It's not a literal silence, as I don't think the magic here is based on words. That reference is a relic from a time when it was suggested it was.
Judging by picture and name, I'd say it is is suggested that it silences sound though. Unless those notes are in fact a spell or something
Anyway, in the best world I created so far, magic is the art of 'giving orders to elements' where elements are powerful and sentient beings created by Gods to serve people. So, for example, fire is a sentient being, as well as earth below your feet is. The art of magic is the art of communicating with these beings, using your willpower and mental stamina (called mana
) to force them to do your bidding.
The problem though is that due to the specific nature of elements, communication with them ain't easy. For example the language of earth is the language of stability, resonance and resistance. To communicate with earth, you have to stand still like a stone, to cause an earthquake, you have to shake like the ground itself, to become hard as stone, you have to behave like a stone. You have to become one with the element you are trying to communicate with.
On the other hand, fire magi dance like flames, water magi move fluently and air magi let their bodies move with the air, so that they can become one with the element they are communicating with.
Speech or music might be used as a way to help you reach that state of union with the element, for example earth magi might use monotonous, repetitive words or sound to enter resonance with earth. Fire and air magi might use some music to help them 'dance' with their elements. Water magi prefer music resembling the sound of waves and flowing water. Stuff like that.
Generally, an apprentice might have problems using magic at all without speech/music, since it's much more natural to people than the more advanced techniques.
An experienced mage might be weakened by inability to speak or hear, but should be able to unite with his element nevertheless.
The most powerful magi can unite with their element at will, and silence wouldn't hurt them one bit. Well, that's not strange considering that at this point, they are 'thinking like their element' rather than 'thinking like humans or whatever their specie is'.
The funny thing is that to become a great white mage, you have to unite with the dragons, and to become a powerful black mage you have to unite with the forces of evil. So, it's quite impossible to use white magic and black magic at the same Time, while other elements can be joined together.
Though, that's not surprising, considering that those two elements are in fact good and evil, while the white(light) vs. black(darkness) is more like a convention, and there is nothing wrong with a white mage going around in black clothes
I personally prefer characters like a 'badass jedi dressed like Darth Maul' while 'evil dudes looking all bright and shiny' are lame