low frequencies cut when using headset input

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

I am using the analog headset line input to my 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.

anyone else out there trying to record audio in GarageBand on iphone or ipad using the line input and having the same issue - low frequencies are dropped?

Apple, please put this in an update to GarageBand soon. This would make it the perfect recording app for iOS. It should be a simple switch to utilize the "measurement mode" that was made available in iOS 6 and bypass the low-cut filter.

Without this feature, you are forced to use a digital input to the 30-pin or lighting connector. Which does probably have better quality, but I have a mix of people and devices, some have the 30-pin, some have lightning. And the iPhones don't support the camera connection kit to plugin a USB device. And I really like being able to plugin a simple cable vs having a bunch of dongles.