Ethernet to Fiber media converters


(Sean) #122

Another way to think about what I’m saying about the optical-to-copper conversion potentially being very noisy… is to consider the Lumin X1

I can assure you the optical-to-I2S conversion process with the X1 (DSD512/PCM768kHz support on their fibre input…) is very noisy and an expensive challenge for their engineers to lower it’s noise AND to isolate this noise from the analogue section… The big advantage here is it’s in their total control and there is virtually unlimited budget to do it very well . Just look at the price of the X1 - but I’m sure you get what you pay for.

But the important part is that converting high speed optical to I2S (or copper ethernet) is no trivial and no cheap task if you want ultra low noise…


(Peter Lie) #123

Actually the SFP module does the optical conversion. We simply provide a SFP slot so that user can plug in a SFP module (similar to the network switches with SFP ports). They can even try different modules to see which sound better. Those SFP modules are generally inexpensive to try, starting from USD7.


(Sean) #124

Ah yes, I forgot about this.

Everything I wrote about about optical-to-I2S conversion applies to ethernet-to-I2S conversion too. No trivial task, especially at PCM768kHz/DSD512 rates that X1 supports on ethernet…

I can maybe count on one hand the DAC’s out there that support PCM768/DSD512 on their ethernet input… which should tell one that it’s no trivial task (for the same reasons mentioned in previous post).


(Magnus) #125

For generic connections to a DAC (not related to ethernet), the best solution would be something like asynchronous Toslink, but with higher bandwidth. No jitter (or not much anyway), and no noise, at least not from outside the DAC. But then I guess there will be noise from inside the DAC in the optical conversion.

Humans flew to the moon 50 years ago, surely we can invent noise-free connections to a DAC chip :slight_smile:


(Peter Lie) #126

Typically toslink has more jitter than coaxial due to the optical conversion. It is not asynchronous. So generally audiophiles stick to coaxial and avoid toslink (before USB audio becomes the norm).


(Sean) #127

Exactly. So the exact same as I’ve been hinting (converting from optical to whatever) applies… it’s not just a matter of using linear regulators and a low noise battery PSU… the conversion process itself is a noise source and not cheap and not easy to do this with ultra low noise.


(Sean) #128

I’m sure NASA could do it, with a NASA budget… but for the budget/price of your Pro-Ject S2 DAC… we’ll need to wait a long while :grin:


(Magnus) #129

Yes, but with coaxial you don’t block electronic noise. But I did say asynchronous toslink (which as far as I know don’t exist), which would takes care of the jitter. In other words, I am just dreaming about stuff that don’t exist :slight_smile:


(Sean) #130

I’m sure if you gave @wklie the moon landing budget, he and his team could do something special !

Or they’d all take that moon landing budget, split it, run and we’ll never hear from them ever again :grin:


(Peter Lie) #131

I don’t think asynchronous toslink exists, but at least the designer of a certain brand of DAC claims he does an excellent job of reducing jitter from it, and advocates the use of toslink with his DAC.


(Magnus) #132

Toslink is nice, better than USB directly from computer (at least on my system), but not as good as using an ethernet transport. But since the DAC is forced to use the senders clocks, it has to be hard (impossible) to get rid of the jitter.


(Sean) #133

Actually two: both Rob Watts and Ted Smith…

Below is Mojo’s TOSLink J-test. So you can see why jitter is of no concern for Rob.


(Magnus) #134

Unless I am mistake (which is likely), don’t jitter tests for Toslink/coax depend a lot of the quality of the sender? If they use synchronized clocks the there is not much jitter problem, but for typical connections there is much more jitter.


(Sean) #135

In the image above Rob says “Tests using 2 uS of source jitter revealed no output change at all, so Mojo is indeed source jitter immune.”

That’s gobs more source jitter than any source you will use at home…

They love TOSlink because jitter is no concern to them and there is zero potential for ground / leakage current loops via TOSlink input. The obvious limitations are sample rates.

Ted says TOSlink is best but he has a lot of DSD128 and higher recordings, so USB is the main one he uses (with foobar).


(Hans Bogaert) #136

Reading all this great feedback, trying to see where it come’s together made me think in a certain direction and please let me know if I’m going the wrong direction.

The FMC are doing a good job however reading the feedback made, it’s only solving a part of the problem for a FMC is not ideal, there’s new noise, there’s jitter and phase issues.
Now I go one step back , I came to the conclusion that when I installed my FMC the impact it has on DSD is way less compared to PCM files. Seems that DSD is less sensitive for all these electrical disturbances. ( based on your feedback in this forum )

The name Ted Smith was dropped and his approach is to convert everything that enters the DAC to DSD. that process is done without decoding.
If you do that then looking at the robustness of DSD for electrical interference are you then indeed eliminating the things we are talking about ? I would therefore no longer hear the impact of my FMC ?
But then if so… why wouldn’t all DAC manufactures follow that route and go for internal DSD conversion ?
is there a simple way to try this out ? connect a network DAC that takes ethernet in and spits DSD out to feed a separate DAC that only does DSD to analog conversion ?

Questions… and more questions are circling my brain :slight_smile:


(Peter Lie) #137
  • Whether DSD is inherently less sensitive to jitter seems to be true in some cases, but is probably not universally true across different DAC or accepted universally. Some people actually believe the opposite is true (as you have proposed before)
  • Conversion to DSD makes the sound signature different - not everybody likes it. If everybody loves DSD you will see all Roon users upsample things to DSD if their DAC support it - clearly not everybody does.
  • Since this is a Room forum, you don’t need the DAC to convert things to DSD for your experiment. You only need Roon (or HQPlayer).
  • Some DAC architecture is not very suitable for DSD
  • There are at least two manufacturers who insisted DSD is much worse than PCM. I respected them for sticking to their beliefs and not making their high-priced products DSD compatible… for at least a while
  • I don’t believe DSD automatically makes fiber isolation irrelevant

(Magnus) #138

I kind of doubt that. Attaching a Mojo to a Chromecast Audio (mini toslink) or to a transport like Allo DigiOne is not going to result in the same sound. As far as I know, Toslink is synchronous so the DAC has to use the clock of the sender (compared to asynchronous USB where the DAC tells the sender what send-rate to use).


(Hans Bogaert) #140

Peter,

Ha, yes you are right there’s no need for separate hardware Roon does that.
With that in mind, I can say that I’ve already done that test and know the outcome
It was my starting point when I joined the discussion.

The debate is then more " DSD to be or not to be" based on what our ears prefers
hmmm interesting.


(Sean) #141

Ah but he isn’t commenting about sound quality at all. He is saying it measures the same with huge amounts of TOSLink jitter (at the limit of the APX-555…)… and he hints that at levels of -160dB, there are bigger issues to worry about than incoming jitter… like ground currents / leakage currents, RF etc…

And your comparison of Chromecast Audio TOSlink with Allo DigiOne is not an apples to apples comparison… one source is RF immune (optical) and ground currents / leakage currents immune - and the other isn’t… so naturally it’s possible they can sound different, if RF interference and ground currents / leakage currents are factors… incoming jitter won’t be the dominating factor in this case (if his APX-555 measurements are to be believed…)


(Magnus) #142

Ah yes, the DigoOne is coax not toslink. But my point is, if jitter is not a problem, and electronic noise certainly isn’t, what makes different toslink sources and cables sound different?