Precisely Adjust Volume Levels on your Mac
You can precisely adjust the volume levels on a Mac by holding down the Shift+Option keys while pressing the Volume Up/Down keys. This lets you adjust the sound level by 1/4 of each notch (as opposed to a full notch).
This is perfect if you like to precisely adjust the audio level of speakers, though it’s used best with external speakers which tend to play either too soft or too loud. Easily the best way to find the best volume for you.

Is there a way to change that you have without pressing the Shift+Option
key the volume at that way?
That’s pretty neat. So I started playing with it a bit on my MB and found that holding shift mutes the sound it makes when adjusting the volume, and holding just option will open the sound system prefs. Which then lead me to find that you can hold option and press the expose, dashboard, keyboard (if you have the illuminated keyboard) and brightness options.
Hey, the trick works when setting screen brightness too!
But on the screen brightness is no using because it only changes at every 4th frame
wow. this is awesome. I have been so wanting something like this. thank you
[...] You can do the same type of precise adjustments when changing your Mac volume levels. [...]
i just recived a used Mac from my cousin, however i have only worked with Windows my whole life. There for i am useing a keyboard with numberlock ect. and i dont know how to change the volume. help?
you can adjust the sound volume using the menubar too, the icon looks like a speaker with sound coming out of it.
Otherwise you can just navigate to Apple menu -> System Preferences -> Sound and adjust the ‘Sound output’ level to whatever you desire.
Is there a terminal command to make this default?
This feature is not available on Lion (and presumably Mountain Lion).
RIP
It IS available in Lion 10.7.4 (I have not tested in any other versions):
Shift+Option+Volume or
Shift+Option+Brightness
Adjusts those settings in smaller notches.