Re: [LAU] open hw soundcard

On Sat, 14 Nov 2009 09:34:15 -0500
Paul Davis <paul@email-addr-hidden> wrote:

> On Sat, Nov 14, 2009 at 8:04 AM, Karl Hammar <karl@email-addr-hidden> wrote:
>
> > So what is the consensus among the applications, is it e.g. "/mixer/1/
> > volume", "/mixer/a/vol", or what?
>
> To the best of my knowledge, there is no consensus about the format of
> any significant messages sent via OSC. There is no standard way to
> generate specific behaviour in an unknown OSC receiver, whether it is
> volume control, note generation, or anything else. All the uses of OSC
> that I am aware of involve a set of messages specified by the sender
> (in the case of, say, the Lemur or Monome control surfaces, or the
> Mrmr iPhone app) or by the receiver (in the case of, say, Ardour or
> Reaktor).

Well it's been wet and windy all day today, so instead of going out I
did some more reading :)

With this lack of standardisation is there any point in going for OSC
with it's quite significant overhead? Netjack also seems to have quite
a high overhead, and no specific mechanism for RT syncing audio.

It seems that the UDP protocol is already the preferred protocol for a
number of streaming media apps (1) for the same reasons as I mooted
earlier. Low packet overhead, virtually any packet size, chuck it out
as fast as the transport layer can cope with.

Maximum packet size for Ethernet is 1500 bytes, but I suggest we really
don't want to get anywhere near that big if we are to keep latency
down. Off the top of my head, a 'full' frame would hold about 15mS of 1
channel 48kHz 16bit.

The downside is no congestion control, so if the network gets congested
you will lose packets rather than have them stack up in a (probably
high latency) buffer.

With just one card talking to the computer I don't think packet loss is
a significant problem.

With enough bandwidth, I would suggest a simple round-robin system
whereby every slave listens continously, but only sends when told to by
the master.

On the hardware side, that Atmel development kit (2) looks very
interesting as a proving ground as it already has both the network and
the 48kHz DAC parts built in.

For rough testing it could be used to lock a pair of ADCs. TLC4545ID
looks like a good (cheap) possibility here.

(1)
http://www-net.cs.umass.edu/kurose/transport/UDP.html
(2)
http://www.atmel.com/dyn/products/tools_card.asp?tool_id=4102

-- 
Will J Godfrey
http://www.musically.me.uk
Say you have a poem and I have a tune.
Exchange them and we can both have a poem, a tune, and a song.
_______________________________________________
Linux-audio-user mailing list
Linux-audio-user@email-addr-hidden
http://lists.linuxaudio.org/mailman/listinfo/linux-audio-user