Supratek News has published an article about the exaU2I USB-I2S interface: Ultra Hi Resolution Digital
Thank you, Supratek
Here is an abbreviated version of the review:
Ultra Hi Resolution Digital
USB input dacs are becoming very common and are sounding very good, however in my experience , during the first half of 2011 the best results came from using a dedicated USB-SPDIF convertor, something like the M2Tech Evo or the Audiophilleo.
I have 4 of these devices, and i really like the Audiophilleo2 .
The USB-SPDIF conversion must be very critical as using these devices can even make an older pre 2011 dac sound very good, which indicates digital design has benefited more from this aspect than the actual dac chip design. My (oldish) Lavrey DA10 (with the Audiophilleo) working at it's limit with 96Khz sampling sounds much better than it does with straight spdif input and 44.1khz.
The Evo and a Teradac USB-SPDIF convertors also have an I2S output which in simplistic terms allows you to bypass the spdif receiver and input directly to the dac chip.
Should be a sizeable advantage, but I dont hear it that way, and prefer the Audiophilleo. The I2S cables have to be kept very short and I suspect there are impedance issues affecting performance, the spdif receiver is obviously there for a reason.
www.exadevices.com recently released a USB-I2S device with a max sampling rate of 384 Khz, which is pretty much state of the art (SOTA)
The device is the exaU2I and quote from website:
"exaU2I USB to I2S Interface
is designed for use in high-end DIY audio projects aiming to achieve sonic performance that rivals traditional audiophile grade gear. exaU2I is the first affordable device on the market that makes it possible to stream multichannel 384 kHz and 352.8 kHz DXD audio in full 32 bit resolution
from a PC to a DAC with professional mastering quality."
Sounds pretty good doesn't it, and so I imported the first one into Australia to use with a Twisted Audio Pear Buffalo 2 Dac which has provision for I2S input. The Buff uses the ESS Sabre dac chip and is 32 bit/192Khz so is a good match for the exaU2I.
But it didn't work, and it took quite a while to sort out. The Buff2 needed alternative firmware as it was optimised for spdif operation, fortunately TPA were able to make the required firmware and post it to Australia.
When i finally got everything connected up the first album I played was 192Khz sampled Peter Greens "Blue" using Windows 7/ASIO and JRiver Media Centre 16 player. First impression was "what is wrong" as I was hearing distortion - too my surprise I suddenly realized I was listening to the distortion of the guitarists amplifier, something I had missed on previous listens. On the next track he'd turned the overdrive off and the sound was clean, and so palpable. The most obvious thing is the complete lack of a digital sound , so much "air' and transperancy. The Audiophilleo is pretty good but this is at another level altogether.
Very, very accurate, there is nothing added, nothing taken away, you hear the recording exactly as it went on to the tape and came off the 192Khz ADC.(Provided of course it is a carefully and very well recorded and engineered recording, high sampling rates dont mean anything with bad recording techniques)
I think it is the best sound I have heard and is the type of sound I crave, but , and it is a big BUT, to hear this level of resolution you need accurate and highly resolving equipment, I find it peculiar that people say they cant hear the difference between 44.1Khz and 192Khz and then say they use SE amps and inadequately resolving speakers. You cant hear resolution if it is swamped by coloration.
And if you like "musical" , that is, you want to hear your interpretation of how the music should sound rather than an accurate reproduction , then something with the resolution of the exaU2I and Buff2 is not for you.
I revel in it - sure vinyl still sounds great and most of my music is in 44.1Khz ripped from CD , but JRiver and PureMusic for macs can upsample to 192Khz - it's not as good as a dedicated 192Khz recording , bit it sure sounds better than 16 bit/44.1Khz to me.
At the moment the exaU2I only works with Windows- I actually prefer to listen to my macmini for most listening, but until an Mac version is released (which could be even better) this will do nicely.
For those who are interested, the Buff2 has a number of analogue output options. It can be used in both voltage and current modes ,with discrete(or opamp) output, transformer outputs, tube output or can even be driven direct from the dac.
I tried all of these combinations and finally ended up using one of my very accurate tube preamps , off the SE ouput. The dac chip has SE and balanced outputs, but I actually prefered the SE ouput to balanced.
With a preamp on the output and driving into another preamp, gain is a little high, but gain = dynamics if used correctly . I'm currently building a fully balanced version of my tube preamp which will house the exaU2I and the new Buff3 when it is released . I wont be surprised if the SE version is better than balanced, but it will be switchable between SE and balanced.
This as as good as digital off a computer has sounded to me, and it must be SOTA , if not close to it.
Sure beats the hell out of any CD transport.