Sound card can only take 1V maximum so you will need a voltage divider. I don't think the sound card is synchronized with PC clock. In rare occasions the sound could even be off since the sound card crystal is no the same as the RTC crystal. I had this problem on one computer I used. The recording and playback time are different, especially when you record a long lecture of 50 minutes. The recording is per the sound card crystal but playback was somehow per the PC clock. I used every recording and playback software on that computer and other computers and came to the conclusion that the computer has a problem with sound card.