China N99i problem with out voice timbre

Hello, I have a problem. I have china N99i with MTK6225. Yestarday while I spoke suddenly people in opposit side say me that can not recognise my voice and can not understand me. I am traying on other phone and fix that my mobile send changed voice. My voice is with slowly speed and timbre has too many bass( low frecuency). Can you tell me what I can do. Please.

Nikolai