What does it mean for a device to be 'plug-and-play' or 'class-compliant'?
A class-compliant device (also known as plug-and-play) is one that doesn't require extra drivers to connect your Windows or Macintosh computer, or to your iPad. These devices use drivers which are built into the host (i.e. the computer or the iPad) operating system.
To find out if your USB audio or MIDI device is class-compliant/plug-and-play, check the manufacturer's web page. If it connects automatically to any computer without requiring you to install drivers from a website or a disk, it is probably class-compliant/plug-and-play.
For some tips on troubleshooting class-compliant/plug-and-play device troubleshooting tips, refer to this article.