USB is always bi-directional (works both ways). USB defines host and device or in terms of direction upstream (communications from device to host) and downstream (communication from host to device).
The host is always on the upstream side and has a type A socket (or OTG cable) the device is always downstream and originally devices were all supposed to be fitted with type B sockets or a type A plug (memorystick etc.). A host (mostly a PC, or android with an OTG cable) is the controlling device and an ADC or DAC is a device.
Example: iPurifier 3 plugs into the type B socket on an ADC device and the cable from the computer plugs into the iPurifier 3, exactly as would be the case with a DAC.
As long as the iPurifier 3 plugs into a “B” type socket (or via an adapter into a “A” plug – e.g. iDSD micro) it works in the right “direction”.
