I bought this biography Mompou by the Spanish poet Clara Janés. She knew Mompou who was friend of her father's, and he set poems of hers (and of her father's) to music. She reproduces some type-written pages from Mompou's writing about expressivity in music.
NOTA RETRASSADA -- NOTA RETINGUDA
NOTA RETRASSADA I RETINGUDA
Tota nota sensible, porta aquest dos moviments al mateix tempo.
Ser nota retrassada, nota retinguda, ó nota retrassada i retinguda, vol dir: que en uns casos domina el retraso, en altres el retingut i altres que la nota sensible necessita tant de l'un com de l'altre.
1. Tota nota porta el moment de retrás més o menys pronunciat segóns el valor de sensibilitat.
II. Tota nota retinguda porta avans del moviment, un retrás d'origen.
Es pot dir que la nota sensible és de origen retrassada.
[Every sensitive note carries those two movements at the same. To be a delayed note, or a held note, o a note delayed and retained mean: that in some cases the delay dominates, in other the holding and in other cases the sensitive note needs both things equally. Better: I. every note carries the moment of delay more more less pronounced according to the value of sensitivity. II. Every retained note carries before the movement of retention, a delay in origin. It could be said that the sensitive note has a delayed origin].
This is quite extraordinary, since it tell us exactly how to play his "Música callada." Delaying a note, playing it later than expected, and holding it for longer, letting it die out slowly, become part of the same continuum of sound. Whether I can achieve that or not, I at least know the direction to take. There are more technical details about notation that he explores too. He is tired of the Italianate language of musical indications. He makes the point that the purpose of phrasal lines is not to link notes together, but to indicate where the breath should come. They are not really "lligats" then but "deslligats."
The Catalan is extraordinary too. I feel that the Catalan conveys that emotion better than the exact translation into English or Spanish. "Retinguda" has a better feel that "retenida" would.