A network bridge in its purest form is essentiallya digital audio connection away from the computer that connects to this computer over a network.
Let’s have a closer look.
Basically there are two ways to play musicfrom the internet or from your computer over your stereo: connect your computer directlyto a digital input on your stereo or use a network player.
The problem with connecting a computer toaudio equipment is twofold: the clock signal that sends out the digital music data usuallyis of low quality and the ground plane carries a lot of electrical noise.
These two can cause severe distortion duringthe digital to analog conversion in your stereo.
It is possible, applying a number of tweaks, to reduce both artefacts by using an audiophile power supply, using an audiophile USB on PCIcard that uses an external audiophile power supply and so on.
The alternative is to use an external interfacethat is built to audiophile specifications and connect that to the computer over an asynchronousconnection.
There are two ways of sending digital audiofrom one device to another: Isochronous and asynchronous.
SPDIF, AES/EBU and TOSlink are isochronous, meaning that the sending device – the computer in this case – sends a steady stream of bitsto the receiving device – in this case the DAC.
The DAC has to follow the incoming streamof data, meaning that irregularities in the stream due to a poor performing oscillatorin the source is also followed by the DAC resulting in jitter.
Asynchronous connections don’t use a fixedspeed.
The source sends packets of data and the receivingdevices stores the data in a buffer.
When the buffer is full, the receiving devicesignals the sending device to stop sending until there is space again to receiving data.
It then signals the sending device to sendnew data.
In other words, the clock timing of the sendingdevice – the computer – has become irrelevant after the data has been received by the receivingdevice.
Two asynchronous connections are used foraudio: USB and ethernet.
USB knows many modes and two modes are usedfor audio.
Audio Profile 1 uses isochronous data transportand Audio Profile 2 uses asynchronous data transport.
It might be clear mode 2 should be used forhigh quality audio.
Unfortunately all USB connections need tohave a 5 volt DC line too, to activate the USB port on the receiving side and this voltagecan – and almost always will – cary electric noise from the computer.
Some DACs powers this function of the USBinterface chip internally but this means that the computer will not recognise the DAC untilit is switched on.
The network connection doesn’t cary anyother electric signal than needed for the bits to be transported.
And network connections, true to IEEE 802specifications, should have galvanic separation through small transformers.
Still small anomalies occur through commonmode signals.
The network bridge is a device that is connectedto the computer over the network.
And since ethernet works asynchronous, thecomputer’s clock signal quality has become irrelevant.
Music player software that is enabled to usenetwork bridges sends the music data not to the SPDIF or USB output of the computer butto the network bridge using packets of data.
The network bridge receives these packets, stores them in a buffer and plays them out against its own clock.
The quality of this clock forms the basisof the quality of the digital signal sent to the DAC.
But there are other factors too.
I have spoken of a digital signal where Ishould have used the term ‘analog signal representing bits’.
For what we normally call a digital signalis an analog square wave.
And not even a perfect analog square wavesince such a square wave requires an unlimited bandwidth.
Even under the most ideal conditions thisis not obtainable while real life conditions are far less optimal.
In my video “Connecting your DAC #2: how digitalcan go wrong” I describe how that works for SPDIF signals but the principle is thesame for all digital signals.
So how can a network bridge do that betterthan the computer? To start with, a computer is not built forhigh-end audio application as where a network bridge is.
A computer is a powerful machine using oneor more powerful processors that will generate a lot of electric noise, polluting the groundplane.
And the cheap crystal clock oscillators generatea lot of phase noise that causes jitter in the digital to analog conversion.
A well designed network bridge basically isa computer too, but only as powerful as needed for its task.
Therefore it demands far less power makingthe use of an audiophile, low-noise power supply affordable.
Furthermore the electronics used for generatingthe digital signal to be sent to the DAC will be designed with audiophile demands in mind.
What software can use network bridges.
Most network bridges accept several protocols.
For instance the Squeezebox protocol can beused.
It needs the installation of the free LogitechMedia Server program – LMS for short – on a computer or NAS.
Versions for Windows, MacOS, Linux and thepopular NASses are available.
The music is chosen on the computer directly, on another computer – like a laptop – or using an app on a mobile device.
Another popular protocol is DLNA and it’stwin brother UPnP AV.
In practice it works roughly the same as theSqueezebox format.
You install a DLNA or UPnP AV server programon a computer or NAS and select the music to play using a computer or mobile device.
There are many server programs available forany OS and a great deal of them are free.
Nowadays audiophile music players like JRiverMedia Center and Audrivana 3+ support DLNA network bridges, which they call network renderers.
Roon has its own protocol, named RAAT andmany network bridges support it under the label Roon Ready.
A network bridge that is Roon Ready is oftencalled Roon Endpoint.
HQPlayer, a player that is specialised inaudio processing, has a proprietary protocol too and names network bridges Network AudioAdaptors, NAA for short.
Apple Airplay can also be used as protocol, although it is limited to a maximum sampling frequency of 48 kHz.
The basic idea of a network bridge is ‘adigital output at distance’.
Most bridges use USB Audio Protocol 2, likethe SOtM sMS-200 and the Sonore Rendu series.
Some offer SPDIF and TOSlink too, like theLindemann Bridge.
But more and more other devices integratethe network bridge function into their products.
Many network players can also function asnetwork bridge.
For instance all Bluesound products can functionas Roon Endpoint as can the Auralic Aries series of streamers and many others.
Then there are streaming DAC’s like theMytek Brooklyn Bridge that are DAC’s with a network bridge integrated.
There also are amplifiers and AV receiverswith network bridge built-in like the Advance Paris Playstream A7 I reviewed recently andmany AV receivers by Arcam, Denon, Marantz, Yamaha and others.
Those that like the Raspberry Pi as basisfor their audio player can also use it as a network bridge or streaming DAC.
There is a large choice of sound cards andthere is software for about any protocol you can think of.
Using a good network bridge will result ina clearly better audio quality, compared to a computer directly connected to the DAC, with perhaps the exception of costly audiophile computers.
The analog quality of the digital signal is- within broad limits – of no consequence as long as the signal remains digital butis of great importance during the digital to analog conversion.
I will soon get back on this in a separatevideo.
So the use of costly femtosecond precisioncrystal oscillators, clean ground planes, ultrafast flip-flops and very good circuitboard design all lead to a cleaner digital signal and thus a better functioning DAC, resulting in a better sound.
Also watch my video “An introduction toplaying high quality music files”.
It will be no surprise that taking care ofthe digital signal this way does cost money.
Therefore the best network bridges will costsignificantly more than a simple setup using a Raspberry Pi.
But compared to the digital audio output ofa normal computer – being it SPDIF, TOSlink or USB Audio 2 – any decent network bridgesounds better.
The same goes for network streamers from specialistfirms too.
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