[LAD] Open Source Audio Interface

Len Ovens len at ovenwerks.net
Thu Sep 11 22:50:31 UTC 2014

On Fri, 12 Sep 2014, Arnold Krille wrote:

> On Thu, 11 Sep 2014 14:24:56 -0700 (PDT) Len Ovens <len at ovenwerks.net>
> wrote:
>> Where I see your info as being useful though, is if I choose to send
>> data (which could be varying sized packets) I may still wish to set
>> the data packet size to a fixed size depending on what is left from
>> audio. The whole network end of things needs to be decoupled from
>> real time.
> That last sentence is a bit contradicting. You want to send audio over
> network, you want the audio to be near realtime. But you want to
> decouple network from realtime... (In math: A==B && B==C && A!=C)

Shouldn't be, The network traffic does not need to be real time, but the 
network does. In other words the way the host computer deals with network 
traffic does not need to be real time. The computer puts a packet into a 
buffer, this part does not need to be real time. The network sends it 
while there is no audio traffic, this part does need to be real time.

>> To be honest, I have spent a lot less time thinking about the network
>> traffic part of things than the audio part of things. The reason for
>> this is that the use cases for allowing network through our line is
>> small. As has already been commented, a desktop can have a second NIC
>> and the laptop generally has wireless. The main usecase for network
>> through the same IF might be radio work where one might have a SIP
>> connection (phone line) going through net. (anyone see others?)
>> Because the AI has a second NIC and an OS, it should be possible to
>> set up the SIP session on that box.
> There is a widespread use-case for audio and non-audio network traffic
> on the same segment: audio and control/midi messages on the same
> segment. And you don't want your fader moves to interrupt your audio.

Yes. I have included midi links in real time as it happens as part of the 
audio packet. network data has other uses and that was why I wanted both.

> And your current thinking seems to be about using a dedicated
> network-link between PC and audio-interface with a possible chain-link
> to other interfaces. But what about a dedicated network (with switch)
> to connect multiple PCs and audio-interfaces? Then you have to deal
> with lots more channels, thus lots more realtime data and also lots
> more control-messages.

Why? there is already stuff out there that does that (with higher latency 
of course) The main idea is still to replace a FW audio interface up to 
around 32 channels, not provide a generic network audio protocol.

> PS: Maybe this question sound foolish: Why not AVB / open AVB?

What is the latency? Or what is the minimum latency I could get on a link 
with say 50% audio/network traffic and a 100m link? The real show stopper 
though is that the end points require dedicated HW. That is it would not 
just work with the average laptop or desktop NIC. AT least with the 
desktop a new NIC could be added. The question as to the NIC driver 
actually using the required capability is something else.

Len Ovens

More information about the Linux-audio-dev mailing list