What's the difference between より and よりも?


I came across this sentence:

[code]

    光{ひかり}は音{おと}よりも速{はや}く進{すす}む
    
[/code]

And I don't understand the purpose of the word よりも. I have a feeling that より
and よりも have basically the same meaning (more than) and も is used to emphasis
it.

Is there any difference between より and よりも?

Thanks, Or

