[linux-audio-dev] Re: Language fanboys [was Re: light C++ set for WAV]

[lazzaro]

On Jul 23, 2006, at 2:06 PM, Dave Robillard  
<drobilla at connect.carleton.ca> wrote:

> I don't see it as much of a problem anyway.  At least in all my use
> cases, there's realtime crucial data (eg what MIDI tends to do,
> controllers, notes, etc) and there's data that just needs to get there
> sanely.  The nice thing about the realtime stuff is that lost messages
> don't really matter, all you care about is the most recent one anyway.


Well, consider a volume slider on a mixing console.

One way to send its state is to sample its value and
send a packet every millisecond.  In this case, your
"nice thing" is true -- the occasional burst of lost
or reordered packets will only cause brief "transient"
artifacts.  The price paid for this "nice thing" is
sending 1000 packets per second, every second
of the performance.

The more efficient way to send the slide state
is to only send packets when a human finger
moves the slider.  In this case, your "nice thing"
is not true -- the slider might be moved by the
human once per minute, and if the packet coding
that move is lost, that lost packet matters for the
entire minute.

RTP MIDI's recovery journal lets you safely use
this incremental update approach over a lossy
packet stream in an efficient way ... if
you need to send data over lossy networks
and that fits MIDI's semantics, and TCP's
head-of-line blocking latency is not acceptable,
I think RTP MIDI is the right protocol to use.

---
John Lazzaro
http://www.cs.berkeley.edu/~lazzaro
lazzaro [at] cs [dot] berkeley [dot] edu
---