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-   -   XMOS-based Asynchronous USB to I2S interface (https://www.diyaudio.com/forums/digital-line-level/188902-xmos-based-asynchronous-usb-i2s-interface.html)

labjr 17th November 2011 05:26 PM

Russ White, for one, says there is no disadvantage to using a single crystal clock because of the Sabre's Time Domain Jitter Eliminator thingy. Dustin Forman of ESS says pretty much the same thing. Gordon disputes that and said Dustin actually agreed with him. An ASRC, no matter how good, always acts like a a filter and can not completely eliminate jitter. I guess it depends how fussy the user is about jitter.

barrows 17th November 2011 07:09 PM

Actually...
 
If one reads Russ White's most recent comments on the subject, he has noted that he really likes using the ESS 9018 with synchronous clocking, and he has noted that Dustin agrees.
It may be that in dialing in his own XMOS USB receiver, Russ has achieved low enough jitter to get synchronous mode sounding really good.
My experience is that the real issue here is not jitter per se:
Most DACs which use ASRCs do so because the ASRC does reduce measured jitter artifacts at the analog outputs (this is how Benchmark, and bel canto can get good measured jitter specs using adaptive USB).
The problem is, that the ASRC comletely resamples the data by complex mathematics, all the original samples are discarded and replaced with the new interpolations (unlike the integer based oversampling which occurs in the DAC chip itself, which preserves the original smaples). Additionally, the commonly used parts for ASRC are limited in processing power (unlike sophisticated SRC programs like Izotope, which use more complex math to achieve better results) and must operate in real time during playback. My opinion, is that the ASRCs used in many DACs, are simply not up to the challenge, and by their conversion, add significant (non musical) artifacts not present in the original data.
So, if one can provide a very low jitter data stream to the DAC, it is advantageous to use synchronous clocking, to avoid the problems caused by the ASRC, since we no longer need to "reduce" jitter at the DAC, as it is already very, very low.

To get back on topic: this is one reason why low jitter interfaces, like Lorien's, are so important: we can have low jitter at the DAC, without having to use "jitter reduction" techniques which cause other damage to the sound.

rsdio 17th November 2011 11:54 PM

Quote:

Originally Posted by barrows (https://www.diyaudio.com/forums/digital-line-level/188902-xmos-based-asynchronous-usb-i2s-interface-post2785556.html#post2785556)
To get back on topic: this is one reason why low jitter interfaces, like Lorien's, are so important: we can have low jitter at the DAC, without having to use "jitter reduction" techniques which cause other damage to the sound.

This is what it's all about! :-)

triode_al 23rd November 2011 03:11 PM

Lorien, a few questions.
Product looks like what I am looking for! The stock reference design from XMOS is cool but it is closed while I see your board as open and thus catering to my wishes of being able to tinker around a bit.

1) is the board populated & soldered? I have mostly seen empty boards in the start of this thread!

2) Can I connect to the I2S with a Philips-version of the I2S protocol, a TDA1541-43 based DAC or is it the Sony such as PCM58-63, or is that selectable?

3) I can't go higher than 18 bit in my DAC. That is no problem of course.

4) Can I improve the onboard clocks? (In the reference design XMOS L1 I could easily do that I think by piggy backing a doubled up TENT clock board.) I like to be able to do a later upgrade.

5) Does your XMOS implementation do selectable upsampling (&interpolation)?

I em'd you at ekits (at) luckit . biz, that is correct?
albert

Lorien 24th November 2011 06:02 PM

Hello triode_al,
1) board will come fully populated and tested. Most of the parts are in SMT technology... some of them hard to solder without proper equipment.
2) WaveIO will source digital audio in 32-bit I2S format from which only 24 bits are used for audio data. From what I know, TDA will work but the data will be truncated.
4) I could leave the WaveIO card without oscillators mounted on it to be easier for you to test other master clock sources.
5) It's supposed to be bit-perfect so there's no processing techniques applied to the sound. WYSIWYG.
Yes, my email is as posted above.
Kind regards,
L

Turbon 24th November 2011 11:47 PM

No intentions to half the price?

Brgds

Wolfsin 25th November 2011 01:27 AM

Today izThanksgiving, not April Foolz!
 
Quote:

Originally Posted by Turbon (https://www.diyaudio.com/forums/digital-line-level/188902-xmos-based-asynchronous-usb-i2s-interface-post2794008.html#post2794008)
No intentions to half the price?

That's more in keeping with April 1st :rolleyes:

Lorien 25th November 2011 09:09 AM

Quote:

No intentions to half the price?
That's more in keeping with April 1st :rolleyes:
Not quite! Keeping the prices at affordable level for DIYers it's not new to me though 50% off does not even offer the chances to acquire all the parts needed to assembly the card... I could do that if I would choose ordinary parts and build this board in large quantities (10k or more)... so, from my perspective only XMOS have better chances to fulfill your demand :).
Kind regards,
L

regal 25th November 2011 09:36 AM

Quote:

Originally Posted by Lorien (https://www.diyaudio.com/forums/digital-line-level/188902-xmos-based-asynchronous-usb-i2s-interface-post2793687.html#post2793687)
Hello triode_al,

2) WaveIO will source digital audio in 32-bit I2S format from which only 24 bits are used for audio data. From what I know, TDA will work but the data will be truncated.

L

Unfortunately the LSB also gets mangled, so its not bitperfect for the older DAC's. Unfortunately I think this is a unirversal issue all asynch usb with the only exception being the proporitary Rankin firmware (not a plug more a cry for help as I hate the idea of hacking up a Legato to build an asynch USB-I2S TDA1541 DAC.)


Which leads me to unother question, those of you using the Xmos's clock to synchronously clock the Sabre DAC, do you have to share the xmos board's ground with the DAC's ground ?

Lorien 25th November 2011 03:19 PM

Not necessary. In WaveIO's case, if isolated I2S output port is used then master clock can be provided using AC-coupled LVDS signaling though, this is not available if non-isolated outputs are involved.


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