[LAU] FOSS Ethernet Soundcard

Karl Hammar karl at aspodata.se
Tue Nov 24 05:08:19 EST 2009

> >> Recent discussion on LAU morphed into an idea for an Ethernet
> >> driven sound card, and as this is now becoming a real
> >> development 
> So I will plug this into my ethernet and have < 1ms latency? :)

The "this" part is currently only in our minds for the moment, but if 
you solve the issue of connecting our "minds" to your ethernet port, 
I'll solve the 1ms latency part :)

A simple ping:

  $ ping granat
  PING granat.lcl.aspodata.se ( 56(84) bytes of data.
  64 bytes from granat.lcl.aspodata.se ( icmp_seq=1 ttl=15 time=0.758 ms

gives me a round trip of < 1ms, so it should be possible.

So the time from analog, pushing out samples from the sender port,
till it is received the receiver port would be lower bounded by:

 sample conversion time
 lcl transport time to cpu
 cpu processing
 cpu to ethernet tranceiver
 ethernet preamble (assume quiet net)
 cable delay
 packet bit speed * packet length

Add to this any processing on the receiving side.

To help achieve low (network) latency one can:

. set up fixed arp entries (see arp(8))
. use fixed ip-addresses, no dhcp, no mDNS, no autoconfiguration or 
  other talky protocols
. don't mix other hosts on the lan, make it as quiet as possible
. no DNS, use /ets/hosts files
. if possible use a crossover cable [1]

What kind of latency do you think would be a goal to strive to ?


[1] http://en.wikipedia.org/wiki/Ethernet_crossover_cable

Karl Hammar                    Aspö Data               karl at aspodata.se
Lilla Aspö 148                                                 Networks
S-742 94 Östhammar          +46  173 140 57                   Computers
Sweden                     +46  70 511 97 84                 Consulting

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