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In Reply to: RE: Excellent post! Thank you and one quibble. posted by John Swenson on October 24, 2009 at 22:57:35
John, you have go slow with me -- I'm just a dumb analog guy.
I'm not sure what you're proposing here. It sounds like you want to install a complex computer as a server and then put a simple computer as a receiver.
Enabling the complex music server to use any music player software will require something called JACK that will let the software talk to the Ethernet port. Then the simple player only needs a $10 FPGA with a $9000 software core to decode the Ethernet.
So far, it sounds a lot more complex than USB. With USB, the drivers in the server are in the OS already. Then the receiver only needs a $3 USB chip (and a licensing fee to Wavelength, or program it yourself).
The bit advantages of Ethernet are longer cable runs (1000' versus 15') and built-in galvanic isolation with the Ethernet transformer. We have to add about $20 worth of opto-isolators the way we do it. There are other ways that are probably cheaper, that's just the way we're used to doing it. Or you could just skip it altogether.
I dunno, I think I'd give Gordon a call before I spent $9000 on a software core. But maybe I'm still missing something.
Follow Ups:
Here's my whole line of reasoning on this:
I don't like having a computer in or anywhere near my audio rack. They generate EMI, vibrations, noise etc. Of course you can build fanless no moving part computers and shield heck out of them, but then to get one that can store a terabyte or more of files AND have no moving parts and not emit not much of any EMI is getting tough and expensive. Throw on top some one that wants fancy UI for interacting with the player software with album art, extensive searching etc and you need an even more powerful computer if you don't want any interactions with the music at all.
Why bother with all that? Put the computer in another room, now it can be a regular off the shelf inexpensive computer. In the listening room you have quite a few choices for remotely controlling the software on the big box.
The ethernet connection lets you hook the DAC up to any computer anywhere in the house and use whatever software you want to run on that computer.
If you try and do that with USB you run into length limitations. True you can use an optical USB link, but the "inexepensive" ones don't do high speed, which precludes any 24/192 implementations. A USB link that can do a good job of high speed audio to a computer 100 feet away is NOT cheap.
The part of the system in the audio hardware (the DAC) doesn't need a computer, it fits entirely in an FPGA in the same way that the digital filter you use doesn't require a computer, its implemented with gates in the FPGA. There exits an FPGA core that implements all the necessary IP protocols, but the company charges $9000 for it. (thats a one time fee, not per device, once you pay that fee you can make as many FPGAs using that core as you want).
In order to make this work you DO have to install a program on the computer running the player software. The software works as a virtual soundcard that your chosen player software talks to. Its sort of like using asio4all, only it exists on windows, mac and linux.
The whole concept is to give the user the flexibility to build a system where the pieces are optimized for what they do, a file sever that can just be a file server, it doesn't have to be silent etc, a user interface that can be just a user interface, it doesn't have to store gazillions of bytes of data, and an audio hardware interface that can handle high data rates, allows the DAC to be in control of timing, generates the bare minimum amount of EMI, noise on groundplanes etc, AND does this in such a way that the sound quality is not effected by whats going on in the computer(s) implementing the rest of the system other than the bits being transferred by the player software.
In addition the bandwidth is high enough its possible to implement say a 6 channel DAC for those that want to do triamping for their speakers and run the crossovers in software. The horsepower for the DSP can run on an inexpensive computer in the other room. It can even run on a different computer than the file server or player computer if you want to set it up that way.
I'm not saying its the ONLY way to do some of these things, it implements a flexible system that has a lot of advantages. If you use USB you have to have a computer either in the rack or near it. My contention is that said computer will have a higher chance of affecting the sound quality of the system than the netjack chip I'm proposing.
I don't think its a good idea to implement this right now. The protocols are still being worked out. This system is part of an existing open software project primarily aimed at musicians and studios that need to move audio data around, but I think it has some very good aspects for audiophiles. And even in a full software implementation with a computer at both ends it sounds darned good.
After things settle down a bit I think this will be a very good way of building a distributed digital audio system that sounds extremely good.
John S.
John S.
Just like some folks like integrated amps and others like separates, I can see that a solution like you are proposing could make a lot of sense. We would possibly be interested in offering something like that.
Let me know if there is something we can do to help (we are *really* bad at writing PC software). Or if you figure it out, we may want to license it from you.
Like you said, it is not ready for prime time yet. But in a few months or years, that might be a great solution for a lot of people. The really tricky part is going to come when you are trying to remotely control the computer in the other room, however.
The original Squeezbox had a two-line display that was barely adequate. Now they are migrating to things like the Controller and Touch. I don't like the idea of introducing a Wi-Fi based component in my listening room -- I think it defeats the point of moving the electrically noisy computer to another room. I have an idea for a way around that. Unfortunately, the Squeezebox devices seems to be limited to 96/24 and if there is an upgrade path, I can't see it. It's a shame because it should be trivial to dump 192 down Ethernet.
You've got my e-mail. Please keep me posted.
John,
First there are a ton of new optical USB 2.0 products. You can goto Lcom and take a look. There are also some that work off of 10BT cable and are isolated etc...
But really if you are worried about a computer and EMI and stuff then what do you think an Ethernet server is? Heck most of them probably would not even pass FCC testing A or B. Something every commercial computer would have to qualify for.
I think for Ethernet to really become an audio standard (and it can) is that it needs some easy way to be linked to any computer and or application. While JACK does that, it's not something that holds up under fire. What we need is some prototype setup that developers can have a virtual device driver interface that will allow the Ethernet dac look like a selectable audio output.
Thanks
Gordon
J. Gordon Rankin
> But really if you are worried about a computer and EMI and stuff then what do you think an Ethernet server is? Heck most of them probably would not even pass FCC testing A or B. Something every commercial computer would have to qualify for.
Thus he has addressed and is addressing the above point.
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