How do I enable and adjust A3D / 3D Sound?

There can be many reasons for stuttering problems in game, too high a rate, poor connection, too high detail for graphics. However the most common reason is your graphics card rendering ahead, this can be helped by setting the cvar r_finish to "1" and performing a vid_restart

seta r_finish "1"
vid_restart

If setting r_finish does not help read the information on the following guide pages:

Connection Tweaks
Framerate and Visual Tweaks