find bands that aren't already in use. There's no guarantee that there will be 30 bands free.

Granted, I haven't done anything with wireless since before the HDTV changeover. The rules and spectrum are all different than what I know, and I'm just judging based on the datasheets.

But you say it's mono - so you could conceivably use stereo units, wired for mono, to double the number of discrete audio channels available - assuming inter-channel crosstalk isn't too significant.

Those MP3 boards from Sparky are also an order of magnitude less expensive than a mid-grade in-ear setup.

lifeofbirds · Post by **lifeofbirds** » Sat Oct 27, 2012 2:59 pm

The hard disc recorders would work great except for that I want the performers to be able to be "wireless". I wouldn't want them tethered to anything - that's why I was thinking mp3 players or wireless in ear.

As for the wireless...I think you are right in that the main issue would be interference. But good idea on the stereo split to double the number of channels. It seems to me that for stability and price the sparkfun mp3 players might be the way to go. Unfortunately they suck power down pretty quick - a rechargeable 9 volt only lasts about 3 hours, and a bunch of AAs will make them really bulky. And then I'll have to make some housings for them as well. Wish I could just hack a sans clip to trigger simultaneous playback, but that is beyond my skills.

Thanks for all the feedback!

Nate Dort · Post by **Nate Dort** » Sat Oct 27, 2012 3:31 pm

The easiest way to do this is to set up a giant induction loop around the performance area and hand out a bunch of IEMs to everybody. Discussion here: http://jwsoundgroup.net/index.php?/topi ... -neckloop/

You should be able to rent everything you need for this.

Snarl 12/8 · Post by **Snarl 12/8** » Sat Oct 27, 2012 3:52 pm

I used to use LTSP (Linux Terminal Server Project) for thin clients in my house. It didn't work so well over wireless or with video, but audio support kept getting better and better and you can get teeny, tiny mobos that support it for peanuts these days. You could use any sort of computer for the server. The DAC's would be on the mobos and you'd stay all digital until then using regular old wifi. Might be worth a look although the configuration might take a while to suss out.

http://www.ltsp.org/

Something like this for the clients...
http://www.raspberrypi.org/

I just had a thought. You can configure Linux for telephony using something like Asterix. (IIRC) What if you had a server that called up all the performers' cell phones and played back tracks off of something like Ardour for the back end. You might not need to buy a single thing, except maybe an Asterix guru's time. Leverage the cell network.

There should be an app for this.

Gregg Juke · Post by **Gregg Juke** » Sat Oct 27, 2012 5:16 pm

I wonder if Korg has any software/apps for iPod that play Mp3's? I know that the Kaossilator 2 (hardware version) can, but what about the app? If so, you might be able to use Korg's WIST app to synch everything.

BTW, I don't work for Korg, it's just an intriguing, and possibly elegant, solution.

GJ

chris harris · Post by **chris harris** » Mon Oct 29, 2012 7:28 am

Even if you can get the start to synchronize on 30 different ipods simultaneously, you will not maintain sync throughout the duration of the song. There will be drift.

See: Zaireeka

lifeofbirds · Post by **lifeofbirds** » Mon Oct 29, 2012 7:32 am

Really? I assumed that because the mp3s are digital that a simultaneous start would mean that they wouldn't drift apart. Would they somehow process the information differently and so playback at slightly different speeds?

LTSP and telephony are very creative solutions. Thanks for the recommends - I will try and do some more research on those to see what I can turn up.

And the Korg Wist is really intriguing as well.

I'll let you know what I find and may be back for some follow up questions.

Thanks again.

Dakota · Post by **Dakota** » Fri Nov 02, 2012 10:22 pm

lifeofbirds wrote:Really? I assumed that because the mp3s are digital that a simultaneous start would mean that they wouldn't drift apart. Would they somehow process the information differently and so playback at slightly different speeds?

The files may be digital, and if all played back using the same reference digital timing clock, would stay in synch. But on a whole bunch of separate playback devices, each device having a separate clock circuit that's good enough for consumer mp3 playback but is not mil-spec or science spec... no, they will definitely drift in a way that would be obvious across minutes.

The above idea of leveraging cell phones - very intriguing! but I would not want to trust that 30 calls in one tight area would not have the closest towers dropping some of those calls.

Inductor loop totally not workable here - there are 30 distinct separate feeds, inductor does one feed.

The only bulletproof and cheap way I can picture this working: a single multitrack file playing from a DAW, each of the 30 guide tracks assigned to an individual output each, those out to headphone distributor amps, & cheap headphones for 30+.

If I had to spec this fast and cheap off the top of my head:
* A reliable laptop or tower computer. Need not be fancy, playing 30 tracks with no fx is easy even for old computers
* Installed multitrack DAW software - Reaper is cheap and solid
* 32 channels of interface, say 4 behringer ada-8000's or whatever bang-for-buck equivalent
* 32 channels of headphone amp (30 performers plus monitors for you too!) - ART headphone amps or aphex or rane or behringer or whatever you get a deal on that work tolerably
* 31 headphones - these could be buds or over-ears, look into "studio pack" lots

You can cut costs by using 16 headphone amps and splitting the left and right of each out, as your source files that need to get to the performers are mono. You'd need to custom wire some splitter cabling for that.

I know you wanted wireless... 30 reliable wireless channels is some serious $ and tech.

Is this a long poly-rhythm thing?

Gregg Juke · Post by **Gregg Juke** » Fri Nov 02, 2012 10:32 pm

Dad-gum, Dakota, but that was a solid piece of thorough analysis! If I ever need 30 independent playbacks of single, synching tracks, with appropriate monitoring in a performance application... Well, you're the Man, 50 Grand, anyway...

GJ

Dakota · Post by **Dakota** » Fri Nov 02, 2012 10:35 pm

Now if this were at MIT, it would be a whole different thing - they'd rig 30 infra-red transmission lasers, each with distinct amplitude modulation or a digital coding scheme, and rig 30 portable optical-to-audio pickup rigs to headphones. Just for the fun of it.

Dakota · Post by **Dakota** » Fri Nov 02, 2012 10:39 pm

Gregg Juke wrote:Dad-gum, Dakota, but that was a solid piece of thorough analysis! If I ever need 30 independent playbacks of single, synching tracks, with appropriate monitoring in a performance application... Well, you're the Man, 50 Grand, anyway...

GJ

I'd be surprised if that couldn't be done for under 5k, if you spec'd everything just enough to get the job done...

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Portable synchronized mutli-channel playback

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