system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why do we have a whisper voice? Why can’t we just talk normally, but quiet?

When it’s quiet and you need to keep your voice down, you whisper. But a whisper isn’t just a quiet talk, it’s an airy, base-less sound. Why can’t we just talk normally, but quiet?
gpt
You can, we can vary the volume of our voice without changing the tone or pitch much. But there's a lower limit because it takes a certain amount of airflow to get our vocal chords vibrating at all...less air than that and you don't get any tone. It's like blowing really softly into a flute...you don't just get a really quiet note, you get nothing, there's a minimum loudness "to make the instrument work". 

If you want to be quieter than that, then you whisper, which is how we can talk without using our vocal chords.