PA0SU said:
I have to have another look at my DAC if there might be such a filter.
PA0SU said:
PCM56 is very comfortable with 500mV @ 500ohm / 1mA
PA0SU said:
Not much to amplify here, I use the +6dB TVC to convert from +/- 250mV balanced to 1V SE.
No opamps.
All your mentioned drawbacks apply to real or fake PCM63, that are some of the reasons why I do not use it.
Bernhard said:
Okay, be happy with it. I never understand the objections against op amps....
BTW (a stupid question) what is a 'TVC'?
spzzzzkt said:
Paul,
The missing link is the FIFO. FIFO acts like cushion so your XO tuning will be less proactive. The clock signal in SPDIF usually contains long term shift and short term jitter. FIFO is good to mask out the short term jitter, i.e. spurious noise around the main frequency. Definitely your XO tuning should not react to this, instead, it shall focus on the long term frequency shift.
Another good thing about FIFO is that you can easily figure out the clock shift trend through FIFO's status signals such as 'almost full', 'almost empty', etc, something very hard to do with the simple PIC structure. And remember PIC is a big jitter source itself! Without FIFO, PIC's own jitter will play into the game of judging the SPDIF clock shift.
If the XO tuning circuit were too proactive, you are not reducing the jitter, instead, you are just making things worse! You always have to keep this in mind.
As I have talked about before, the main challenge is still the PIC-DAC-VCXO loop. How linear will the DAC outout be? How accurate is the output voltage? How noisy is it? How will XO react to voltage change? How linear will it be? How will XO behave during voltage change? This loop is tricky to do and can be very expensive to do it right.
This is why people would simply use DDS to replace this loop. They also use FPGA because you can have controller and FIFO put in together. The only down side is that a top DDS chip can easily cost $50+. It also needs a XO running as high as 50-100MHz.
The FIFO/DDS thing usually takes a full month of work for an engineer so dont feel frustrated. Whatever problems you have run into are exactly what others have encountered. It does need some serious work.
My suggestion will be simply ditch this SPDIF thing. Check out this nice I2S solution. And yes, it is available now! Interested? 🙂
Attachments
Re: FIFO/DDS solution for a CD transport
That digital lens thing is a very dumb FIFO solution. Only good for remove some jitters yet cant handle long term frequency shift. Again, an antique techique trying to solve a problem in the wrong way! 😀
There are lots of misunderstandings about receiver chips such as CS8420 and DIR9001. As far as clock recovery goes, DIR9001 is as good as it can be. The add-on jitter is only extra 100ps. The real problem is the signal quality of the input SPDIF. If the signal isnt clean, DIR9001 will not be able to do magic for you. If the signal is relatively stable, DIR9001 will only add extra 100ps jitter above it. So the scenario comes to:
1. The SPDIF signal is clean, DIR9001 will do a job good enough. An extra simple reclocking device may actually get things worse than do any good.
2. The SPDIF signal is bad, DIR9001 will get you lousy output yet a simple reclock device will not be able to pull things back together either.
In other words, if you cant do reclocking right, it will be better off that you pay attention to the SPDIF source instead of wasting time on the DAC.
This is the same with a system with word clock. The DAC part is fair straightforward yet it's very hard to get the transport synch to the word clock correctly.
irgendjemand said:
That digital lens thing is a very dumb FIFO solution. Only good for remove some jitters yet cant handle long term frequency shift. Again, an antique techique trying to solve a problem in the wrong way! 😀
There are lots of misunderstandings about receiver chips such as CS8420 and DIR9001. As far as clock recovery goes, DIR9001 is as good as it can be. The add-on jitter is only extra 100ps. The real problem is the signal quality of the input SPDIF. If the signal isnt clean, DIR9001 will not be able to do magic for you. If the signal is relatively stable, DIR9001 will only add extra 100ps jitter above it. So the scenario comes to:
1. The SPDIF signal is clean, DIR9001 will do a job good enough. An extra simple reclocking device may actually get things worse than do any good.
2. The SPDIF signal is bad, DIR9001 will get you lousy output yet a simple reclock device will not be able to pull things back together either.
In other words, if you cant do reclocking right, it will be better off that you pay attention to the SPDIF source instead of wasting time on the DAC.
This is the same with a system with word clock. The DAC part is fair straightforward yet it's very hard to get the transport synch to the word clock correctly.
regal said:
Gosh, that PLL thing is a major jitter source itself already! And it's even a 5V device! How much propagation delay are we expecting? 😀
tritosine said:
The beauty of HDD player is that you can do 16/44 to 24/192 upsampling on your PC first with tools such as SSRC. You can try as many combinations, as many different parameters as you want to get the best upsampling result before you send the wave files to the player. No more involvement of digital filter. No more bad side effect of ASRC either.
Sure, if the DSP had extra power, you can build your own upsampling function in firmware as well.
Re: Re: FIFO/DDS solution for a CD transport
Nope, nope, you even dont know which FIFO I was talking about. Reading data out of a FIFO? What if the FIFO is empty already? Your reclocking circuit is smart enough to fill in music data automatically? 😀
PA0SU said:
Nope, nope, you even dont know which FIFO I was talking about. Reading data out of a FIFO? What if the FIFO is empty already? Your reclocking circuit is smart enough to fill in music data automatically? 😀
Re: Avoiding the VCXO and reclock before the DAC
Again, an antique solution trying to solve the problem in the wrong way! Hehe
PA0SU said:
Again, an antique solution trying to solve the problem in the wrong way! Hehe
PA0SU said:
See, you have got it totally wrong. The key is the FIFO. You even do not need a VCXO+PLL. You can do it with a DDS with a much better result! 😀
As for the FIFO/DDS thing, you can put it anywhere, before receiver, after receiver, after digital filter, etc. These are just minor implementation differences. Some people feel clock into the digital filter should be low jitter already, some believe it should be the DAC chip. That's it.
Bernhard said:
I totally agree with this. PCM56 is what I call the last, truely bi-polar DAC by BB/TI. It has an excellent 1.2Kohm current output impedance, a relatively long settling time. This means PCM56 can live happily with good OPs.
PCM63 starts to get worse with a 670ohm output impedance then PCM1704 basically is a nightmare.
This is why I really like ADI chips. They in general have better output current source. We had planned to mount D1V3 with AD1862, and still want to...
finneybear said:
sure, maybe even room correction if someone goes that far. As far resampling goes, minimum phase processing can be interesting to try, there are even freeware progs to do that, there is a comparison page about the commercially available algos. Still I'd want the 8x at the end for various reasons, im pretty sure it can be squeezed into the blackfin.
I am interested very much bout the reclock circuit posted. Found the foreign thread already, looks like it can accept AES/EBU with transformer isolation ? Perfect, I'd want 2 and maybe one for my buddy, will let you know, please pm me.
Nikola Krivorov said:
Finney,
Do you have the connection to feverhifi?! I am trying for month to get 2 of THIS I2S parts + 4 of the SM5847 to DF1700 Adapters (the blue one). No answers from them, and I can't buy in Europe from Taobao.... Help!!!!!!!
IJ
lets make a groupbuy thingy then, someone administer it 🙂)
well i have a lynx aes card i dont want to part with, so , even if i have to terminate the xlr into bnc , that circuit looks optimum
well i have a lynx aes card i dont want to part with, so , even if i have to terminate the xlr into bnc , that circuit looks optimum
Entering diyAudio-forum, I knew I would not enter a university. Audio seems to be a religion, so I thought I entered a church but it seems to be a mosque...
Finneybear, You have no bloody idea where you are talking about. Is this the new gospel, or are you a false prophet? Have compassion with an old man who helped developing the CD-player in the early 80-s of the previous century within Philips.
In other words: you totally miss the essence of digital signal processing and digital to analog conversion.
To say it stronger: you are a twaddler, a gossipmonger or a blatherer. At you the choice.
It would not be so bad if you were alone but there seems to be a large group who believes your gospel. I do not argue any more. This is impossible in a non-scientific environment.........
Finneybear, You have no bloody idea where you are talking about. Is this the new gospel, or are you a false prophet? Have compassion with an old man who helped developing the CD-player in the early 80-s of the previous century within Philips.
In other words: you totally miss the essence of digital signal processing and digital to analog conversion.
To say it stronger: you are a twaddler, a gossipmonger or a blatherer. At you the choice.
It would not be so bad if you were alone but there seems to be a large group who believes your gospel. I do not argue any more. This is impossible in a non-scientific environment.........
Paul,
Don't listen to Finney. His only point is to sell that gadget. Plus, shows all the traces of inexperience with such a digital pll solution. You know, I had been the first to signal the need for buffering the incoming data stream - in the other thread. The PMD100 was a good example [for me] to demonstrate the absolute necessity of it. But even without a buffer, I can get good audio for 10-20 seconds, before a synch error would happen! JUST TWO WORD of buffer is enough for all purposes - and it's included in all the crystal receivers!!! And in some of the digital filters.
If you would have doubts, look up the interventions of Gordon, while he was at it - at the beginning he was talking / thinking a lot about FiFo-s, just like Finney, then, once got the thing working, now just says the same - use the two word buffer of a receiver.. So clearly Finney did not try it yet..
So, just go ahead - keep up the good work!
Ciao, george
Ps.: Also, have another look at Jos 's boards - do You see FIFOs anywhere? Only a crystal receiver.. They are not needed, point. I don't need them, as well.
Don't listen to Finney. His only point is to sell that gadget. Plus, shows all the traces of inexperience with such a digital pll solution. You know, I had been the first to signal the need for buffering the incoming data stream - in the other thread. The PMD100 was a good example [for me] to demonstrate the absolute necessity of it. But even without a buffer, I can get good audio for 10-20 seconds, before a synch error would happen! JUST TWO WORD of buffer is enough for all purposes - and it's included in all the crystal receivers!!! And in some of the digital filters.
If you would have doubts, look up the interventions of Gordon, while he was at it - at the beginning he was talking / thinking a lot about FiFo-s, just like Finney, then, once got the thing working, now just says the same - use the two word buffer of a receiver.. So clearly Finney did not try it yet..
So, just go ahead - keep up the good work!
Ciao, george
Ps.: Also, have another look at Jos 's boards - do You see FIFOs anywhere? Only a crystal receiver.. They are not needed, point. I don't need them, as well.
Here is the link of the reclock assembly selling for RMB138 (about $18 usd). I do not understand why the price is even lower than a so call low jitter XO in US or Europe. Also I am sure that selling at this price will no way may the seller rich.
http://www.feverhifi.cn/viewthread.php?tid=1067&extra=page=1
If Audio is not religion, then the price of some poor performing gears will not be able to sell for tens or hunderds of thouands dollars!!! A good example is a cable which can sell few thousands dollars and it is totally "snake oil" to me.
This is human nature that they will say something goods about the stuff they buy, own or use. This is to justify he made the right decision. I am sure sometimes I do the same thing as I am a normal human being.
I think I am the only one in Asia but do not ask me to buy the reclock things.
Spencer
http://www.feverhifi.cn/viewthread.php?tid=1067&extra=page=1
If Audio is not religion, then the price of some poor performing gears will not be able to sell for tens or hunderds of thouands dollars!!! A good example is a cable which can sell few thousands dollars and it is totally "snake oil" to me.
This is human nature that they will say something goods about the stuff they buy, own or use. This is to justify he made the right decision. I am sure sometimes I do the same thing as I am a normal human being.
I think I am the only one in Asia but do not ask me to buy the reclock things.
Spencer
maybe the price is like that cause it meant to be an extension of their DAC pcb. Personally, I wouldnt mind offering more, esp. if we go groupbuy style, such compensation issue can be sorted out easily.
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