Intro
Contents
Every link in the hi-fi chain counts. Energy, sources, acoustics, the rack, the ears … and…the network. We’ll take a look at a few different solutions. Including single mode and multi mode fiber optics.
In the 21st century, streaming has become the most common way to listen to music, this is true even for hi-fi enthusiasts. Listening to the market around me, the general opinion is that it may be a little easier to achieve good sound quality with CD or vinyl, but the convenience of streaming and the huge selection available through streaming services often wins out.
Streaming does require a bit more effort to achieve the same quality as CD, for example, there are many factors within the digital circuit that can affect the quality of the final analog signal. In this review we are going to highlight one of them: the network connection, and specifically the wired one.
Bluetooth is a possibility, but because a Bluetooth receiver itself generates a lot of noise, it is not the most obvious choice for good quality. Add loads of compression and you get the point.
Noise level
In a network for high fidelity streaming, basically everything is aimed at keeping electrical noise, which unintentionally and inevitably travels along with the electrical square wave of ones and zeros, as low as possible. After all, noise can affect the clock of the streamer or the DAC, resulting in jitter. There are several ways to bring this noise level down, the simplest being a passive filter with a good RJ45 cable from the filter to the streamer. Another option is a high quality switch and from there again a good cable to your streamer. You can improve the switch with a linear power supply and if the switch and streamer allow it, you can create a galvanic connection with fiberglass.
SFP connection and fiber optics
SFP stands for Small Form-factor Pluggable, the connection is designed to make switches flexible. There are both copper and fiber versions of SFP modules. And they come in a variety of speeds.
Pluggable means you can plug in the module (if the switch has a slot for it). And – depending on the module – various cable types are possible: singlemode fiber, multimode fiber, copper (UTP, FTP, S/FTP) and also, for example, direct attach copper (DAC for short, yes indeed confusing).
As we know, fiberglass is very popular because it can transmit a lot of data quickly, and has high reliability and stability. The advantage for us audiophiles is that the data are transmitted with light, giving you galvanic separation and (virtually) no electrical noise.
Multimode versus Singlemode fiber optics
So what are the differences between multimode and singlemode fiber optics? Multimode has a larger core, 50 or 62.5 µm, light passes through the fiber via multiple paths and uses an LED as a light source. Multimode is cheaper than singlemode and is generally used for shorter distances, less than 500 meters. Singlemode has a smaller core of ~9 µm and the light passes through the fiber via 1 path straight through and has a laser as the light source. It is more expensive than multimode but can cover up to tens of kilometers of distance. Singlemode is theoretically the recommended option for us audiophiles, multimode does also create galvanic separation, but because singlemode has a smaller diameter there is less interaction of the light with the wall of the fiber and this leads to less “pulse edge jitter.”
Transceivers
If you work with fiber you always use SFP transceivers, these are the modules that convert electricity to light and vice versa, quite impressive for those little things. You plug the transceivers into the SFP connector of the switch, for example, and at the back you insert the fiber optic cables, there are always two, one for outgoing data and one for return. The transceivers are specific for singlemode or multimode and therefore not interchangeable.
I can imagine that these SFP transceivers may still affect the audio quality, but there is remarkably little information on that on the Internet, zero reviews found and thus seems to be some unexplored territory. The singlemode set we are testing here from Adott are, according to the manufacturer, specially selected for audio purposes but that’s about it.
Direct Attach Copper
If you can choose galvanic separation, why would you still choose a DAC cable? Well, the theory is this: with fiber optics, you will first have to convert the data from electrical to light and then from light to electrical again, and you might prefer not to have these conversions sitting right in front of your streamer. A DAC cable connection is less complex, less chance of interference, disadvantage is that it’s not galvanic separation, you’ll have to bring down the noise level some other way.
Network is so rewarding to work on! First added a netgear after the famous switch livestream, then an ethernet filter and now a psu for my netgear, what an amazing series of improvements it was! It’s staggering.
Basically it’s better
Probably not on the same level as these options, but wondering how single box units that change rj45 Ethernet to fiber – then back to Ethernet – compare? There are a few out there. Ifi comes to mind, but I think another that was put out there and reviewed by iiwi reviews was the effe-01.
You know you could look at the packets and see how many re-transmissions are happening with various setups. Not that I think 1s and 0s are the only thing, but error rate can effect the endpoint of any network system. Isolation is probably just as important.
From what I’ve tested, the best results were obtained with single mode fiber OM2 (yellow jacket), grade B LC connectors (aka “low insertion loss”) with UPC polish style (there’s PC, UPC, and APC Polish Styles that are not working best if combined). The actual fiber material sounds different from brand to brand, the fiber length determines the attenuation of the signal so shortest is best.
On the transciever side for best results you need 1310nm wavelength, industrial temperature (85 degrees Celsius … vs 70 degrees on commercial ones … I suspect the lens does not deform so much from the heat) and <=10km reach distance. Of course the transmission power and receiver sensitivity add more complexity here, but generally 1310nm + industrial temperature is the final goal, the differences are pretty negligible between brands.
I’ve used fiber in my local network for the audio path for about 3 years, experimenting with media converters, SM and MM fiber and transcievers. It sounded clean, detailed, with extended bass. One day I tried again copper and realized that the fiber sounded thin and it was missing some “air” (the brilliance range of frequencies).
I then discovered DAC cables and I was a bit skeptical because of the “lack of galvanic isolation” propaganda. You can look at DAC cables as being a kind of i2s (no signal conversion, minimum possible latency). The downside is the signal attenuation and the shortest cable is the best one. At the moment I use a 0.15m SFP28 DAC cable between my 2 SOtM switches before the streamer, and sound is snappier, more fluid and has more air and stage extension than the SM fiber I used to have to “clean up” the signal. Regarding DAC cables, I couldn’t find so far a way to DIY some cables using better (pure silver) wire, you have to rely on the manufacturer and the same silver plated OFC for drying your washed clothes.
For RJ45 Ethernet and fiber, read about serialization and transmission latency, the preparation phase (serialization) takes 2400x more time than the actual signal transmission (for each packet), then you add more latency at the receiving end and you’ll get bigger chances of things to go wrong. Oh, did I mention that within the fiber the signal transmission speed is lower by ~10% than in the copper medium? You add reflections and diffraction and you end up again with some imperfect medium (remember TOSLINK? it’s also fiber and offers galvanic isolation).
Hi Arno, this is a very interesting test and I think there’s certainly not enough on the internet for one to anticipate the influence this stuff has. I for one am still blown away by what a simple switch does and you guys at Alpha are at fault here. Your previous test is responsible for my house having 20 switches stored in a drawer. Network cables also play a very real and immediately discernible influence. Unfortunately I never experienced a system where fibre trumps good cooper but, then again, I don’t think I ever heard one with good fibre.
If you search the internet, you do get huge forum threads about types of fibre (Corning glass usually mentioned as giving the best results) and certain transceivers (Finisar is usually mentioned). It’s such a rabbit hole and not clear enough (for me at least) what form factors there are and go with what that I just stopped my hifi network thing here.
But I did invest in a good network infrastructure (two routers, one dirty side switch and a Matrix SS1 with Shunyata cables at the end) because to me it does a very significant difference. Doesn’t make much sense but it is very real. Cheers!