Optimising optical: converter, SFP module and cable choices

[jandersonhill (Jeremy)]

@miguelito

I think the argument is there are 10x more of those transitions per second and thus more electromagnetic noise

Yes, agree that is absolutely possible

@miguelito

Those bit transitions are happening all the time regardless of whether you’re sending audio data

Thanks, @miguelito. I’d forgotten 100Base-T upwards did that

[Ermos (Erno)]

@miguelito

Well let me ask this:

Why is there a loop port at 100mbps, with its own separate controller? I mean, why bother at all?

What is the use of this port especially given the slower speed and the fact that the controller is set up in parallel, ie it is completely equivalent to the 1g connection?

What exactly is a loop usecase? Put a computer on a slow connection?

Hi Miguel,

What I know is that the StreamUnlimited Stream800 network board inside the dCS networked part has this:

Interfaces/Connectivity
• SO-DIMM 200 board edge connector
• Wi-Fi 802.11b/g/n (dual band, WoWLAN)
• Bluetooth
• Ethernet 10/100 Mbit/s (WoLAN)
• RGMII for 2nd Ethernet or alternative Wi-Fi
• SDIO interface (SD card, alt. Wi-Fi, etc.)
• 2x USB 2.0 (1x OTG) with iPod digital audio
• GPIOs, LCD
• Control interface to carrier board (I2C, SPI)
• Digital audio interfaces (I2S, SPDIF)

The loop port Ethernet 10/100 Mbit/s (WoLAN) has Wake-on-LAN. The RGMII for 2nd Ethernet is the main ethernet connection at 1000mbps. Reduced gigabit media-independent interface (RGMII) is a standard which was developed to reduce the number of signals required to connect a PHY to a MAC. Reducing pin count reduces cost and complexity for network hardware especially in the context of microcontrollers with built-in MAC, FPGAs, multiport switches or repeaters, and PC motherboard chipsets.

[miguelito (Miguel Barrio)]

Ok understood. But again, why bother exposing this at all? Adding an Ethernet jack is higher cost.

[Ermos (Erno)]

For quick reference dCS does not support any of the following:

• Managed Ethernet switches
• Use of the Loop port on Rossini / Bartok to daisy chain another device
• Optical media converters
• “Bridged” network configurations

For more information please read on…

[Mosaic FAQ] Unsupported network configurations

Unsupported network configurations with dCS products Trouble-free function of our streaming products relies on a number of underlying networking technologies working properly. We find that most typical home networks work fine with our products, but there are some configurations which are known to cause problems. Rather than go into a technical discussion of proper network design we want to point out a few configurations which are known to cause issues. For quick reference dCS does not support …

[miguelito (Miguel Barrio)]

Even more reasons why this is an option that’s intended to allow you to force a lower speed ethernet.

[PaleRider (Greg)]

Good stuff from folks who know a thing or two. Thanks Erno.

[TheFlash (Nigel of Reiki Audio)]

@Anupc

@TheFlash

SFP or SFP+

Other than the difference in bit-rates involved, it won’t matter, not to the bits anyway.

Also, contrary to the claims by some Audiophile Switch vendors (e.g. Innuous), 10G/SFP+ have better (lower) noise characteristics, due to the significantly higher transmission rate involved.

@TheFlash

Multi-mode or single-mode

Some audiophile make preposterous claims online. It makes absolutely no difference in the home context.

Please don’t forget first principles to which you yourself agreed, the bits are not changing, and noise doesn’t travel over optical fibre cables!!

Laser diodes associated with single-mode transmission are generally more expensive, but has the potential for much further reach (up to as much as 40km) because of the lower dispersion of the wavelength over single-mode fibre. Whereas multiple-mode lasers are much cheaper, but transmissions incurs significant dispersion and thus has a much shorter reach.

None of this has any consequence to the bit error rate, and no consequence in the home environment.

@TheFlash

Wavelength

The typical optical SFPs used in audio are what’s generally known as “grey optics”, typically 1310nm and 1550nm. They’re standard wavelengths defined by the ITU and IEEE for 1G/10G optical transmission.

You can also BIDI optics (combines and TX and RX onto a single fibre instead of a pair), as well as coloured optics (CWDM and DWDM optics with a very wide range of frequencies); designed for multiplexing multiple 10G wavelengths onto a single pair of fibre via optical couplers. But none of these have any real use in most home environments.

@TheFlash

Makes/models

Finisar (now II-VI) are one of the World leaders in pluggables, and are in fact a key OEM supplier to many vendors. Some audiophiles who claim one SFP is better than another don’t actually realise that many of the SFPs are in fact identical, just branded/labeled differently

More to the point, please don’t forget first principles to which you yourself agreed, the bits are not changing, and noise doesn’t travel over optical fibre cables!! SFPs and optical cables have no impact to sound quality. Impacting sound quality goes against basic physics and engineering of how these things work. Those who claim to hear otherwise, are IMHO delusional

Basically then, and tell me if I paraphrase you inappropriately, optical is optical: as long as “stuff” is standards-compliant, bits sent = bits arriving so all the options here are equal over typical home distances in a typical home setting. Sound quality won’t/can’t be impacted by the choices made. In the digital domain I obviously believe you…

So no need to worry about SFP vs SFP+, single vs multi-mode, or wavelength.

This is the basic optical kit I bought to try it out many months ago, but life just gets in the way… can any of this be improved on in the digital domain? (I have to add the qualifier “in the digital domain” for obvious reasons). Digitally, my Amazon optical patch cord will perform as well as its Corning counterpart… unless you suspect sloppy production controls and lax standards compliance of course.

[Ermos (Erno)]

@miguelito

Even more reasons why this is an option that’s intended to allow you to force a lower speed ethernet.

In case you haven’t read it, dCS say:

The Loop port operates at 100Mbit/sec and was never designed to be used as a general-purpose network port. We have encountered some issues with customers using this port to connect a server, NAS, or other general purpose device. Due to the speed differential there can be issues with network flow control which will cause instability.

Edit: BTW, my managed switch (unsupported of couse by dCS), easily allows me to set the port speed, so if you like to limit it to 100Mbit/sec, use your switch to limit it, but not the Loop port.

[miguelito (Miguel Barrio)]

Right. But the point they are making is don’t use it as a loop port to connect another device to your network (frankly the name implies you could). I have had zero issues using the Loop port instead of the 1gbps port - that is what they are talking about when they speak of speed differential.

[Ermos (Erno)]

@Ermos

The Loop port operates at 100Mbit/sec and was never designed to be used as a general-purpose network port.

@Ermos

my managed switch (unsupported of couse by dCS), easily allows me to set the port speed, so if you like to limit it to 100Mbit/sec, use your switch to limit it, but not the Loop port.

Can you try this, comply with the specs, and fulfil your desire?

[Anupc (Anup)]

@miguelito

What are people’s views on using 100mbps or 1gbps ethernet? The argument for lower speed seems to be that the electromagnetic noise put out is lower

Gigabit Ethernet circuits are far more sensitive to noise than 10/100. So, the very basis of that statement is wrong as Gigabit Ethernet systems are typically less electrically noisy than traditional 10/100 ones.

[Anupc (Anup)]

@TheFlash

optical is optical: as long as “stuff” is standards-compliant, bits sent = bits arriving

Yup.

@TheFlash

This is the basic optical kit I bought to try it out many months ago, but life just gets in the way… can any of this be improved on in the digital domain?

Just the one Media Converter? Does your Ethernet Switch have an SFP cage that you’re connecting this Media Converter to? Not a lot can go wrong, just be sure to match the SFPs on either end, and to the appropriate fibre type.

@TheFlash

Digitally, my Amazon optical patch cord will perform as well as its Corning counterpart

Yup. For home use, meaning even meters of it, no difference whatsoever. In fact, even if you happen to mismatch the SFP type to fibre, for example, attaching multi-mode fibre to a single-mode SFP pair (or vice versa) , it’ll work just fine at home.

[TheFlash (Nigel of Reiki Audio)]

@Anupc

@TheFlash

This is the basic optical kit I bought to try it out many months ago, but life just gets in the way… can any of this be improved on in the digital domain?

Just the one Media Converter? Does your Ethernet Switch have an SFP cage that you’re connecting this Media Converter to? Not a lot can go wrong, just be sure to match the SFPs on either end, and to the appropriate fibre type.

No, a pair, the other one is adjacent in the box but out of sight

[ChrisK]

Nice, but it is still designed to work on Earth, it would work even better in space, far from the radiations of a solar system

[TheFlash (Nigel of Reiki Audio)]

So @Anupc, I think you’ve covered off most of the parameters/options folk seem to wrestle with when working out how to implement optical for audio networking purposes. And the answer seems primarily to be that as long as everything is standards-compliant then it will work and we shouldn’t worry about much of what we read others worrying about…

I guess in some ways this is an echo of the views expressed you’ve expressed elsewhere about bits being bits, and it would be difficult to argue with this. However, you also mentioned on a few occasions the importance of using high quality/low noise power supplies on eg media converters. So please allow me to add this to my opening list of considerations in the same format:

Power supplies/external
What difference do various external power supplies make to optical circuits? I tend to default to linear PSUs rather than quiet SMPS’s, though I know there are advocates of the latter.

How important are power supplies and why?

Power supplies/internal
Same Q here I guess, as there may be media converters with internal PSU’s. If you look inside say an ADOT media converter vs the 10Gtek ones I have here, there are bigger caps and no doubt other stuff going on.

All input gratefully received.

[miguelito (Miguel Barrio)]

Well, if you consider each transition producing an amount of electromagnetic noise regardless of the number of transitions per second, then it would make sense that there would me more noise density with 1gbps than 10/100mbps.

The fact that the circuits themselves don’t get affected by noise as much as 10/100 is different from the noise they can produce.

[miguelito (Miguel Barrio)]

@Anupc

@TheFlash

optical is optical: as long as “stuff” is standards-compliant, bits sent = bits arriving

Yup

Nope. In SPDIF the clock must follow the source, and if there’s low frequency drift in the source clock them you can get audible jitter.

[Anupc (Anup)]

@miguelito

The fact that the circuits themselves don’t get affected by noise as much as 10/100 is different from the noise they can produce.

In fact, it’s both, more sensitive to noise, and the produces less noise. Go ahead and do some research on it.

@miguelito

Nope. In SPDIF

Dude, the thread is about Optical SFPs. Not TOSLink.

[Anupc (Anup)]

@TheFlash

Power supplies/external
What difference do various external power supplies make to optical circuits?

Not specifically to the optical portion of the SFP, to the electrical portions, i.e. the other end of the SFP and the rest of the Media Converter, as well as to prevent a cheap [PSU] from spewing noise back to the AC supply.

@TheFlash

Power supplies/internal
Same Q here I guess, as there may be media converters with internal PSU’s

Not sure I follow. The ADOT has an external PSU doesn’t it? Or do you mean the regulators inside the Media Converter?

[TheFlash (Nigel of Reiki Audio)]

Thanks again.

Sorry, the ADOT does have external PSU but the innards (regulator board) seem pretty beefy compared with the 10GTek. I wondered whether this might be a factor in the sonic difference reported by some and the preference they’ve expressed for the ADOT. We agree it can’t be any difference in the digital domain, so it’s either (a) in the power supply element or (b) in the imagination. Try to resist!