I am looking at getting a cheap USB soundcard dongle, and it has only 2 ports, microphone-in, and audio-out. It has no line-in. I know that microphone ports have a DC voltage (from what I remember when I had another soundcard in another computer, this was about 2V, this is NOT 40V phantom power) coupled onto the signal line with a pull-up resistor on the sourd-board itself, designed to power an electret microphone. When I buy this USB soundcard dongle, I really don't want to actually cut a tracing on the board to disable the DC offset on the microphone signal line, as I will want to be able to use it for both a mic and an un-powered audio source (depending on what I need at any given moment). Therefore, I much rather have a DC-blocking audio cable. I know I can make one with either an RC highpass filter, or using a 1-to-1 isolation transformer. I actually made one once, a long time ago for a different soundcard I had in a different computer that I'd had at the time, but I don't remember where I put it, so I think it's lost for now. Also it wasn't exactly professional-manufactured quality. The soldered connections on the audio isolation transformer were covered over with electrical tape, clearly something that somebody just hacked together.
I want to buy (if one exists) a professionally made DC-blocking audio cable, designed with the intent of basically turning a mic-in port into a line-in port, so that non-powered audio sources can get their audio signal into a soundcard via its mic-in port. Ideally the cable will contain the isolation transformer or the RC lowpass filter directly in part of the cable itself (such as an end connector, or a tiny box in the middle of the cable that's professionally molded into the cable itself so it's not an obvious added-on part).
And one more question, not specifically related to the main topic of this thread. The 2 possible low-price USB soundcard dongles I'm considering are these:
This one from Sabrent
https://www.amazon.com/Sabrent-External-Adapter-Windows-AU-MMSA/dp/B00IRVQ0F8/This one from Plugable
https://www.amazon.com/Plugable-Headphone-Microphone-Aluminum-Compatible/dp/B00NMXY2MO/I don't know which is better though. I've heard of Sabrent before, but I don't remember if it was in the context of being a good quality manufacturer. or in the context of it being a maker of cheap Chinese junk. I've never heard of Plugable at all though, and it sounds so generic of a name that it makes me think they might be some Chinese company that just makes junk that would break if you so much as sneezed. So does anybody here know which is actually the better brand?