Four part harmony is a term used to refer to music that has been written for four voices or four instruments. Each voice or instrument sings a different note which blends together to create music based on changing chords. The first voice, or first instrument, often has the melody, and each additional member of the chorus or quartet provides harmony and counter-melody with their parts.
The vocal parts that comprise four part harmony are soprano, alto, tenor, and base. Soprano and alto parts are typically sung by women, while men perform the tenor and base portions of the music. Each voice sings a different note of the supporting chords of the music while one voice carries the melody. Some sections of the music may also be written in unison, but the majority of the notes will be different.
Though this type of grouping may be used for many traditional harmonies, the music used is not limited to these divisions. All female and all male groups frequently sing this type of music. A barbershop quartet is one commonly recognized example of an all male group performing four part harmony. The parts in this type of group are known as tenor, countertenor, baritone, and bass, where the tenor voice generally carries the melody. The leader of the group often begins by sounding a pitch pipe to provide each singer with his beginning note. The vocalists can then perform the music a cappella, without the accompaniment of instrumentation.
This type of music may also be played by instruments alone. When four part harmony is divided into a group of musicians, it is often between a quartet of identical or similar instruments. For example, four violins could comprise a string quartet, or the string quartet might include a cello. Four woodwind or four brass instruments might also be grouped together similarly. This type of division of music may also be found in some orchestral arrangements, where the four parts are divided into one group of instruments for a particular portion of a larger arrangement.
Each instrument of the quartet plays different notes from the other players, and will read from a piece of music that is marked for that particular part. The first part typically plays the melody, and may be marked for First Violin, or First Chair. The players generally sit from left to right according to the part they will play. The first part is often given to the most experienced or most talented musician, and may contain more difficult rhythms than the other musical pieces.