Re: [chuck-users] syncing computers with OSC

One more thing -- do be wary of UDP, it *does* drop packets sometimes. TCP is pretty flaky with reception delays, though. I even tried writing some custom socket code and found some really weird timing issues that I think were related to internal Apple network device driver buffering. brad http://music.columbia.edu/~brad On Jan 28, 2009, at 9:11 PM, Brad Garton wrote:

Yeah, I don't think IP was set up for "sample accuracy". Maybe on an I2 network. I guess one possibility would be to transmit an audio signal and design some kind of phase-locking system that would keep sync, but delays might(!) creep into such a system without detection. I recall Chris Chafe telling me about a really snazzy thing they had done at Stanford where they used the delay inherent in IP transmissions as a delay-line for a phys model like the Karplus-Strong algorithm; they would periodically 'pluck' the delay line and the shift in pitch would signal how much latency was being introduced (I think this was intended for remote operations where knowing the delay was important).

In my pLOrk piece, I sent a 'sync' pulse about every 0.5 seconds from one machine, and all others would reset their clocks to correspond with this. It worked fairly well, although 'sample-accuracy' is in the ear of the beholder, I suppose.

Another technique is to have the performers actually look at each other...

brad http://music.columbia.edu/~brad

On Jan 28, 2009, at 3:59 PM, mike clemow wrote:

...

We looked into doing this while running Chucks on a cluster here at NYU and realized that for things like sample-accuracy (or sub-sample-accuracy, god forbid) even NASA has significant problems. I think that some sort of hardware system (cesium clock or something) is necessary for that. Obviously, that's outside of everyone's budget. ;-)

But syncing tightly enough for musical performance should be totally possible.

-Mike

On Tue, Jan 27, 2009 at 10:22 PM, dan trueman wrote:

...

well, we actually do a lot of synchronization over the network, and it works amazingly well (with UDP). it's nowhere near sample accurate, but it's musically powerfully accurate, and it's important to keep in mind that "accuracy" in something like plork is not easy to define, since all the sound sources (multichannel hemispheres) are spatially separate and there is a lot going on with phase -- the speed of sound becomes a major factor! if you are mixing multiple computers with a mixer, then i can well imagine that network sync will be insufficient, but when the room is doing the mixing, it is almost overly accurate; it feels un-natural how well a large ensemble can sync this way (and it is!). dt

On Jan 27, 2009, at 7:39 PM, kevin wrote:

nobody in plork or slork is synced, which is, in my opinion, one of its stronger points. the music sounds more attached to the performers and less attached to a computer, if that makes any sense.

intra-computer sample-accurate syncing over a network is difficult because neither TCP nor UDP are suited to such things. TCP guarantees packet delivery by requiring a call-back (sometimes called a handshake). if the sender does not receive a call back, it assumes that the packet was dropped and then resends info. this works for things like websites, where the request is not time-sensitive.

UDP on the other hand, does NOT guarantee packet delivery, and thus expects no call back. when packets get dropped over UDP, the sender is not notified, so the sender will not resend. this is better in situations like VoIP, where a single dropped packet will not ruin the audio stream (sure, there'll be a noticeable glitch). the idea is that if you're talking to someone, you'd rather hear a glitch than hear that packet arrive 5 seconds later.

without modification, neither are sufficient for real-time synchronization.

and even if they are, wifi bandwidth will definitely get in your way. i haven't looked at any numbers, but i'd intuitively guess that wifi drops more packets than wired.

On Tue, Jan 27, 2009 at 4:15 PM, wrote:

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I see. so none of the Plork pieces are dependant on precise synchronization? I guess because I am coming from a dance music background its more critical for me that the music is running off a master clock. I was thinking that Chucks strongly timed quirkiness would enable me to send sample accurate osc messages albeit at a very high speed cost. I suppose I can try midi but was hoping for a wifi solution.

Quoting dan trueman :

...

i don't think there is any way to get sample-accurate sync via conventional networking...

dt

On Jan 27, 2009, at 6:51 PM, james.hurlbut@utoronto.ca wrote:

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Hi, chuck newbie here. I am wondering what the best way to get sample accurate sync between two laptops. I have tried using http://music.princeton.edu/~dan/plork/autosocket_chuck.zip but the two computers receive the 16th beats at slightly off times. I also have tried sending an osc message every sample or 100 samples but that completely bogs down the machine. Is the solution to have one machine do all the audio and another just send program changes? Thanks,

James

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