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The cat in the unison
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These are demonstration sound samples to accompany the book Theory and practice of piano tuning (Brian Capleton PhD).
These samples are made available independently by the author as a free educational resource, and do not form part of any contract or sale.
Licensing information
These samples are licensed for single user non-commercial educational use only and may not be redistributed.
The "cat" in the unison
Commentary by Brian Capletron PhD:
Expert fine tuning of unison string groups achieves fine tone adjustments to the unison. One of these is an adjustment to a changing "vowel sound" in the tone of the unison. This is sometimes referred to as the "cat" in the unison because of its similarity to to the meowing of a cat.
The perception of "vowel sound" as a vowel sound rather than as the acoustical components causing it, is of course rooted in the psychology of aural perception. The actual acoustical components are partials whose envelopes fluctuate, the simplest fluctuation-type being the straightforward "beat" as proposed by "traditional" tuning theory.
The following is a simple and transparent example of how straightforward slow beat patterns can combine to produce the perception of a changing vowel sound - in this case a "cat". With a little practise it shouold be possible to psychologocally "flip" from hearing beating partials to hearing the "cat" vowel change, at will, or to be able to hear both, simultaneously.
Here is the first beating partial.
Here is the second beating partial.
Here is the third beating partial.
When all three are heard together, the changing vowel sound or "cat" is produced.
For more sharpening of the aural perception listen to the following unison, in which both changing vowel sounds and fluctuating partials can be heard. Note the initial prominent beat in the third partial, and the final prominence of the second partial, which decays much more slowly than the others.
