Sunday, 1 June 2014

Ethernet vs. USB for Streaming

The Sonore SOtM (Soul Of the Music) sMS-100 is an excellent Network Music Streamer that connects via Ethernet and outputs Aysnchronous USB to your DAC. It supports Vortexbox/LMS SqueezeLite, Apple Airplay, DLNA, and MPD.
In the past those of us streaming digital source material to our music systems have used S/PDIF via Optical or Co-Ax (in fact many still do from CD Transports where resolution is only 16/44 – 16 bit 44 kHz). In more recent years there has been a move to USB as the preferred source for streaming into external DAC (Digital-analogue Converters) devices or Amplifiers and AV Receivers with built in DACs. This has been due to the rise of Asynchronous USB support – and improvements in computer O/S (operating Systems) serving the source data to the DAC. However one question now is whether Asynchronous USB is still the best, or whether network streaming across a (cabled) Ethernet network (or even a high reliability Wi-Fi one) is now the better option?

Should all new DACs’ be expected to feature both a high quality Asynchronous USB interface (that supports at least 24/192 resolution) and a similar high quality Ethernet interface (either with or without Wi-Fi)? Why does this matter? Not everyone needs this? The reason is simply that it (a) provides longevity to the device's usefulness, and (b) ensures the best possible performance from the device at minimal extra cost (and analogy to this might be building the latest model Rolls Royce or Bentley, but deciding to only put in it a Mini Cooper fuel injector or carburettor system – which will work but will never allow the vehicle the option to reach maximum performance if you do choose to 'put your foot to the floor’).
The Perreaux Audiant DP32 Pre-Amplifier with USB DAC has an excellent Asynchronous USB implementation.
Why is or was Asynchronous USB considered so good and in some ways was a key breakthrough for streaming? Normal USB connectivity on a computer is one-directional, and relies on the internal ‘clock’ of the PC – using its bus rate to maintain the signal timing. Unfortunately typical computer clocks’ are a little unreliable and erratic – primarily due to the demands placed on them when a computer has peak loads on its processing. This is a key source of jitter – where the signal gets out of sync and the timing is off… On top of this you have the inherent effect of the variations in power supply and electrical fields inside the computer itself further affecting the clock performance.
Sonore SOtM tX-USB card - an excellent solution for outputting Asynchronous USB 2.0 audio from a computer at resolutions up to 32 bit. The tX-USBexp version adds USB 3.0 support.
The key difference with Asynchronous USB is a separate clock controls (or manages) the data stream. This is usually located with the DAC - and thereby manages the data stream to its own cycle, and not in line with the clock in the computer (hence the term ‘asynchronous’). This ensures (in theory) that the digital music data streams into the DAC in a reliable steady stream, and isn’t fluctuating due to the vagaries of other demands being placed on the source computer;s processor (note the source computer may not be an actual PC or Mac or such, it could be any form of device, like a NAS – Network Area Storage – device that has a computer processor in it). While Asynchronous USB streaming still isn’t perfect, it has up until now provided the most robust method of getting digital music to a DAC & amplifier intact (i.e. without jitter and other unwanted artefacts) – and providing there is no other unwanted influence from the computer source, cabling, or DAC, it provides the most reliable and ‘musical’* data for the DAC & amplifier to process…
Ethernet Cable
Why hasn’t Ethernet been deemed of equivalent quality to Asynchronous USB in the past? Primarily in the past Ethernet connectivity was prone to drop outs, and jitter, much as early forms of digital streaming were (and still are with some devices, including some CD Players, via S/PDIF and such). However this principally related to the implementation – mainly computer (or device) O/Ss’ which didn’t manage the data transmission well, or had overworked clocks, as well as other issues with older Network devices such as switches & hubs.

Sonos was one of the first commercial products to adequately manage streaming via the network (and Wi-Fi) – this combined with improvements in computer O/Ss’ (e.g. Windows 7 & 8 have far superior inherent network interface stability to Windows XP – curiously Linux implementations have always seemed to have a pretty solid network management) has now shown that Ethernet may now be a true equal to Asynchronous USB when it comes to streaming music digitally. And while cabled Ethernet (i.e. CAT5 or CAT6 cable) is preferred, with the newer 802.11n and 5GHz wireless protocol(s) - when used in areas with little or no radio interference - reliable Wi-Fi streaming is also possible via Ethernet.
The Musical Fidelity V-LINK 192 Asynchronous USB Adaptor allows you to convert high-resolution USB to S/PDIF (Co-Ax or XLR) up to 24 bit 192 kHz - for use with DACs that do not support full 24/192 resolution on their existing USB interfaces (or lack USB entirely - this gives the benefit of Asynchronous USB via a DAC's S/PDIF interface).
In the last 12 months streaming via the Ethernet has certainly seemed to come of age, the new series of Devialet (110/170/240/500 – which have recently been upgraded to the 120/200/400/800) amplifiers, for example, appear to have an excellent Ethernet streaming implementation (both wired and Wi-Fi) in addition to a very good Asynchronous USB interface. This augurs well for future implementations and hopefully all new DACs (whether stand alone or integral to amplifiers or music streamers) will support both Ethernet and Asynchronous USB methodologies (as well as traditional S/PDIF), at the best resolutions available (i.e. 24 or 32 bit and 192 kHz or better), for music lovers to utilise.

* By ‘musical’ we mean it does not sound sterile, thin, or stretched – this is often caused by loss of data or more often by the timing being off (e.g. jitter), as much as it can be affected by the DAC's processing itself, in any of these cases tricking our ears into hearing the sound as sterile, bland, thin, and/or the speed of the song as wrong.

Jitter: slight irregular movement, variation, or unsteadiness, especially in an electrical signal or electronic device - typically with audio it will cause drop outs, pops or clicks, and other anomalies. Read more at Wikipedia.

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