I just got my Iconia W510 yesterday and noticed that when I tried to record sound either with the video camera or Sound Recorder that the volume was extremely low. I set the volume up to 100% in Control Panel but the problem still persisted. Then I noticed that if I had my external speakers plugged into the speaker jack the microphone worked fine - the volume was good - but if I pulled the speaker jack out the volume was horrible again.
I finally called tech support and he had me go into Device Manager and uninstall the two drivers that showed up under Sound - Intel SST Audio Device and Realtek I2S Audio Codec - and then reboot the system so that Windows would reinstall the drivers. This fixed the problem. Posting this here in case anyone else has the problem.