[linux-audio-dev] Audio synchronization, MIDI API

[Steve Harris]

On Sat, Aug 14, 2004 at 10:07:06PM +0200, Benno Senoner wrote:
> >UDP also has unbounded transit time. In practice its OK if you dont want
> >low latencies (just use RTP), but for low latency you really need one of
> >the non-IP ethernet protocols that can be relaibly used for audio.
> 
> I don't think raw ethernet will buy us anything over using UDP. These 
> few usecs less simply won't matter.
> (but with ethernet you would have the disadvantage that you loose 
> routability)
> On a 100Mbit network the round trip latency between hosts is about 
> 100usecs so the one way latency of MIDI would be
> about half of that. and that's form a MIDI point of view instantaneous 
> because over serial MIDI cable transmitting
> a NOTE ON event  (3 bytes) takes about 1.1msec which is 20 times slower 
> than transmitting it over an ethernet cable.

No, the roundtrip latency is *at least* 100usecs (or whatever), the hardware
will keep re-transmitting until the packets get through.

In pratice people dont really demand hard realtime and it will be OK, but
the maximum time taken to transmit a UDP packet is unbounded, it uses
exponential backoff IIRC. 

This is why latency sensitive application have used token ring networks
traditionally.

- Steve