Teenagers have a new ring tone that adults cannot hear, because the frequency is too high: 17 kHz.
Test it with Audacity:
File / New
Generate / Tone… Frequency: 17000
I cannot hear it. But I can hear a 14 kHz tone.
Analyzing the first one with Audacity (Analyze / Plot Spectrum) reveals a peak at 15 kHz.
Keep this in mind when testing:
- your hardware (sound card, speakers, …) must be able to handle the frequency (20 kHz is a common limit)
- when exporting as mp3, select the right sampling frequencies (Nyquist)