There are lots of interfaces out there that will do what you want. What he said ^^^ about mixer. If you're just looking to take four sources to four
tracks, you don't need one. I have a Tascam
US600. It does exactly that and works great. Four mic/line inputs with preamps to four inputs in computer by USB. Input 1 doubles as a Hi-Z instrument input if you plug an instrument cable in instead of a mic cable. There's also a stereo SPDIF input so if you have a device with SPDIF out that could be two more inputs. I don't use that. It has an onboard headphone driver with local monitoring. You can set total headphone volume and mix of signal from computer and the signal from you inputs, so you can listen to what you are playing while you play along with previously recorded tracks or other content from the computer. Also has midi in and out.
IF you are looking to record more than 4 sources at the same time, but want to record them down to four channels, you might want a mixer. I don't know of a mixer with four outs to USB, but I'm sure they're out there. I use a Behringer Xenyx1204 and run it to two of the Tascam US600. Gives me up to 12 inputs that mix down to two channels plus the other two separate channels. Works really well for not much $. I wish I could find an inexpensive
preamp or mixer with SPDIF out. That would let me record six tracks simultaneously!
Behringer Xenyx1204 + Tascam US600.
Hope this helps,
J
