Berkeley Audio 的網站特別強調兩點:
1. 他們輸出段的電源是獨立的, 不是電腦來旳, 想當然爾。
http://www.berkeleyaudiodesign.com/alpha-usb/
Great care was taken in the design of the Alpha USB to isolate the noisy computer/USB environment from the digital audio output. The USB receiver and processing are powered by the computer, while the output master clocks and line drivers are powered by a separate isolated linear power supply. Two key factors combine to achieve the excellent audio performance of the Alpha USB - the unprecedented degree of electrical isolation between the USB input connection and the audio output and the very low noise/low jitter performance of the individually tested audio output master clocks
2. 他們的跟輸出之間有絶佳的雜訉隔離, 用的應該是先進的 isolation transformer, 在這個網頁中有介詔。
http://www.computeraudiophile.com/f6-dac-digital-analog-conversion/15-universal-serial-bus-industry-standard-cables-connectors-and-communications-protocols-between-computers-and-electronic-devices-spdif-converters-shootout-15327/
The 'dirty' and 'clean' sides are both isolated by a chip. The lettering on the chip was removed, but I’m pretty sure this is the ADuM* chip, isolating the I2S lines between the XMOS chip and the SPDIF output.
*The ADuM chips are digital isolators based on the Analog Devices, Inc., iCoupler® technology. Combining high speed CMOS and monolithic transformer technologies, these isolation components provide outstanding performance characteristics superior to alternatives, such as optocouplers.
我剛好有一台 REGA DAC 他們用的也是 isolation transformer,
http://www.rega.co.uk/dac-r-1.html
The USB input stage is comprised of a bit perfect XMOS USB Audio 2.0
with asynchronous clocking. The USB input stage feeds the Optical and
Coaxial input stage via an isolating transformer giving total isolation from
the host computer.
REGA 有不同的的 filters 可以選,這是在隔絕訉源雜訉之後在 Digital Domain 做的調整,照他們説聽感會不一樣, Stereophile review 有一些介紹
http://www.stereophile.com/content/rega-dac-da-processor-page-2