Constant volume for music on ios

Hello SteveShapiro,

Thanks for reaching out in Apple Support Communities. We understand that you're having trouble with your iPad's volume. It looks like some songs are too loud and some are quieter. We'll do our best to help. The songs that you're having issues with were they downloaded from iTunes or do you subscribe to Apple Music? This can help us to narrow down the cause of this issue. Do you continue to experience this issue after restarting your iPad? A restart can help to refresh the OS and connections.

Check out the following support articles:

Music Support

Restart your iPad

Adjust the volume on iPad

Cheers!

Not sure, but to my knowledge that option is not available on iOS devices.

Mp3 files might have different "normalizing" threshold, therefore their output sound pressure (dB) can be different.