USB yet again
For a few years I have had an Intona Isolator with Oyaide Continental 5S upstream and Intona Reference downstream connecting Streamer and DAC. Given the Strong benefit of filters on the upstream Ethernet connection I added a LHY Audio USB 3.0 purifier with a Grey Knights power cable. The tightening of the transfer and resultant SQ was remarkable despite having used superior cables before.
While USB remains a compromised transfer format, asynchronous USB is the only protocol synchronising the server’s and dac’s clocks unless both have master clock connections. AES/EBU may have better noise rejection but has imbedded clock signal,SPDif is outdated as well as speed constrained and I2S not standardised. Hopefully the industry comes up with a better solution. It is interesting that there seems to emerge a trend to combine server and dac: one wonders why?
I was perfectly satisfied with my Node 130 using USB to my Denafrips Pontus II DAC. Started reading threads like this, and after checking with Alvin Chee at Vinshine, I decided to add a Denafrips Iris DDC between the Node and Pontus. The Iris optically and galvanically cleans and re-clocks the data, and then outputs via I2S to the Pontus. The sound improvement was immediately noticeable even before the Iris and cable had a chance to settle in. Why I keep reading these threads |
On one hand, what shall matter is the final digital to analog conversion, inside a properly designed and manufactured DAC. All those intermediate digital-to-digital converters, theoretically, shall not affect SQ. On the other hand, I keep seeing accounts of SQ improvement after a DDC was inserted in the digital path. Then, of course, we have posts like that on ASR regarding DDC: "I’ve done extensive A/B testing and measurements with these. If properly blind tested, these didn’t make any difference with any of the DACs I tried" What’s going on? Upon closer look, it appears to me that most of such SQ improvement accolades come from owners of R2R DACs. I looked at descriptions/specs/reviews of three of them, which I encountered most often in users testimonials: https://www.denafrips.com/specs-enyo https://www.denafrips.com/specs-pontus https://www.denafrips.com/specs-terminator-plus All three use "Proprietary USB Audio Solution via STM32F446 Advanced AMR Based MCU". What is STM32F446? Here is the spec: https://www.st.com/resource/en/datasheet/stm32f446re.pdf What counts the most from my perspective is the CPU performance of that chip. It has one core, frequency of up to 180 MHz, and instruction efficiency of 1.25 per clock. So, it is roughly an analog of Intel Atom processor operating at 0.225 GHz. Pretty slow. The chip’s price reflects this - less than $10 per unit in quantity: https://www.mouser.com/c/?q=STM32F446 Let’s pick some cheap contemporary oversampling DAC and see what kind of CPU it uses. For instance, S.M.S.L Sanskrit 10th MKIII, which can be purchased for $139. It uses XMOS XU-316 chip. Here’s its spec: https://www.epsglobal.com/Media-Library/EPSGlobal/Products/files/xmos/XU316-1024-QF60B.pdf?ext=.pdf This chip is quite a bit more advanced. It is not same yet similar to the one used in $17,500 https://www.suncoastaudio.com/products/aqua-hifi-formula-xhd-dac. It is approximately equivalent to Intel Atom processor operating at 2.4 GHz. That is, it is over 10x more performant than the chip used by the Denafrips DACs. Please note, I’m not discussing chips used for digital-to-analog conversion per se. The chips I discuss are used to deal with USB protocol, and to presumably implement First-In-First-Out (FIFO) buffer for the digital samples, enabling their subsequent re-clocking. Could it be that the Denafrips DAC has to use a simplified FIFO buffer? Either in terms of length, responsiveness, or something else, because their CPU performance is less than 10% of that of a cheap contemporary oversampling DAC? I tried to find measurements of the Denafrips DACs that could shed some light on that. Turns out that in Non-Over-Sampling mode (NOS), objective measurements of one of then are not exactly impressive: If such distortions were mostly a consequence of the DAC architecture with not overly precise resistors used, then insertion of DDC wouldn’t likely improve things - it wouldn’t affect resistors. Since the DDC insertion does improve things, there is a reason to believe that the excessive jitter caused by the limited FIFO implementation might be at play. Or perhaps something else related to timing precision. If this hypothesis is correct, than the DDC effectively adds a good implementation of FIFO in front of the DAC, thus ameliorating the DAC’s FIFO imperfection. Please note that this is just a hypothesis. Would like to hear your opinions about this. |
@sns Totally agree, but I think I’d substitute “delight” with “unbridled opportunity.” I mean, this stuff can just get better and better almost seemingly without bounds if you’re willing to put in the thought, effort, and $$$. @vthokie83 My experience running an Iris into my Musician Pegasus absolutely mirrors your experience. Immediately noticeable and this with a cheap little 6” Monoprice HDMI cable. Amazing, although maybe our DACs are set up to be optimized with the i2S input so I have to submit that as a variable. Maybe other DACs prefer other inputs, but I’m all in on i2S. |
Fair, You have some logic to the reasoning, but is above my understanding of electronics. I do know that the reports I have seen (or witnessed in my system) with a DDC or re-clocker working well were all from R2R ladder DACs, but from several different manufacturers (Denafrips, Musician, Holo Audio, and a couple more). Whether it is due to a FIFO limit, or the benefits of I2S, or some other reason I cannot say. Soix agreed, I tested a friend's Pegasus and Aquarius in my system, and the results were the same.....but as before they also would have benefitted from I2S. If you're thinking of upgrading your HDMI, my reference is an Audioquest Vodka 48 8K, but the Supra Cables 2.1 8K and DHLabs HDMI 2.1 10K sound great as well.....both under $100 |
