I am a computer-science student working on a signal processing project on smartphones based on recorded microphone signals. For my project, I need a really "reliable" recorded signal. The system works perfectly when I put phones on a table and don't touch it. However, when I touch the phone by my hands (e.g., press a button when phone is static in the table), the recorded data in microphone seems changed dynamically for unknown reason. For example, at certain time period, the received audio (sent from my laptop) is louder.
Since I am not an expert of electrical theory, I would like to know if there is any theory about this phenomenon (such as touching make the diaphragm hard to vibrate) I know the microphone is a MEMS microphone which operates as a condenser type microphone but not sure if there is any reason that the recorded signal changes depends on how user touch the microphone (or smartphone body).