Taken from the Nano Manual which is available here:
http://manuals.info.apple.com/en/iPodnano_3rd_gen_FeaturesGuide.pdf
Setting the Maximum Volume Limit
You can choose to set a limit for the maximum volume on iPod nano and assign a
combination to prevent the setting from being changed.
To set the maximum volume limit for iPod nano:
1 Choose Settings > Volume Limit.
The volume control shows the current volume.
2 Use the Click Wheel to select the maximum volume limit.
You can press Play to hear the currently selected song play while you select the
maximum volume limit.
3 Press Play/Pause to set the maximum volume limit.
A triangle on the volume bar indicates the maximum volume limit.
4 Press the Menu button to accept the maximum volume limit without requiring a
combination to change it. Or, on the Enter Combination screen, set a combination to
require that the combination be entered to change the maximum volume limit.
5 To enter a combination:
 Use the Click Wheel to select a number for the first position. Press the Center button
to confirm your choice and move to the next position.
 Use the same method to set the remaining numbers of the combination. You can use
the Next/Fast-forward button to move to the next position and the Previous/Rewind
button to move to the previous position. Press the Center button in the final position
to confirm the entire combination.
Note: The volume of songs and other audio may vary depending on how the audio
was recorded or encoded. See “Setting Songs to Play at the Same Volume Level” on
page 30 for information about how to set a relative volume level in iTunes and on
iPod nano. Volume level may also vary if you use different earphones or headphones.
With the exception of the iPod Radio Remote, accessories that connect through the
iPod Dock Connector don’t support volume limits.
If you set a combination, you must enter it before you can change or remove the
maximum volume limit.
To change the maximum volume limit:
1 Choose Settings > Volume Limit.
2 If you set a combination, enter it by using the Click Wheel to select the numbers and
pressing the Center button to confirm them.
3 Use the Click Wheel to change the maximum volume limit.
4 Press the Play/Pause button to accept the change.
To remove the maximum volume limit:
1 If you’re currently listening to iPod nano, press Pause.
2 Choose Settings > Volume Limit.
3 If you set a combination, enter it by using the Click Wheel to select the numbers and
pressing the Center button to confirm them.
4 Use the Click Wheel to move the volume limit to the maximum level on the volume bar.
This removes any restriction on volume.
5 Press the Play/Pause button to accept the change.
Note: If you forget the combination, you can restore iPod nano. See “Updating and
Restoring iPod Software” on page 61 for more information.
Setting Songs to Play at the Same Volume Level
iTunes can automatically adjust the volume of songs, so they play at the same relative
volume level. You can set iPod nano to use the iTunes volume settings.
To set iTunes to play songs at the same sound level:
1 In iTunes, choose iTunes > Preferences if you’re using a Mac, or choose
Edit > Preferences if you’re using a Windows PC.
2 Click Playback and select Sound Check, and then click OK.
To set iPod nano to use the iTunes volume settings:
m Choose Settings and set Sound Check to On.
If you haven’t activated Sound Check in iTunes, setting it on iPod nano has no effect.
Hope it helps.
