Sound card makers focused on improving playback quality for music and games. As you speak, your voice generates electrical impulses in the microphone. The sound card converts these impulses into numbers that your speech recognition software can analyze. Good sound cards faithfully measure the electrical changes your voice generates. Bad sound cards introduce static and interference, making it difficult or impossible for your program to accurately determine what you said.
Most sound cards work fine for speech recognition.
In these systems, the sound circuitry is built in as part of the motherboard, the main computer circuit board which holds the processor. Many computer makers use this type of sound system. While this saves money for computer manufacturers, the sound wiring is physically closer to other circuitry and thus more likely to allow electric interference to degrade the quality of the speech signal. For best results, ask your vendor to install a separate, non-integrated card. USB microphones process the sound signal directly in the mic and don't route your voice through the sound card.