Any experience w/ Ipod apps for spectrum analyzer?

I am looking for anyone who has experience with using their Ipod touch to adjust frequency levels in their theater.
I have the Shack SPL meter for overall levels. I am looking to tweak out peaks and valleys for each speaker, through my external EQ between my B&K preamp and Anthem amp.
I am wondering if any apps may BOTH produce frequency sweeps / test tones AND view the results. Do you use the internal mic or an external mic.
Thanks.