-- The fadetime in seconds
property fadetime : 3

-- The target Volume of the fade 0-100
property targetVolume : 0

-- Pause the player when the fade is done true/false
property stopWhenDone : false

-----------------------------------------------------------------------------

tell application "Spotify"

    set deltaVolume to targetVolume - sound volume

    if deltaVolume is not equal to 0 then

        -- calculate the time for each step to end
        set steptime to fadetime / deltaVolume

        -- inc/dec step size
        set step to 1

        -- if it is a decrease in volume
        if deltaVolume < 0 then
            set steptime to -steptime
            set step to -step
        end if

        -- Do the fade
        repeat with v from sound volume to targetVolume by step
            set sound volume to v
            delay steptime
        end repeat

    end if

    -- optional stop
    if stopWhenDone then pause

end tell