Mark - you mentioned that you had a sample rate of 19,200. That’s a very odd value. Try changing it to 44,100 (or 48,000) as you’ll get much better results. One possible manifestation of this playback line issue is if some other application is changing the soundcard’s sample rate. So check to see if you have any other software that might grab the soundcard running, eg screen/sound capture applications, Skype, etc