I wanted to call this article: What’s wrong with USB?
1. Resolution. Yes, sample rate compatibility has nearly always lagged behind the steadfast 24/192 of most S/PDIF inputs. Even two years ago many a DAC’s USB input would only decode up to 48kHz sample rates. This is slowly improving. Some examples? Sure! The now ubiquitous XMOS chipset has seen Peachtree lift its iNova from 24/96 compatibility to the Nova125‘s 24/192. Ditto Emotiva: their XDA-1 maxed out at 24/48. Its successor – the XDA-2 – now runs up to 24/192. Curiously, it can’t do 176.4kHz. Neither can the recently reviewed Wadia 151PowerDAC Mini but I cut it greater slack as it was launched way back in 2010 when 48kHz USB was more the norm. The 176.4kHz sample rate hole is annoying if (like me) you happen to prefer 4x software up-sampling on Redbook material. If you’re in the market for a new DAC, scour specification sheets and reviews to ensure your shortlist models can handle 176.4kHz and 88.2kHz.
2. Sound. No, I’m not trolling. I’ve said it before and I’ll say it again: the sound from the USB input on nearly all DACs (that I’ve heard) falls short of its neighbouring S/PDIF input. That’s assuming the DAC can do both. I know this from regular and consistent deployment of USB-S/PDIF convertors. Manufacturer marketing departments are understandably coy about this USB performance shortfall. They’ll hit you with words like ‘asynchronous’ and ‘world class’ (what does the even mean?) and hope you’ll let your credit card fly. That’s business!
When you buy a DAC, buy a USB-S/PDIF convertor too. You’ll be grateful that you did. This kind of DAR reader email is not uncommon:
“John – I took your advice and bought a convertor to feed the DAC in my desktop system. (ATM it’s a Channel Islands VDAC from my main rig but I’m looking for a replacement). It’s only the Musical Fidelity V-Link 24/96, but the difference it has made is dramatic. Better imaging, far more relaxed and natural sound. Previously unpleasant-sounding discs now sound fine.
So many thanks – Bruce”
My experience with the likes of the Wyred4Sound’s uLINK and – more recently – Resonessence Labs’ Concero always sees me ultimately ignoring the DAC at hand’s USB socket in favour of its coaxial S/PDIF*. Not only do these devices re-clock data – less jitter for you – they also buffer the DAC from the electrically noisy computer. With a Concero or uLINK in the chain the DAC is no longer directly connected to the host computer; the DAC is (to some extent) protected from the computer’s EMI/RFI noise. Moreover, these convertor boxes open up all sample rate possibilities to 192kHz (with no 176.4kHz hole).
Resonessence Labs’ Concero is the first device to finally pull up alongside the previous budget champion from Philip Gruebel. The Concero’s sound is damper and smoother than the Audiophilleo2**. Moreover, the two in-built up-sampling algorithms in the Concero can be switched in from any Apple remote – the CPU-intensive 4x up-sampling can be externalised. Oh yeah – the Concero can also stand alone as a great-sounding DAC. How much? US$599.
* The Metrum Hex’s M2Tech OEM USB interface doesn’t take 5V from the host computer. It has its own internal power source. This is the only DAC I’ve heard to date whose USB sounds as good as the Concero feeding its S/PDIF.
** I’ve heard from several sources that the PurePower-modded Audiophilleo (AU$1099) is one of the best sounding USB ‘transports’ currently available.