[LAD] Open Source Audio Interface

[Len Ovens]

On Thu, 11 Sep 2014, Paul Davis wrote:

> On Thu, Sep 11, 2014 at 5:44 AM, <karl at aspodata.se> wrote:
>
>       Why don't you prototype it with netcat:
> 
> 
> as powerful as some unix prototyping tools can be, just stop for a second.
> 
> although i'd be the first person to suspect stupid financial motivations
> behind the proliferation of audio-over-(ethernet|IP) solutions, do you
> really think that if delivery low latency audio streams was even remotely
> achievable with a tool like netcat that we would have seen the emergence of
> special network interfaces and completely new ethernet-level protocols?
> 
> audio-via-cat5 cable isn't a new problem, waiting for the right solution. it
> is an old problem with at least a half dozen solutions each with different
> pros and cons.

Not new at all. There are a lot of solutions. Many of them closed. AES3 
and AES10 are open standards. AES3 suffers from low channel count and 
aes10 suffers from expecive HW... and the need for an interface a laptop 
may not have. Laptops have become a desktop replacement for many people. 
(in a few years a smartphone may become a desktop replacement for some 
people too)

I think netcat is not needed for this project, It is still higher level 
than what would be the best use of ethernet. Raw ethernet at level2 (the 
MAC level) is the lowest standard level. But it is easy to use for 
prototyping. The main drawback for using a higher level (ease of use being 
the main plus), is that it assumes collisions and other delays and that it 
will work on a LAN where it will have to deal with other traffic. So it is 
easy, yes, but making it reliable is hard. It can be very reliable in a 
point to point configuration, but then the sw config tends to be less 
automated and not so easy for the end user. The other problem with high 
level network is the use of CPU and bandwidth for overhead. Netjack works 
well for me, I can set it up to be very good, but it does use much more 
CPU than a PCI or USB audio IF would use. I don't think there should be 
any reason for that in a point to point setup.

To rephrase, it will work on any LAN including one hooked up to the wire. 
Therefore it will get used that way and has to be able to deal with going 
through a switch that is dealing with downloading a movie in the living 
room and feeding a wireless AP. There will be complaints about it not 
working in those situations. Making it strickly P2P, level2 avoids all of 
that.

Latency is additive. This net transport is only a small part of the path 
and making it much lower than what is needed means that all the other 
things that add latency are still ok. So when I talk about link latency, I 
am talking about raw ethernet send to raw ethernet receive only at this 
point.



--
Len Ovens
www.ovenwerks.net