4 I am about to say what ye know. One who jubilates, utters not words, but it is a certain sound of joy without words: for it is the expression of a mind poured forth in joy, expressing, as far as it is able, the affection, but not compassing the feeling. A man rejoicing in his own exultation, after certain words which cannot be uttered or understood, bursts forth into sounds of exultation without words, so that it seems that he indeed does rejoice with his voice itself, but as if filled with excessive joy cannot express in words the subject of that joy....Those who are engaged at work in the fields are most given to jubilate; reapers, or vintagers, or those who gather any of the fruits of the earth, delighted with the abundant produce, and rejoicing in the very richness and exuberance of the soil, sing in exultation; and among the songs which they utter in words, they put in certain cries without words in the exultation of a rejoicing mind; and this is what is meant by jubilating....
Source: The Enarrations, or Expositions, on the Psalms (New Advent)