Some modern desktop computers now feature sound built-in to the motherboards.  In my experience, built-in sound systems are not quite as good as separate sound cards.  I believe that this is because built-in sound systems experience more electrical noise which impacts the quality the input.

One particularly known bad case is with Dell Dimension desktop systems.  In my experience, there is something wrong with the built-in sound in it Dell Dimension desktop computer.  When you use Dragon NaturallySpeaking on such a machine, you experience the classic symptoms of the bad sound card: higher than usual error rates and, most noticeably, a significant speed degradation.

Having used Dragon NaturallySpeaking on a number of different systems, I feel qualified to diagnose the Dell Dimension computer as having some type of problem in its built-in sound system which interferes with speed recognition.  If you have a Dell, that are recommend to purchase a separate sound card.

(This text is actually being written on a Dell Dimension XPS P200s system, but in order to get Dragon NaturallySpeaking to work reasonably, I had to disable the built-in sound system on the motherboard, and use a separate sound card instead.)  (Ensonic Soundscape VIVO PnP if you are really interested.)