As well as the possibility of the computer not keeping up and missing little pieces, speed problems are as I often say usually a problem of one or more of the following:
- Mismatched sample rates somewhere between Audacity, Windows and the device
- Incorrect drivers for the device doing the playback and recording
- A different device is performing the playback to that doing the recording, and the clock speeds of the devices do not match (it is normal with consumer grade equipment that they would not match).
We have a FAQ ready made for this:
http://manual.audacityteam.org/o/man/faq_recording_troubleshooting.html#sync.
So in your case, have you got the correct latest Lexicon drivers from http://lexiconpro.com/en-US/softwares/lambda-driver-installer-vusb-drivers-v2-7-windows ? Note that the Lambda does not work on 64-bit XP, if that is what you have.
Also see Important information for Windows XP users about the potential risks of using XP.
Gale