The PDI-01 D.I. box is a passive unit that works exceptionally
well in almost any standard application. A specially designed
high quality balancing transformer provides smooth frequency
response throughout the audio range, huge amounts of headroom,
and maintains signal integrity. A rugged diecast alloy
box provides excellent RF shielding.
The SOFT GND feature is new and exclusive to the latest
version of the PDI-01.
The two grounds are not directly connected to each other, but instead are
connected through a capacitor to form a "soft" ground. The reason
this "soft" ground is that many computers and other equipment radiate
frequencies that have a very disturbing effect on the signal, which can be
heard as a high-pitched buzzing sound. This can be eliminated by grounding
through a capacitor, which, due to an adequately high resistance, also takes
care if the normal 50/60Hz AC hum. The SOFT GND should be used if the PDI-01
is connected to a computer sound card or interface device.