system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why do songs sometimes sound at a different pitch when the volume is low?

This can happen even with very famous songs, or songs that you know very well. As a musician, I feel confident to know the pitch of those songs I know well yet when the volume is too low I can’t make out the exact pitch for 1-2 minutes.
gpt
Something harmonically important is not loud enough to establish the tonal center. Likely the bass. Without the bass notes (the chord roots), the tonal center can easily become ambiguous. Sometimes the remaining musical parts, such as guitar, piano, melody, etc., can still define the key and tonal center, but often in pop music, a lack of strong harmonic instruments isn't always present.