Maybe you've never heard of him, but he was a great 20th century Polish composer. We sang his "Agnus Dei" in Concert Choir my freshman year of college, back in 1986. It's a stunning piece, full of drama and pathos. Here's a gorgeous performance by the Warsaw Philharmonic Choir.
There's a sort of notated shriek at 4:50 - - Penderecki made a chord using ten pitches out of the readily available twelve, split the choir into something insane like twenty parts, and put most of the parts high in their voice range. It's something to hear, and even more intense when you're in the middle of that sound.
We had one rehearsal where we sang the long build-up to that moment and we gave our all when we came to that gruesome chord. Our conductor, the extraordinary Robert Fountain, stopped the rehearsal, thought it over for a moment, looked at the score, and said, "I could use a little more E natural from the baritones."