> So the phone company can compress and send a lot more data
Actually, the limits date back to analog phone lines with circuit switching of a century ago. Back then there was a wire going through switches from one phone to another.
The quality requirements were that those lines had to pass 300 Hz to 3.4 kHz or so. That often required "pupinization" - adding inductive coils to tune the line's frequency response.
If you look at a spectrogram of your voice, there's very little power above 1.5 or 2 kHz. However, it seems the high frequency part is important to understandability, including perception of emotional overtones.
(Just the other day, playing with modems, we found a weird case - voice being pumped through before the call was considered completed - which I suspect is the persistence in digital protocols of the analog behavior of a century ago.)
Actually, the limits date back to analog phone lines with circuit switching of a century ago. Back then there was a wire going through switches from one phone to another. The quality requirements were that those lines had to pass 300 Hz to 3.4 kHz or so. That often required "pupinization" - adding inductive coils to tune the line's frequency response.
If you look at a spectrogram of your voice, there's very little power above 1.5 or 2 kHz. However, it seems the high frequency part is important to understandability, including perception of emotional overtones.
(Just the other day, playing with modems, we found a weird case - voice being pumped through before the call was considered completed - which I suspect is the persistence in digital protocols of the analog behavior of a century ago.)