I have been trying to choose some common spectral analysis software to analyze audio sources and wanted to have the ubiquity and portability that an iPhone / iPad offer, so I got "Spectrum Analyzer - Real Time Sound Frequency Analyzer" by ONYX.
 

 
However, even with a remote mic such as on the iPod earphone inline remote, I can tell that the internal mic of the iPod is still active, as I get large jumps in the display when I rub my finger against the bottom of the case, where the microphone sits inside.
 
I have tried disabling the mic in "Settings," but that also turns off the microphone that is coming into the jack.
 
Anyone find a way to restrict either this or some other spectral analyzer app to using the external microphone plugged into the jack only?  It would sure seem freaky if any time we are using our in line headphone mic for phone calls, that the internal mic is also operating and perhaps picking up the scratching of the inside of our pocket where the iPhone sits.
 
Also, do you know of a spectrum analyzer app that 1) stores the spectrum, and 2) supports the subtraction or some other method (e.g., integration of differences across frequency) of determining the match between two spectra?
 
Thanks!

Sound Analyser from myProject software will do what you wish if it is on the Mac side. I use it on Android.