Why do peoples voices sound different when they are talking on the phone?One major reason for voices sounding different is that the frequency response of the telephone system is limited. The range of the human ear can extend right up 20kHz or more, especially in younger people. A connection over the telephone has a much narrower bandwidth, typically restricting the highest frequencies transmitted to a little over 3kHz in many cases.
That's adequate to convey intelligible speech, but naturally it changes the sound of the voice subtly by filtering out the highest-pitched components. It's the same sort of effect as you would get by listening to your favorite record on A.M. radio versus listening to it on F.M. or from a CD.
The telephone also reduces frequencies at the very lowest end of the audible range as well.
Hope it Helps!!!