How to measure a dc or ac signal using PC as oscilloscope?
There are differences, you can't get DC into a sound card as everybody is telling you. Hopefully you can see the differences here. 
Oscilloscope probes also have a much better bandwidth than a 3.5mm cable. The oscilloscope also has an "amplifier" to gain the signal.







simulate this circuit &ndash; Schematic created using CircuitLab