low frequencies cut when using headset input

When I record audio tracks in garageband, the low frequencies are cutoff, so the bass guitar and kick drum are very weak.

I am using the analog headset line input to my ipad1 and iphone 5 by using a kvconnection cable : http://www.kvconnection.com/product-p/km-iphone-2trs-a22.htm?CartID=1

The cable seems to work fine, as it forces the iOS device to select the line input instead of the internal microphone, and gets rid of the repeated popping noise I was getting before when using a direct cable without the built-in attenuator.

The folks at kvconnection were very helpful and pointed me to this very informative article http://blog.faberacoustical.com/2012/ios/iphone/finally-ios-6-kills-the-filter-o n-headset-and-mic-inputs/ which explains that there is a high-pass filter applied. But in iOS6, this filter can be bypassed.

Is there a way to bypass this filter in the garageband app, or are there any other audio recording apps that can bypass the filter? Apparently the SoundMeter app does this by using "measurement mode". I tested this on my iphone 5 with the latest iOS6 and it still has the same issue.