How to disable audio output processing on an htc phone with Android

How to disable audio output processing on an htc phone with Android

I am trying to measure the audio path from speaker to microphone on two
different phones, an htc Wildfire S running Android 2.3.5, and an htc One
X running Android 4.0.3. Using Eclipse, I coded an app that has wave files
played back using an android.media.MediaPlayer. However, my recordings
show that something like an automatic gain control is applied to the
output, as loud files are attenuated, and the recordings feature almost
equal amplitudes, although the played back files vary widely in their
respective amplitudes.
How can I switch any processing of the audio data off prior to output? I
would like to obtain direct control over raw audio output.
Thanks in advance.