Around this time, Gregorian chant and plainsong began to be developed (11th-13th Century). These types of pieces were originally monophonic (having only one unaccompanied musical line). This was usually due to rules put forth by the Church that did not allow certain harmonies or rhythms. Overtime, the use of polyphony and harmony was used in these chants as they developed and evolved. The Church was still very much involved in how the music was written. Common instruments in this time period are: the flute, the recorder and the lute.
As Polyphony developed (14th-17th centuries) rhythmic notation was introduced. The fourteenth century ars nova (new art) style developed bolder harmonies, required wider vocal ranges and used more interesting rhythms (though bar lines would not be introduced until late in the sixteenth century). Though ever higher treble voices were needed, the Church could not resign itself to the use of female voices (proscribed in I Corinthians 14:34) and turned instead to the increased use of boys with unchanged voices (putti ).
But Boys suffered the drawback of having relatively brief useful careers after their protracted training, and the next step was to use mature males singing in the falsetto register. The fifteenth century saw the Council of Trent attempt to restore purity to the liturgy by outlawing the use of such elaborative material as tropes and SEQUENCES. It also saw important new activity in the creation of polyphonic Masses and MOTETS. As the developing contrapuntal style generated interest in the range and timbre differences of the lower male voices, the last primary voice-type term, baritone (Greek for 'weighty sound'), came into use.