XMOS-based Asynchronous USB to I2S interface

[1audio]

Originally Posted by barrows

Is that most SPDIF receivers are poor perfromers at best, adding 200-300 pS of jitter. The Coax output of the WaveIO is transfomrer isolated, right? So I expect that the differences you note are down to the improvement of avoiding SPDIF. My experience has been that well implemented I2S direct to the DAC chip will outperform SPDIF every time.

Not always. SPDIF can have vanishingly low jitter. Here is a plot (similar to Stereophile) of a $25 DAC from e-bay Assembled DAC 2496 (AK4396) CS8416 DAC Board 24BIT 192K | eBay that has about 10 pS of jitter at 180 Hz (if my arithmetic is right). I modded it with an input transformer and more supply filtering. It still needs some more obviously. .

There are other examples of better dacs with less jitter using conventional SPDIF interfaces. And a decent spdif interface will have pretty good isolation.

[labjr]

The problem with SPDIF is aligning two clocks. I can't see why anyone would use SPDIF unless there was no alternative.

[1audio]

Originally Posted by labjr

The problem with SPDIF is aligning two clocks. I can't see why anyone would use SPDIF unless there was no alternative.

I think that's a little naive. SPDIF really has one clock and very sophisticated schemes have been developed to extract the clock cleanly from a data stream. I think execution is more important than core technology.

Async USB brings a number of potential benefits, but it has challenges as well and isolation on USB is a real bitch. Also the USB clock doesn't line up well with 44.1 based clocks (two clocks in USB as well).

For clock isolation transformers are much lower jitter than opto or other isolators. Use a D-latch to resync the data, word clock and bit clock. Use the back side of the master clock going into the DAC chip so everything has settled before the chip samples the data.

[rsdio]

Originally Posted by 1audio

SPDIF really has one clock and very sophisticated schemes have been developed to extract the clock cleanly from a data stream.

SPDIF has one clock if you're happy settling for a 'push' technology. According to Dan Lavry, an external clock will never be superior to a properly-designed internal clock, and the only logical conclusion from there is that 'pull' technology is the better choice for jitter-free clocking. Thus, you really have two clock - one at the media source and one at the DAC. The problem is that 'pull' requires two-way communication, and SPDIF does not offer that unless combined with additional technology (even if it's just another SPDIF link back to the media source).

I think execution is more important than core technology.

That's easy to say, but the challenge is that SPDIF uses both rising and falling edges for clock, and yet no digital clock technology has identical rising and falling specifications. Thus, jitter is different for rising and falling edges, and it's data-dependent.

Async USB brings a number of potential benefits, but it has challenges as well and isolation on USB is a real bitch. Also the USB clock doesn't line up well with 44.1 based clocks (two clocks in USB as well).

That's completely irrelevant. It's perfectly workable for USB packets to carry a different number of audio samples per frame. The async nature of the link means that even irrational ratios between various clocks in the system are not a problem.

I would also suggest that every DAC involves similar challenges of linking the digital and analog sides of the conversion without allowing digital noise in the analog outputs. USB should not really make this any worse unless shortcuts are taken.

[Ken Newton]

Originally Posted by 1audio

Not always. SPDIF can have vanishingly low jitter. Here is a plot (similar to Stereophile) of a $25 DAC from e-bay Assembled DAC 2496 (AK4396) CS8416 DAC Board 24BIT 192K | eBay that has about 10 pS of jitter at 180 Hz (if my arithmetic is right). I modded it with an input transformer and more supply filtering. It still needs some more obviously. .

There are other examples of better dacs with less jitter using conventional SPDIF interfaces. And a decent spdif interface will have pretty good isolation.

What was the S/PDIF source/transmitter used to make that plot?

[labjr]

Originally Posted by 1audio

I think that's a little naive. SPDIF really has one clock and very sophisticated schemes have been developed to extract the clock cleanly from a data stream. I think execution is more important than core technology.

Async USB brings a number of potential benefits, but it has challenges as well and isolation on USB is a real bitch. Also the USB clock doesn't line up well with 44.1 based clocks (two clocks in USB as well).

For clock isolation transformers are much lower jitter than opto or other isolators. Use a D-latch to resync the data, word clock and bit clock. Use the back side of the master clock going into the DAC chip so everything has settled before the chip samples the data.

The DAC clock has to be aligned with SPDIF clock so technically there is two clocks in the system which have to be synchronized. And that's the problem. You can't slow or speed up the data flow. SPDIF needs to be retired for good

With Async USB there is no clock. It's just packets of data until it is clocked out of the USB receiver using a precision oscillator in the DAC. Simple and it works well. Wavelength does both Async and SPDIF converters and Gordon Rankin will tell you the same thing.

BTW Optical Thunderbolt cables may solve isolation problems.

[Jogi]

O.K., finally I had time to figure out how to get the WAveIO working. Trying to set up voyage I managed to destroy my Linux OS, had to set it up again twice and ended up with the new Linux Mint 13 with Liquorix Kernel. Seems that with older Linux OS the XMOS chip is not recognized, at least in my case.
I use the SPDIF connection to a AD1865 dac with C3g/Lundahl LL1660 output stage; I tried both the isolated and non isolated output, the non isolated does not work somehow. A little PCB with the AKM4396 chip is in the drawer already for experiments with I2s.

But I am not in a hurry, because this combination already sound really fabulous! Before I used a heavily tweaked Teralink, and it is no contest comparing the two.
Luciens board sounds much more natural, spacious and relaxing, it is spooky sometimes...and no trace of "digital" sound, vey musical. Even the PRAT thing is there, and very clear positioning and lots of details without sounding "detailed".
I would say, this is the best hundredsomething bucks I've spent in a long time for audio.
First I tried to run it with external power via a Salas Shunt, but it ran out of steam. This board is really power hungry, I didn't have a heatsink big enough to get more juice out of the reg. I took a normal linear supply with 2A then, and it gets really hot.
I also tried a ADUM isolator, but it was not recognized by the computer using this. Maybe it is also some power issues, have to find the reason for this.
Again big thank you for Lucien, from a happy camper...

[shoom]

''Luciens board sounds much more natural, spacious and relaxing, it is spooky sometimes...and no trace of "digital" sound, vey musical. Even the PRAT thing is there, and very clear positioning and lots of details without sounding "detailed".
I would say, this is the best hundredsomething bucks I've spent in a long time for audio''.

I totally agree with the above.
Sounding pretty wonderful with my Buffalo3
A real bargain
Thanks again Lucien

[bigpandahk]

Dear Lorien

You got PM, I want to purchase a WaveIO board.

Thanks

[Lorien]

@ bigpandahk: you have PM, thank you!

@ Jogi: it's nice to see that it end up well in the end Could you share your experience with WaveIO and Linux on PM or using this thread and draw a path for other guys in using them together? The point is that I'm willing to make some sort of user manual for this card and now I'm gathering all kinds of infos related to using WaveIO with OSes other than Windows - the one that I'm used with. Any help here from any of you guys will be really appreciated!

@ JensH: I am considering the path of moving oscillators to the isolated side for some quite time now but what keeps me still is the fact that I want this change to be available for all users (including those that already own a WaveIO). It's some sort of "must be" and I'll not give it up unless I have no other choices. Well, for now it proves to be challenging for me as long as the moods required to accomplish this task are not easy to be made by end user without proper equipment and some soldering skills but I'll continue to dig in...

Kind regards,
L