Plug the synth and/or drum machine into a mixer or audio interface of some sort via RCA (red and white, like into your TV) and then plug the interface via USB (or even better, firewire).
If you want a microphone then get that to. There's lots around so do your own research, read reviews etc...
Hey guys,
I've got a Dell desktop and a Dell laptop, and I've got them both running into my mixer via 1/8" to RCA, and they both have a strange sound. It's like a siren (low to high pitch, back to low etc.) but more crackly.
What is this sound and how do I get rid of it? It doesn't happen when...