Audio Computer Recipes: 2011 Edition

Eighteen months is a long time in computing. Since we last published DIY audio computer recommendations, solid state drives have fallen in price, Android has risen to a genuinely useful platform, and tablets have finally come of age. Along the way, we've abandoned Linux because of lingering stability and compatibility problems with the DACs we most wanted to listen to, and had our ears opened more than once to the shockingly pervasive effects of power supply noise. We also revisited an old favourite, with surprising results . . .

Therefore, this year's recommendations begin with the always great-sounding Dell Mini: lean, silent and sitting on a real sweet spot with regard to power and 'cleanliness'. Removing the hard drive as ever is the big leap forward, but development of the Stealth Mini showed how far the Mini can be taken. Thanks to its Silent Mode support, the dual core Samsung N550 netbooks offer a more powerful 45nm alternative to the Dell Mini for only a few dollars more.

This year's entry-level desktop sees us move away from Zotac to Gigabyte motherboards because of their superior construction quality where it matters. We're big fans of the new Crucial M4 SSDs and LianLi HTPC cases, and still think that a cheap linear PSU + PicoPsu is the best way to get a quick and easy DIY desktop audio system off the ground. It's now headless, naturally: the readily available and surprisingly fast Advent Vega makes the perfect ten inch remote. For admin, the Vega can run full RDP, but for playback only, all that is needed is the light and lovely Gizmo app: no system overhead and very swift. We also discovered CAT7 ethernet wire: more screening and gold-plated connectors: what's not to like?

The most exciting news is perhaps the development of the Advanced Desktop – many features of which are about to show up in this year's DAT1 upgrades: some of which we owe a debt to the developers of cPlay; others to the good people of Audio Asylum, and some of which are all our own work. The new, all-linear PCs, featuring some new wrinkles, sound surprisingly (shockingly) better than last year's models. Also check the new forum threads for discussions of DIY system building . . .

Four digital transports you don't need to buy from us

In many ways the common PC is the perfect digital source: widely available, built to push bits, cheap for large libraries (storage for 2500 CDs currently costs £45 / $75), easy to use as 'streamer' and 'player' and universally compatible with all music formats: infinite jukebox, internet radio, SACD and Bluray player – all in one.

In other ways, especially focusing on their performance as audio devices, the common PC is a real headache. It knows many excellent ways to seriously screw up the performance of your system. Although the processor is a smart bit of technology, everything else about the computer is poverty-spec: mass-produced with the cheapest possible components.

Obviously, when we talk about storage, bits are bits. Thanks to robust error-checking, the computer can be trusted implicitly to shunt files across a network or in and out of memory without changing any of those noughts to ones. Printers don't need fancy USB cables to render accurate output. Enough said.

However, real time digital audio is very, very difficult to do well – which is why top-notch CD transports were rare and expensive. Lots of very easily disrupted processes are happening faster than you might appreciate at smaller scales than you may think.

Motherboards and operating systems produce digital audio as a by-product: they are not designed to deliver low-jitter, electrically 'clean' bitstreams in real time to an audio system largely consisting of boxes that amplify current fluctuations, so it shouldn't surprise us that they do that badly. If we think of the computer as a glorified CD platter (which is surprisingly helpful) it 'simply' has to deliver noughts and ones to a Digital-Analog Converter (DAC) that turns bits into volts, data into music.

Let's zoom in on that interface for a moment . . .

Every DAC has a transceiver/clock assembly that greets incoming data from the computer. Think of this as a doorman. His job is to impose order on the jittery bistream before it can meet the all-important converter chip. He takes it for granted that the right noughts and ones are knocking on the door (bits are bits, right?). His – crucial – job is to ensure that the gaps between them are consistent – that every single bit is temporally 'aligned' to land precisely on each tick of the clock.

Imagine him fishing noughts and ones from the incoming bitstream and spiking them onto the teeth of a cog-wheel spinning at millions of revolutions second. Tough job. Especially as the data arrives at a similar rate. And he's working in a room smaller than a pimple. At these scales, everything matters – even the metallurgy. Although in many cases the computer doesn't apply 'clocking' to its output, any clocking stage is somewhat input sensitive: the computer can make life easier or harder for the doorman and that will show in the quality of his work.

As might be imagined, our superhuman nano-doorman is operating close to (in fact beyond) the limit of his ability: he's pretty highly strung. He's such a diva that he can only do his job properly in perfectly controlled conditions: he requires a very specific temperature, and absolute efficiency in his environment. More than anything, he can't tolerate noise. The slightest whisper of noise causes him to randomly lob bits at the wheel heedless of where they land. The converter doesn't like that.

The mains lead connecting the DAC to the wall is like a soundcar parked outside his open window. The conductive cable connecting your PC motherboard to the DAC's digital input is like a long didgeridoo with one end implanted in the doorman's ear. You couldn't imagine a more efficient way to deliver noise to where it least needs to be. At this scale, your computer sounds like a Godflesh gig happening at the other end of the pipe. Electrical noise produced by the motherboard, its power supply, and all the devices connected to it – as well as radio frequency and EM noise carried on all the unshielded wires and traces – are quite disruptive to the transceiver and clocking sections of the DAC.

Extensive auditioning has proven to developers worldwide that audio systems are highly revealing of any alteration made in hardware or software that impact on a computer's electrical output (up and downstream) and wideband jitter characteristics – both of which factors inter-relate. All this leads to a few guiding principles for computer audio development:

1. Keep it clean. Remove all sources of electrical noise: particularly cheap switching power supplies and spinning hard drives. Simple motherboards with the best possible grounding plans are best. Think carefully about the interaction between everything you connect mechanically. Shield everything.

2. Keep it simple. An operating system and motherboard are designed to do a million jobs: we need ours to do one well: wield Occam's razor ruthlessly: pare away all software and hardware not absolutely needed. Avoid over-powerful processors. Undervolt, underclock.

3. Wide pipes . . . devote maximum resource to the job of delivering audio to the DAC.