Francisco Guerrero became the most influential and respected composer in Spain in the time of Philip II. Trained first by his brother and then tutored by Cristóbal de Morales he was a versatile and gifted musician who not only sang and composed but was an excellent player of the organ, vihuela, harp and cornett. Stylistically he's somewhere between de Morales and de Victoria not as dour as Morales and not as concise (or cheerful) as de Victoria. His setting of the Vespers hymn O lux beata Trinitas (O light, O blessed Trinity) is written in the 'more hispano' —'in the Spanish manner' and so it's not plainchant as such because it was notated mensurally, in other words it was meant to be performed using various note values or even even in strict metrical rhythms. It's in duple time and if you listen carefully you can hear the top voice paraphrasing the chant. Enjoy :-).