I forgot about this. There are several Sigmatel audio drivers compatible with the 1520. Currently it is shipping with the R167846, but the one reported to make the mic array work best is
Sigmatel audio driver R157031
Forum member sportscar wrote this about how to install if you have a different driver:
"You must first completely remove the original drivers from your system [ by right clicking ]. Windows will then install a "generic" driver when you reboot. After this basic generic driver is installed (which will not work either), install the R157031."
This is also supposed to fix the low mic level.