A tight blend demands an understanding and control of the four elements of sound:
pitch, timbre, duration, loudness

1) Pitch:
a) Unisons must be precise.
Exercise: have one or more vocalists hold a unison.
Then, have one singer move slowly sharp, and back in tune.
Flat, and back in tune. Notice the “beats.”

b) Chord factors need to be in tune, from the bass note up to the top notes.
Note: Piano, other instruments aren’t in perfect tune

2) Timbre:
a) Vowel Matching is crucial.
Exercise: have a group sing “oo,” “oh,” “ah” and notice the differences

3) Duration:
a) Each note should be attacked and released at the same time.
Exercise: have a few people say “Hello. How are you today?” together. Note how you can hear the slightest variation in one voice.

b) Moving sounds in the middle of notes, like dipthongs and connected or elided words, should happen together.
Exercise: Have a group say “Eight Days Sound Swell” together slowly.

4) Loudness:
a) All notes comprising a unit (background “ooh,” melodic trio, etc) should have relatively the same volume level.

b) Within that relative volume level, each part needs to be balanced based on importance:
Root of chord loudest, then fifth, then third.
Color notes (7, 9, 6, etc.) must be quieter, especially when in seconds.
Doubled chord factors should be quieter - less is needed.
Exception: Melody is always loudest.

c) Arranging note: chords tune best when spread like harmonic series.