"Active participation" means participating in the prayer of the Mass.
"Active participation" originally meant the congregation participating in the priest's sacrifice, especially by singing the Gregorian chant (cf. Pope St. Pius X, Tra le sollecitudini).
The words of consecration must not be said in a loud voice.
The Council of Trent, Session 22, Doctrina de ss. Missae sacrificio, 17 September 1562 anathematizes those who think
Canon IX.— […] that the rite of the Roman Church, according to which a part of the canon and the words of consecration are pronounced in a low tone [submissa voce], is to be condemned; or, that the mass ought to be celebrated in the vulgar tongue only
It also says (Chapter V. On the solemn ceremonies of the Sacrifice of the Mass.) that
holy Mother Church instituted certain rites, to wit, that certain things be pronounced in the mass in a low [summissa], and others in a louder [elatiore], tone [voce].
This teaching was also taught by Pope Pius VI in his bull Auctorem Fidei condemning the heretical Council of Pistoia [DZ 1533]:
The proposition of the [heretical] synod [of Pistoia:] […] "[…] by expressing it [the liturgy] in the vernacular language, by uttering it in a loud voice"; […]—rash, offensive to pious ears, insulting to the Church, favorable to the charges of heretics against it.