Dear Jay,

To add to Andrew's points (that I agree with); you won't need a DI if you would get a soundcard that supports balanced output. The main task of a DI box is to convert a unbalanced signal to a balanced on. Another factor is that laptop build in soundcards are made to be cheap and small. They do a decent job with system beeps and playing mp3's on the build in speakers but they aren't meant for presenting your detailed, lovingly crafted sounds and music over a multi Kilowatt PA system toa attentive audience, and how could they?

If you have a budget I'd go with a soundcard from a reputable brand featuring balanced outputs, preferably one that can use it's own power suply. If you do that humm will be a thing of the past (unless something, somewhere goes very wrong). In that case you'll likely have multiple outputs that you could mix on a hardware mixer; some people find that more direct and convenient and it will give you a chance to cut the sound in the envent of a system crash.

If there is no budget use a pair of DI boxes over a "Y" cable to the build in card and lift the ground of your laptop adapter (if it has one, some brands like Apple don't). Ground-lifting plugs cost less than a burger and more profesional clubs should have DI boxes. It won't sound as good but at least that strategy should make sure there is no humm either.

Hope that helps,
Kas.

2009/4/14 Andrew C. Smith <acsmith@willamette.edu>

I just did a couple of laptop performances, and having two DI boxes on
hand is extremely helpful. You can either use a Firewire interface or
a Y-plug from your headphone jack, but the DI box is important because
the snake that runs to the front of the stage is usually balanced XLR
only. I carry my own two DI boxes, because I want them to be
identical and sometimes the venue only has one box.