Sun, May 16, 2010  

Dave: "Milliseconds count. While you might be able to patch together a homegrown solution using your existing sound card and some type of VoIP or voice chat app, you will have a difficult time reducing the latency created by all of these combined components, as well as the Internet travel time, to meet the 25-30ms one-way delay requirements for real-time, synchronized playing.

"The jamLink is designed to add the minimum possible delay to the total one-way delay budget in a session between two or more musicians. In a jamLink session, the majority of the actual latency is introduced by the Internet travel time, not the jamLinks at the endpoints. Considering that average Internet delays across regional distances are relatively low, players in jamLink sessions can achieve one-way delays low enough to feel as if they are playing in the same room as their collaborators.

"Additionally, the jamLink simplifies the session setup process for all of the users in a jam. Connecting to the other players is like starting a Skype call or chat session. And since the audio is fully uncompressed, there is no loss of quality or additional delay added as a result of the compression."

Theoretically, sending data over the Internet can't be done without latency. Even with a fiber optic point to point connection, there's always the speed of light as a limitation while switches and routers on the way form another constraint. What would be the theoretical maximum distance for musicians to jam over the web? Sydney, New York, Moskow - would that be a realistic setting?

Chris: "You're correct - these are the two sources of delay: distance and routing gear. The answer to "how far can we go?" depends on these and on the type of music. Different kinds of musical interaction tolerate delay better than others. Some rough limits: for tight, fast rhythmic coupling you want your one-way delay to be under 25-30ms. That's where the 500 mile number over commodity Internet comes from. For say, someone performing a tempo knob on a drum loop while playing with a full band, it's quite different. No numbers for that, but my experience has been it's way longer and probably, yes, Moscow playing with New York. Last year, we performed a concert with Seoul, San Diego, Belfast, Banff and NYC with 25 musicians playing music that was more solo/ambient in nature."

One needs to login to MusicianLink to be able to use jamLink. Is there some kind of central nerve system running at MusicianLink, monitoring all latencies - or is it just a matter of validation and establishing the initial connection(s) between musicians you'd like to jam with?

Chris: "At present, the "backend" is for the latter, maintaining a presence list and dishing out initial information need to initiate connections. We have an app under development that monitors fine-grained latency information. Not a "speed test" but one that checks all aspects of QoS relevant to Internet audio transmission. Users will learn delay from it."

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