It has already been said that to tune a clean unison, it is important that you
focus on tuning the higher partials clean because for any given out-of-tune
unison, the higher partials beat faster, so it is easier to hear if a unison is not
clean by listening to those higher partials
Partials 2, 4 and 8 are just octaves above the fundamental, so they may be harder
to discern. Partials 3 and 5 are different notes so they seem to stand out more.
Partial 5 being a M3 (instead of the more similar partial 3 - the P5) it
can be easier to pick out and has the added benefit of being more "different"
than partial 5 and certainly more unique sounding than partials 2, 4, and 8.
For that reason, this exercise has each unison filtered a bit at the 5th partial.
Tune the unison clean, listening at the 5th partial - the M3 - and tune it until it is still.
Click the [Play Bichord] below.
It is not in tune. Tune it beatless listening at the partially filtered 5th partial.
NOTE: When you click the [5th Partial] button, you will not hear the beating
of the 5th partial. You will only hear the pitch of the 5th partial.
It's when you click the [Play Bichord] button that you will hear beating,
IF the unison is not tuned right.