Sound Check, EQ, and volume limit settings
Turn Sound Check on or off. Go to Settings > Music > Sound Check. Sound Check
normalizes the volume level of your audio.
Choose an equalization (EQ) setting. Go to Settings > Music > EQ. EQ settings
generally apply only to music played from the Music app, but they affect all sound
output.
Set a volume limit. Go to Settings > Music > Volume Limit.
Note: To prevent changes to the volume limit, go to Settings > General > Restrictions >
Volume Limit, then tap Donʼt Allow Changes.