Well, at one level is a philosophical issue. Ethernet mandates a computer, albeit a smaller one than what you use, but nevertheless a computer that is running a ton of code and creating events that occur in audio band (e.g. a timer that ticks to keep time). While anything can be quieted at some expense, physical size and effort, all else being equal you want that outside of the DAC. Digital interfaces like USB, S/PDIF, etc. can be implemented with far simpler processing units.
The other issue is support and reliability. Anything to do with networking brings in boatload of support issues. Yesterday my NAS just decided to show half the songs in one of my albums. I had to reboot it to see the rest. I knew that but others may just point the finger at the DAC. And proceed to call the DAC company demanding that they fix this problem because that is where the problem manifests itself.
The DAC company also needs to build up expertise in supporting computer systems inside their DAC. Yes, they can buy a module to use but still requires work on their part.
So lots of barriers against the convenience of having that connectivity. I suspect over time more and more DAC companies to support networking out of market necessity.
IMHO, an "Ethernet input" means a built-in streamer. And a streamer is so much more than a mere "input". It's not like adding an SPDIF or even a USB port. A streamer is a much more complex beast, with *gasp* software built-in.
In the end, the companies that invest, that do the legwork, and not merely slap a third-party streamer "thing" inside a DAC, will always have the best products, either in terms of sound quality and/or reliability.
Linn has invested millions in software for its products, and it clearly shows, as their stuff just works.
Soon enough there'll be "streamer boards", so every DAC will come with a built-in streamer, with little incremental cost.
As others pointed out, the networked DAC is simply a tiny computer with a sound card.
All streamers are networked computers by design.
They have become popular because there is a standard (UPnP/DLNA) allowing products from different manufacturers to communicate with each other (UPnP=Universal Plug and Play, indeed a pun on Microsoft’s PnP).
Today DLNA works reasonably reliable.
There are DACs with an Ethernet input working the way like SPDIF does, using a direct low latency protocol like AVB, Cobranet, Dante, Ethersound, Ravenna, etc.
Obvious there is no standard.
Likewise you can’ plug them in in your PC without installing some software.
Maybe AES67 will standardize the lot a bit.
I do think this to be an interesting solution because Ethernet
- No severe limitation in length like USB
- Galvanic isolated by design
Products using these protocols are targeting the prosumer market.
The only consumer version I know is: http://nadac.merging.com/
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