Review: Avid HD I/O

SLICE & DICE

In my mind I often compare audio resolutions to a meat slicer. To my ear, the highest DSD resolutions replay a recorded sound with all its three dimensions preserved. As the resolution drops the meat slicer whirrs into action, sheering the back edge off the signal to produce a shallower and shallower signal until eventually, at the lowest resolution, things sound flat, distorted and decidedly two-dimensional, making it virtually impossible to see deep into the mix. To me, this is why compressed low-res formats have succeeded in convincing the great unwashed of their sonic equivalence. To the untrained ear the processes these formats employ seem less damaging of things up front than things hiding in the background. MP3s are, if you like, the butcher’s equivalent of pressed deli meat… but I digress.

My A/B blind test wasn’t always successful, however – a humbling process for any engineer, even when the process occurs in the privacy of your own home studio. When I tried to concentrate on the midrange and top-end I occasionally failed to pick the new converter over the old one, particularly in circumstances where mixes were fairly solidly compressed or light-on for bottom-end content. In those situations it became more of a guessing game: straws were clutched at, shots were fired in the dark and hope was pitted against hope. It was only when I listened to fairly open and dynamic material again that the differences between the HD I/O and the 192 I/O were noticeable once more.

Overall I’d say the main sonic improvement of the HD I/O over the 192 lies in its extra dynamic power down low. The effect is almost akin to increasing the sample rate of a signal: things get slightly bigger and more transparent and good mixes seem to open up that little bit further, allowing you to see through to the back wall or horizon line, though again, I’d stress the difference is marginal. There’s also a sense of the midrange being slightly smoother and more refined through the HD I/O, but it’s very hard to say whether this is an indirect result of the extra support provided by the increased bottom-end or a fact about the midrange in and of itself.

A WORD ON PHYSIQUE

Physically speaking the HD I/O converters appear – on the surface at least – little more than a rebadged Digidesign 192 I/O. (In a century where the earth’s rotation appears driven more by political spin and companies pedalling their wares than gravitational forces, I’m sure there must be countless ProTools HD users out there jumping to this conclusion.)

Under the bonnet, however, the HD I/O has undergone quite a significant rebuild, though the structural layout of the unit remains much the same internally to reflect the similarity of the rear panel connections between old and new models. There’s a new toroidal power supply, the analogue signal path has been reworked to improve specs and headroom, and changes have been made to the physical layout of both the analogue and digital audio cards themselves. A few of the connection points on the back panel have also been shuffled around slightly and there are two notable absentees: the Legacy port has been ditched – no great loss there really – along with the second set of calibration points that once allowed you to setup each device with two A/D and D/A calibration scales rather than one. These were then selectable via the Options menu in the software, giving you two level input and output sensitivities. The removal of this capacity seems somewhat puzzling and I’m sure there will be more than a few users who’ll miss this feature. I know I will. The fragile DigiLink connection point has also been changed to what’s now called a ‘DigiLink Mini’. It’s no less fragile than its predecessor unfortunately so care must be taken whenever you’re fiddling about with this crucial cable. There’s also a new built-in soft-knee limiter called ‘Curv’ (selectable via a little drop-down menu inside the ‘Analogue In’ tab of the Hardware Options menu) that’s designed to allow you to track hotter signals into the unit, though with a dynamic range of 122dB (A/D) I’m not sure why you’d want to. At the very least, this extra limiting option is handy as a protection mechanism against the dangers of firing your audio signals into digital hyperspace without a helmet.

INCREASED I/O

While all these changes and improvements on the HD I/O unit are commendable, arguably the most significant improvement beyond all others is simply a quantitative one – everyone likes more of something after all, unless you’re counting golf strokes perhaps. To that end the new HD unit now comes in three basic flavours: the HD I/O 16×16 Analogue (featuring 16 analogue inputs and 16 analogue outputs); the 16×16 Digital (featuring 16 channels of AES/EBU I/O, 16 channels of TDIF I/O and 16 channels of ADAT I/O, with supports for S/MUX II and IV); and the 8x8x8 (which is a combination of analogue and digital I/O). The previous 192 I/O only possessed eight channels of inputs and outputs as standard, to which you could always add eight analogue or digital ins or outs to the equation of course (though not simultaneously), but this also came at a significant extra cost. From a basic conversion standpoint therefore, and irrespective of the sonic differences, you now get more for less. Furthermore, the new HD I/O boxes are expandable even further with a range of additional HD Option cards, although the 16×16 analogue option already comes full to the gunnels on the rear panel – if you want to customise this unit you’ll first have to decide which card is for the chop.

SKIN DEEP?

It seems somewhat ironic that Avid has chosen such an understated outer shell for the new HD I/O. Avid claims this modesty was mainly to allow old and new models to co-exist in a rack without one looking radically different to the other. Unfortunately, all that appears to have changed is the name and the colour of the plastic trim, and for mine this new guernsey doesn’t appear to be doing the unit any favours. There was, apparently, a “more radical” version of the hardware secretly floating about at one point that was subsequently ditched because beta testers found it just a little too offbeat looking. I would like to have seen this version, although on balance – and all cynicism aside – the changes to the faceplate are approximately equivalent to the sonic changes: the two units are similar, but not the same.

In hindsight the improvements to Avid’s new ProTools HD converters are about what I’d expected, although they’re manifestly at the opposite end of the spectrum from where I assumed I’d hear them. I figured the new model would be clearer, particularly in the super top-end but it’s mostly down low and front-to-back where the biggest changes appear to be. Although the differences are very subtle at first, they become clearer as you grow accustomed to the new light they shed on your audio. Mixes seem bigger, deeper and slightly more powerful than the identical mix played back through the 192 I/Os. That alone may be enough of a carrot to edge users – myself included – over the line as I’m sure this perception will only grow stronger the longer I use them. The downside is that the new incompatibility issue means I’m now looking at a whole new rig to drive them – new computer, new HD cards… new everything basically. I might have to break out the balaclava I think… it’s around here somewhere.