ExaSound Audio Design is a Canadian company that designs and domestically manufactures two DACs: an e18 multichannel model and the recently released $2499 two- channel e20, the subject of this review. So just what distinguishes the e20 from the veritable flood of new DACs showing up on the market these days? In my view, the e20’s most distinctive feature is its ability to play Direct Stream Digital (DSD) files in their native format without converting them to PCM data first.
That’s a new capability recently developed by industry heavyweights dCS, Playback Designs, and Channel D to handle the DSD format. If you’re unfamiliar with DSD recording, it was the system originally designed to record music for SACDs. SACDs don’t use raw DSD files; they add a copy-protection scheme that’s been difficult, though not impossible, to crack. If you’re unfamiliar with DSD files, they usually come with file name extensions of .DSF or .DFF. For example, a DSD file could be named “Bolero.DFF.” The e20 doesn’t just play standard 2.82MHz DSD files; it also plays the 5.64MHz double- speed DSD files, which some recorders are capable of making.
“And why,” you may ask, “should I care about playing back DSD files? Do they really sound any better than 192kHz/24- bit PCM files?” They should, since DSD DACs don’t have to use the very complex oversampling digital filter needed for PCM conversion. Although DSD DACs do use a filter, it’s very simple, not the sonically damaging brickwall filter needed for PCM. Another important question to ask if you’re considering a DSD-capable DAC is: “Are there any DSD files commercially available to play?” And the answer, at least as of Winter 2012, is not many. I don’t have a complete list of sources for DSD files; two that I’ve encountered are Channel Classics (channelclassics. com) and Blue Coast Records (bluecoastrecords.com). Both sources charge higher prices for DSD files than for high- resolution PCM files, but that’s hardly surprising, since it always costs more to pursue the bleeding edge of technology. If the demand for DSD files continues to increase, competition among record companies is bound to drive prices down.
The e20 also plays Digital eXtreme Definition (DXD) files, which are 352.8kHz/24-bit PCM files used in professional recording studios. DXD files are also hard to find, but a few are available from highresaudio.com. ExaSound’s Web site includes a page dedicated to DXD files from highresaudio.
For the hardware junkies, inside the e20 is an ES9018 Sabre32 DAC chip from ESS Technologies, which accepts up to 384/32 PCM files. As I just noted, there aren’t currently many companies selling files that advanced, but at least you can consider this capability as a sort of future-proofing. Software upsampling to 384kHz is also possible. Three precision oscillators are used to minimize jitter, with a claimed ultra-low 0.13 picosecond master-clock error. Eleven power-filtering stages are used to reduce noise, jitter, and channel crosstalk. The 128dB signal-to-noise ratio illustrates how effective these measures are.
Like most modern DACs, the e20 uses an asynchronous USB interface to minimize jitter. The USB receiver is galvanically isolated from the DAC circuits to eliminate noise or ground loops from your computer. The e20 supports automatic sample- rate switching if your source does. There are custom Audio Stream Input/Output (ASIO) drivers for Windows and high- performance Macintosh OSX drivers, which support PCM at sampling rates up to 32bit/384kHz and DSD at 2.82 or 5.64MHz.
As a frequent headphone listener, I was tickled to see that the e20 had a headphone output jack. ExaSound’s Web site claims the e20’s headphone amplifier is “capable of driving the most demanding headphones.” With an output impedance of only 1 ohm, the e20 should be able to drive low-impedance headphones like those from Grado. Unlike some headphone amps, the line output is not muted when you plug in headphones. The volume control on the e20’s front panel controls both headphone level and line level.