Exactly what it says on the tin.
I have a Sound Blaster X-Fi Xtreme Audio Notebook sound card and I was measuring its output frequency using frequency counter connected to the card's output. Frequency was generated using a program called FrequencyGenerator. I've noticed that it can't provide frequencies higher than 16 kHz (upper limit of audible range is at 20 kHz) and I found that strange.
Is there any info on common maximum frequencies provided by sound cards? I know that for example Realtek ALC 268 can provide as much as 19500 Hz (which is pretty close to the needed 20 kHz), but since X-Fi is supposed to be better than average integrated sound card, is are ALC 268's capabilities an exception or is the X-Fi just really bad card (as in has low output spectrum)?