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In Reply to: RE: Absolute Sound on Auralic Vega PLL posted by soundchekk on February 17, 2015 at 00:26:17
I thought it clear what I wrote. It is certainly possible to use the SABRE chips in a way that they require accurate clocks, but if the ASRC is used correctly they will lock on to inaccurate sample rates. The on-chip SPDIF receiver logic will still have some limits on signal jitter, measured well into the nanoseconds, because there has to be an open eye pattern. It is certainly possible to botch a design and get terrible signal integrity.
I'm not surprised that DIYers have trouble making the chip work. Apparently even some manufacturers have this problem as well. (I am talking about making it work, not sound good. That's another question entirely, because of the 100 Mhz clock circuitry involved.)
I know how these decoders work. I've designed and implemented them in the past, albeit at much lower signaling rates and clock speeds. But you're right: the SABRE chip documentation is somewhat cryptic. I assume you read and understood the white paper and also the various patents. Were I to design a product around this chip the first thing I would do would be to play with the chip on a bread board and discover how it really works. This is a huge PITA. Back in the day I was designing circuits and software to decode comms data I had access to the actual logic diagrams of the hardware and additional details, such as clock tolerances. I don't DIY, because I was used to working with a fully equiped hardware lab and access to all documentation. But I can see that people will run into problems if they get over their head.
Tony Lauck
"Diversity is the law of nature; no two entities in this universe are uniform." - P.R. Sarkar
Follow Ups:
''don't DIY, because I was used to working with a fully equiped hardware lab''This is not a reasoned statement. You don't do it because you don't want to.
On the issue of PLL, you are out of your knowledge or comfort zone.
Edits: 02/18/15
Fred,
I see no point in playing with inadequate tools. I don't have the space to set up a proper hardware lab and the test equipment needed would cost more than my audio system.
Have you fixed your scope yet?
Tony Lauck
"Diversity is the law of nature; no two entities in this universe are uniform." - P.R. Sarkar
I don't DIY, because I was used to working with a fully equiped hardware lab and access to all documentation. But I can see that people will run into problems if they get over their head.
Phew. Where's Molière when we need him?
Ever tried reading this (and other such stuff of yours in like vein) in front of the mirror before posting it here? Go on. Give it a try.
D
Par ma foi ! il y a plus de quarante ans que je dis de la prose sans que j'en susse rien, et je vous suis le plus obligé du monde de m'avoir appris cela.
Tony Lauck
"Diversity is the law of nature; no two entities in this universe are uniform." - P.R. Sarkar
il y a plus de quarante ans que je dis de la prose sans que j'en susse rien
Yeah, yeah, I'd guessed you'd know your Molière (and your Google). It was your magnificent, almost magisterial, pomposity I was drawing attention to. This is a hobbyists' forum FFS - let's lighten up a bit.
Go on - you know you can do it.
D
Read that in high school French class over half a century ago. Connection to Richard Strauss came later.
Tony Lauck
"Diversity is the law of nature; no two entities in this universe are uniform." - P.R. Sarkar
Hmmh. I havn't seen any Sabre implementation DIY or commercial, which
really worked well without putting in major effort in front of the DAC.
I read all the flashy promises about that chip. That's why I bought it too.
No question. If well implemented the Sabre chips sound really good. I do have a problem with the marketing message around the "patended Hyperstream" feature.
Cheers
The "patented Hyperstream" feature refers to the sigma-delta modulator. See the White Paper. There was also a video one of the designers gave on this subject. Interesting, because there were artifacts that some audiophiles heard that the designers didn't and that didn't show up on the measurements. As a result there were further improvements made in the modulator, presumably in the chip.
The biggest design challenge with the chip is the very high clock rate and the necessity to have very careful PC board layout and power for the chip and associated clock circuitry. I suspect this is one place where many designs go wrong. However, there are still some issues with the chip that require work around to get the best sound.
First, the ASRC needs to be bypassed, assuming the clock problems can be handled elsewhere. It's better than other ASRCs but it is not a complete solution since it is not bit transparent. At the very least, there is cross talk (admitted in the white paper) from the SPDIF input circuitry that makes it through the chip via ground bounce, etc., and pollutes the analog output. So even though "all" jitter may be removed by the ASRC there will still be input effects.
Second, the upsampling filters (particularly for Red book) are poor, just like almost all filters built into DAC chips. These need to be effectively bypassed by upsampling elsewhere, either in the DAC itself or in the computer. I upsample in the computer, e.g. to 176.4 or 192 before sending PCM to my Mytek. There are much better filters that can be selected, either by system balancing or (better) by adjusting to music genre or individual recording.
Third, the Hyperstream modulator is not as good as it might be. Many people have found that using Miksa's HQPlayer modulator to convert to DSD128 produces better sound than sending high rate PCM to a SABRE chip based DAC, such as my Mytek. Miksa claims he has some spectrum plots that show that his modulator has lower distortion, but I've not seen them. Unfortunately, Miksa's modulator is very compute intensive and some people may find their CPU speed to be a limiting factor.
This is just my personal take on this, and I have attempted to reach conclusions based on improvements when using my Mytek Stereo192-DSD DAC. There were a number of other tweaks that were needed to get around limitations of this DAC, especially bypassing the analog volume control circuitry and using the internal jumpers to reduce the output voltage. This enables me to go direct via balanced XLR to my amplifiers while needing very little digital volume reduction in the ESS chip, i.e. no bits in the input signal are lost at the settings I use for playback.
Tony Lauck
"Diversity is the law of nature; no two entities in this universe are uniform." - P.R. Sarkar
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