Sorry, jargon. The eucharistic prayer, the core of the mass, is the canon. Technically it was never silent but in the old rite the priest said it in a barely audible mutter facing the altar - in a high mass there would be lots of music going on at the same time.

The reason why this was a Thing at Trent is complex but boils down to whether you think it matters for the efficacy of the mass that it is entirely heard - and comprehended - by the congregation.