Does an external soundcard interface add noise?

This month, there's an interesting, brief article in the RSGB's RadCom about receiving datamodes by connecting a transceiver to a PC instead of using an external soundcard. 

The rationale behind the idea is that an external soundcard can add noise to the listening system - something we all strive to reduce so far as we can.  

This article coincided with my doing quite a lot of receiving recently.  I rememered that last year, I bought two USB surround sound dongles that has both headphone and microphone sockets.  I wondered if this might allow me to hear WSPR via the rig's headphone socket to the dongle's microphone input.

It did!

The sound levels are a bit strange, but once the correct volume is found, the reception sensitivity seems either the same as or better than the external ZLP Electronics interface that I have.  In fairness to ZLP, that external interface does seem to introduce very little, if any noise, and is marketed as such.

I heard DP0GVN quite strongly this morning with the more direct interface.  I didn't hear him at all with the ZLP box yesterday morning, but that is more likely to be a propagation thing, I guess.

Not exactly earth-shattering, but an useful thing to know, especially when the dongles only cost about £2 each, direct from China!