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Old 24th May 2010, 10:15 AM   #1
sampler is offline sampler  Lithuania
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Default Ultimate USB to I2S interface

This thread is a result of non succeeded GB on M2TECH OEM I2S interface, that showed a great demand for a product like this. It’s purpose is to came up with good alternative and create new GB in the end.

The paramount things in product design we need:

- Asynchronous USB (device as clock master)
- Two separate low-jitter VCXO for 44.1k (22.579) and 48k (24.576) sampling derivation.
- Working bit-perfect (ks) drivers for Windows (XP,Vista,7).
- Good documentation/support from manufacturer
- 192 kHz 24 bit I2S output
- Pricing range ~ 50Eu (75$)

Preferable things we need:

- As currently no technical solution for 480 Mbit/s USB2.0 isolation exists (only upcoming isolators from AD?), I2S isolation (optical with high speed cmos optocouplers like HCPL-7723 or digital/inductive as ADuM3440 or better ISO7240 – 1ns eye pattern skew jitter declared)
- Very customized drivers that are managing to stay within 150Mbit/s USB limit, and isolating at USB side (it is doable, at least in theory)
- No onboard PSU, connection for external
- Slaving to external clock (clocks) on “clean” side via isolation (if that is reasonable, as any isolation will introduce it’s own jitter)
- Drivers support for Mac, Linux.
- I2S modes selection

Current candidates:

Musiland 01 MINI
+ Price ~60USD
+ Good manufacturer updates and support, HDCD decoding
+ Well documented mods
- Only one clock

XMOS USB Audio 2.0 Reference Design Kit
+ All paramount objectives satisfied
- Price

+ Well documented mods
+ All paramount objectives satisfied
- Price

XtremeUSB XD1014 EVB
- Only one clock ?

DIYAudio own design using XMOS XS1-L1 128TQFP
+ Fully open source project
+ Just 8$ for bare chip, all other money goes to PCB and top notch parts
+ Already available reference design that works
+ Onboard shunt supply’s could be added
+ Possibility to interface with any dac of your chose, without any glue logic
+ Opportunity to make things right, once and for all
+ Etc…..
- Time?

Let’s discuss our options here.
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Old 24th May 2010, 10:36 AM   #2
EUVL is offline EUVL  Europe
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Link to downloadable software from xmos :

XMOS - Software

Xmos discussion forum :

Index page | XMOS embedded processors. Heart of XMOS technology, XCore.com

Xmos reference design, incl. hardware details :


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Old 24th May 2010, 09:14 PM   #3
Tolu is offline Tolu  Germany
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One negative point to add for M2Tech Hiface:
- no ASIO-support!

So, no use for special audio players like cmp² etc. and no ideal solution for XP user.
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Old 25th May 2010, 03:46 AM   #4
regal is offline regal  United States
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Originally Posted by sampler View Post
- As currently no technical solution for 480 Mbit/s USB2.0 isolation exists .
Wireless USB 2.0 480Mbit/s exists.
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Old 25th May 2010, 08:20 AM   #5
sampler is offline sampler  Lithuania
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Originally Posted by regal View Post
Wireless USB 2.0 480Mbit/s exists.
Yes, I'm aware of that. 480Mbit/s is on paper only and far from reality. IME using both wireless ends 802.11n compatible, will yield 130-150 Mbps at best in real world environment using 5 GHz band. Maybe it will be enough ? We still don't know real bandwidth demand for these products.

I agree, it probably would be better choice in terms of GND cleanness, then PC.
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Old 25th May 2010, 08:42 AM   #6
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You should turn i2s into LVDS anyway to have any meaningful distance between the relatively short USB cable and the converters.
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Old 25th May 2010, 09:18 AM   #7
UnixMan is offline UnixMan  Europe
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IMHO, removing the USB connection to add a (relatively) powerful RF digital RTX isn't such a great idea.

If you're looking for alternatives, ultimate isolation could be done using some optical link (e.g. Gigabit Ethernet on fiber) instead of USB. Unfortunately, that would require some supporting hardware which in the end will likely look a lot like another computer. So the noise we're trying to get out of the door will get back in by the window, so to speak...

Isolation on I2S (with clock on the "clean" side) should be just fine. And we can get away with standard technology (USB 2.0 async audio) that in the long run will be natively supported by all OSs, so our device will eventually become easily "plug & play".
"We should no more let numbers define audio quality than we would let chemical analysis be the arbiter of fine wines." N.P.
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Old 25th May 2010, 10:16 AM   #8
anbello is offline anbello  Italy
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Also "normal" 100Mb ethernet on TP is galvanically isolated with transformer

a solution could be to use the XC-2 Ethernet Kit from XMOS coming with example software available as source code for:
- 10/100 Ethernet MAC/MII driver code
- TCP/IP and UDP stack
then adding some i2s ports using this should be a simple task.
With relatively little effort we could have an interface that take a stream of n channel PCM audio via ethernet and outputs it as i2s ports.
The cons are that in this way we have something non standard (as an USB audio class) but maybe this could be overcome by implementing a standard streaming protocol like UPNP for which there are plenty of HW and free SW implementation of the server, controller and renderer components.

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Old 25th May 2010, 10:24 AM   #9
anbello is offline anbello  Italy
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Sorry but rereading my post i realize it is OT, the title is "Ultimate USB to I2S interface" and not ETH to I2S

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Old 25th May 2010, 07:07 PM   #10
sampler is offline sampler  Lithuania
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I think we should stay open minded here, so all alternatives are welcome.
Biggest drawback of ethernet based solution is functionality. If someone would came up with a wise software , that would allow this device to function as external sound card (thus supporting all players etc.) it would be perfect.

Some thoughts about optical isolation. There are more optical buses then just ethernet. One such an example could be MOST, that is used by AUDI MMI and other car manufacturers for their hi-fi audio-video systems. I have done some repairs to MOST based amplifers/MMI's and can tell that this interface is not another pc Basically only optical converter and programmable MOST interface chip. Obviously not a lot of most familiar programmers around here, but such options exists.

Btw, audiodesign posted XD1014EVB pinout, reposting it here. No more technical details is available for the moment as I understand.
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