how can i disable the high pass filter on the headset mic on the iphone 4?

i would like to use my iphone for recording and frequency measurement apps. i have an adapter that allows me to use the headset mic input https://www.petersontuners.com/index.cfm?category=135&action=itemView&itemID=39 however, there is a high pass filter up to about 200Hz on both the headset mic input and the external mic. one app apparently has a work around in ios6 http://blog.faberacoustical.com/2012/ios/iphone/finally-ios-6-kills-the-filter-o n-headset-and-mic-inputs/ but is there an iphone setting that could temporarily bypass the filter? if not in ios6, if i upgrade to ios7 will i be able to do this?