AppleScript System Events Volume Help

Here's some code that should help you. It uses the "get volume settings" command to get the current volume and "set volume" to set it (more information about these commands can be found in the StandardAdditions dictionary). The system uses a scale of 1..100 for volume settings, so the script converts it to a scale from 1..16 before adjusting the settings (as this scale is used when using the volume keys).

Code:

--Get the current output volume (on a scale from 1 to 100) and convert it to a scale from 1 to 16 as seen when using the volume keys
set currentVolume to output volume of (get volume settings)
set scaledVolume to round (currentVolume / (100 / 16))

--Use this code to increase the volume by a certain interval
set soundInterval to 1
set scaledVolume to scaledVolume + soundInterval
if (scaledVolume > 16) then
	set scaledVolume to 16
end if

--OR use this code to decrease the output volume by 1
set scaledVolume to scaledVolume - 1
if (scaledVolume < 0) then
	set scaledVolume to 0
end if

--After using one of the above, the volume needs to be set to the new level (before which we must convert it back to the 1..100 scale)
set newVolume to round (scaledVolume / 16 * 100)
set volume output volume newVolume