Unless I’m mistaken though, a High Mass and a Solemn High Mass are the same thing.
The confusion arises from there being a disparity between the official terminology of the Church, and the common phraseology employe in English-speaking countires, especially the USA.
The 1962 rubrics distinguish three different “levels” of Masses.
There is the
Missa Solemnis, which is a sung Liturgy with priest, deacon, and subdeacon. This is the normative celebration for every liturgy, though by no means the most common.
Then there is the
Missa Privata, which is a spoken liturgy, celebrtaed by priest alone. I believe the word privata is meant in the sense of “deprived”; that is, of the external ceremonials of the
Missa Solemnis.
A
Missa Cantata is a liturgy that is sung, but celebrated by priest alone. It’s a sort of compromise between the
Missa Solemnis and
Missa Privata.
In some places, it was customary to refer to the
Missa Solemnis as “High Mass,” the
Missa Privata as “Low Mass,” and the
Missa Cantata as “Sung Mass.”
Among others, though, it became common to refer to the
Missa Solemnis as “Solemn High Mass,” the
Missa Privata as “Low Mass,” and the
Missa Cantata as “High Mass.”
So it depends on who you talk to.