I'm trying to compare two audio samples of speech from two different Android smartphones to determine if the people are co-located. I'm doing this using the frequency bins of an FFT between 300 Hz - 3400 Hz. When the two devices are sitting on a table, I have good results.
However, when the devices are placed within pockets, the audio is recorded differently than when they are placed on a table.
Does anyone know exactly what happens to the audio frequencies/signal when the microphones are covered by a pocket or a bag? Are certain frequencies filtered?