A rude example for converter nonlinearity , and history has seen the strangest kinds of distortions. But most times this is not the case, because even if sampling frequencies of both soundcard and external device are nominally 44.1KHz, they aren t synchronised. In professional multichannel audio and in '80s equipment a master which clocks all devices is present, but using resampling each device can function indepently from another, so most consumer soundcards with digital inputs use it. Non-rational resampling introduces a time delay, and also PLLs and other digital stuff can introduce time delays. Most analogue electronics have a delay of less than 100ys, the amount depends on its low-pass behavoir.
Time delay can cause phase interference .
More signal processing stuff . A converters simply with the wave s sampling frequency and cut off all noise above 10KHz with an analogue lowpass. BNC Ethernet is another example for this mode, while Twisted Pair Ethernet can really transmit and receive at the same time, not only virtually but in hardware. In analogue telephone lines, duplex means both directions, e.g. by using a circuit which substracts the own transmitter signal from the received signal so that only the words of the alien party are heard. Half-duplex in audio means most of the times that sampling rates of in and out must be the same.