Resources for THEORY AND PRACTICE OF PIANO TUNING
The "Cat" in the unison
Demonstration of the principle of the “cat” in unison tuning, together with isolated partials, showing its formation from phase differences in the partials.
The effect of dissipative mode-coupling in the unison can result in higher partial beat rates being similar to lower partial ones, for a given small mistuning (rather than being multiples of the lower).
In fine tuning, small tuning alterations, and/or false beating, can therefore map more significantly to relative phase changes between partials, than to changes in actual beat rate.
“Misaligned” phases in very slowly beating partials can create the effect of the “cat” in the unison.
In this demo there are three partials.
Partial 1 (repeated once):
Partial 2 (repeated once):
Partial 3 (repeated once):
The three partials together:
An actual, complex "cat" in a Steinway unison:
Headphones are necessary for all these demonstrations.
Make sure your volume is turned down before you listen to these clips, and adjust up carefully to a comfortable level.