Hi Gary, What is it that determines the degree of difficulty of a song? With recordings, now available, and with the different voices prominent, isn't this "rating" still important? Thanks, DH
"Difficulty ratings", even in carefully defined fields like piano playing, are always somewhat subjective.
Barbershop Harmony website that lists all the arrangements and their difficulties as "easy", "medium" or "hard" makes "Hello, Mary Lou" the standard as a medium difficulty. I agree.
Any director will look for things that are neither way too easy nor way to hard in all of several areas:
Barbershop voicing. (Leads have a hard time learning harmony for more than a few notes)
Range of the parts. (Highest note and lowest note of each part)
Tessitura of the parts. (Where the part mostly lies: staying low or high is harder)
Leaps in the harmony parts. (lots are hard; few are easy)
Key center shifts (are interesting, but hard. "folks dressed up like Eskimos")
Harmonic complexity. (Many accidentals make for tricky singing)
Rhythmic complexity. (counterpoint and drum-like parts are fun, but tricky)
This demands that directors have a good assessment of their group, what they can do, and how well they do it. Even one "too difficult" area can make the song never quite fly.
As a side note about considering arrangements for programming, you also consider:
General popularity of the song at its heyday (and if your target audience will know it)
Mood and style of the piece (is it fresh or repetitive in your repertoire?)