Uac2 4 and 6 channels, UK USB-i2S boards

[ben Sharp]

Hi Guys sorry if this has already been covered i am new to the forum and couldn't see it obviously. I am looking a designing a couple of analog boards for the usb-i2s widget and have a couple of questions .

1) has any one explored more than two channels ? Is it possible using the widget? I believe this is possible using Usb audio class version 2? I want to replace my current sounds card with hifi quality USB DAC but was considering using it for my surround too and i didnt like the sync issues of 3x USB linked DAC`s!

2)  i am looking at using WM8740/8741 or the PCM1792 configured in Mono mode so two dacs for stero to get best perfomance. I am also possibly going to look at an opto isolated version.

3) Does any one the uk supply the usb-i2s boards?


4) has any one tried adapting the firmware to below Atmel evaluation kit? It looked like a cheap, easy, quick way for me to get started. 
http://uk.farnell.com/atmel/at32uc3a3-xpld/kit-eval-us3-a3-xplained/dp/1972188

Thanks
Ben

[Alex Lee]

On Saturday, 22 September 2012 22:59:57 UTC+8, ben Sharp wrote:

1) has any one explored more than two channels ? Is it possible using the widget? I believe this is possible using Usb audio class version 2? I want to replace my current sounds card with hifi quality USB DAC but was considering using it for my surround too and i didnt like the sync issues of 3x USB linked DAC`s!

The Atmel based USB-I2S module cannot support more than 2 channels at 192/32.  It is not a limitation of UAC2.  It is a limitation of the Atmel hardware at the I2S end.

We have been looking at an 8 channel USB-I2S design.  It requires a new uController and most likely an FPGA for the I2S interface.  There are commercially available 8 channel devices so you can google for them.  However, you need to carefully evaluate:

1.  How is the master clock setup and used?  How good is the jitter in those designs?

2.  How good is the I2S isolation (especially against ground loop and PC/USB digital noise)?

3.  Are they true UAC2 devices, or do they require custom drivers from the vendor?  If custom drivers, are they available for Linux and OSX as well?

 

2)  i am looking at using WM8740/8741 or the PCM1792 configured in Mono mode so two dacs for stero to get best perfomance. I am also possibly going to look at an opto isolated version.

Good ideas !!!!!  Please experiment and let us know the SQ.

I believe opto-isolation of the I2S and good isolated power supplies to the DAC and the low jitter XO's etc. are key to SQ.  Borges has a draft design of an isolated USB-I2S module. 

3) Does any one the uk supply the usb-i2s boards?

Only from Borges in Norway.

 

4) has any one tried adapting the firmware to below Atmel evaluation kit? It looked like a cheap, easy, quick way for me to get started. 
http://uk.farnell.com/atmel/at32uc3a3-xpld/kit-eval-us3-a3-xplained/dp/1972188

No.  The Atmel evaluation kit will probably NOT work without hardware hacking as the pins required for connecting the two low jitter XO's to clock the I2S are not compatible.

[ben Sharp]

Thanks Alex,
Thats great, I have wondered a few times about using an
arm based SOC chip with multiple I2S interfaces running Linux as a
network sound card / media player with possibilities for crossovers
etc using brute FIR or similar but that's all dreams atm, it also just
crossed my mind if the Linux gadget Frame work supports UAC (client
device) it could also be a usb sound card. It might be an interesting
avenue to look at for a multichannel device . For now i shall build a
AD Board based on dual wm8740 and see how it sounds i think some
cleaver trickery in the analog domain with differential outputs and
virtual earth might be enough to get over the horrible PC earth loop
issues and noise but i will experiment and report my findings. I use
gEDA on linux for my hardware design are there any Gschem symbols or
gEDA / PCB footprints available for the USB-I2S interface pin headers
to kick start my AD board design i have a 4 hour train journey
tomorrow and want to get stated ASAP.

> >http://uk.farnell.com/atmel/at32uc3a3-xpld/kit-eval-us3-a3-xplained/d...

[bossesand]

http://www.minidsp.com/products/usb-audio-interface/usbstreamer here is a commercial version for 125USD looks resonably compleet.

If it can be done cheaper it would be great but otherwise ? I need at least 4 input channels and 4 outputs.

 

The Atmel based USB-I2S module cannot support more than 2 channels at 192/32.  It is not a limitation of UAC2.  It is a limitation of the Atmel hardware at the I2S end.

We have been looking at an 8 channel USB-I2S design.  It requires a new uController and most likely an FPGA for the I2S interface.  There are commercially available 8 channel devices so you can google for them.  However, you need to carefully evaluate:

i1.  How is the master clock setup and used?  How good is the jitter in those designs?

2.  How good is the I2S isolation (especially against ground loop and PC/USB digital noise)?

3.  Are they true UAC2 devices, or do they require custom drivers from the vendor?  If custom drivers, are they available for Linux and OSX as well?

 

4) has any one tried adapting the firmware to below Atmel evaluation kit? It looked like a cheap, easy, quick way for me to get started. 
http://uk.farnell.com/atmel/at32uc3a3-xpld/kit-eval-us3-a3-xplained/dp/1972188